CHAPTER V._Photo-Lithography

THE HALF-TONE PROCESS FOR PHOTO-LITHOGRAPHY.

The half-tone process is used in photo-lithography to reproduce

originals which do not contain distinct lines or points, but closed

tones, which are executed either in one or several colours. With this

process any coloured picture, oil, water, pastel, indian-ink or sepia

drawing, as well as any photographs from nature of living, moving

scenes, or still life objects can be prepared for reproduction on the

printing press.

I will first describe briefly the theory of the process, and then come

to the practical part.

As regards the photographic part and the quality of the negatives, in

the present state of this method of reproduction the same principles

apply as in line reproduction; where they differ I will mention the

same.

The duration of printing, the transfer of the image to the stone, as

well as the other arrangements will be described in the different

processes.

We divide this chapter again into two sections:

1. Methods in which the half-tone is broken up when making the negative.

2. Those methods in which the formation of the grain is effected after

the negative has been made by some suitable means.

1. BREAKING UP THE HALF-TONE ON THE NEGATIVE (AUTOTYPY).

Of the various methods by which a breaking-up of the half-tones can be

obtained, the so-called “autotypy” is the one most used practically.

With this process the half-tones are broken up in the negative.

As every important technical discovery is formed not at once, but

must be made by a longer or shorter series of smaller discoveries or

improvements in order to attain the hoped-for goal, so was it also with

autotypy.

From the work of Paul Pretsch, Mariot, Brown, and Fred. E. Ives the

present state of the certain and beautifully-working half-tone process

gradually evolved, and the last process, which ought to be considered

as the immediate predecessor, is far outshone by autotypy as now

practised.

Early attempts were made to obtain a printable image on stone by

breaking up the chromated gelatine film, so that an irregular so-called

serpentine grain was formed on it, which corresponded {68} fairly

well with the theory of lithography, but gave no precise lines and no

beautiful gradations of stone. If the grain was somewhat too coarse the

effect of the picture was lost, the tone gradations were too far apart,

and only light and shadows were given; if the grain was too fine the

stone was not printable.

A further experiment was printing a design over the original, the

strength of which had to be brought in correct proportion to the

original; the impressing of a design was also tried, and when using

this method the correct angle of the incident light when making the

exposure had to be taken into account.

Further experiments, which were principally carried out by Mariot,

Cronenberg, and others, were founded principally on the basis of

breaking up the tones in printing. For this a lineature or screen on

glass, or a gelatine film, was introduced between the negative and the

sensitive film. Others, again, coated the blank glass plate with a

lineature, and prepared the plate afterwards with collodion or gelatine

emulsion for the exposure.

It will be thus seen how this method of reproduction developed step

by step till net-work of silk muslin or woven horsehair, and finally

grating images, strongly reduced by photography, were placed in front

of the photographic plate.

Thus were efforts made to make half-tone pictures suitable for printing

by litho- or typography, and although the end was very nearly attained,

yet the crux was not quite solved. These methods did not, however,

yield the desired result, namely, a beautiful sharp clear image. There

was still required a considerable improvement of the existing methods,

and this was made by Meisenbach, of Munich.

The principle by which Meisenbach prepared his images was essentially

different from the previously-described results. He broke up the

half-tones, also by means of a lineature, into a printable grain,

but the process was essentially different from the previous methods,

in that Meisenbach used a glass plate on which, on a black ground,

a grating was drawn till the glass was laid bare, and in this way

prepared a lineature which consisted of clear glass, transparent lines

and absolutely opaque lines.

He produced, first, an ordinary negative, from this a positive, and

from this, by the interposition of the lineature, the actual half-tone

negative for making the printing plate. The lineature or screen was in

the second exposure interposed before the sensitive plate, and half the

time of exposure given; then the screen was turned till the line first

obtained crossed the second at an angle of 90°, and then the exposure

was completed. By this means an absolutely certain breaking up of the

half-tones into mathematically exact points was attained, and the most

important step made in making photography useful for preparing printing

plates for the two principal methods, typographic and lithographic.

Meisenbach has called his process “autotypy.” It was, indeed, {69}

somewhat inconvenient, but had the advantage that on the negative and

also on the positive any retouching that was necessary could be done.

I cannot here enter into the numerous simplifications and improvements

of Meisenbach’s process which, as well in the photographic process as

also in the preparation of the lineature, were in the course of time

made partly by him and partly by Carl Angerer, Gillot, Bussod and

Valadon, Lefmann, and others, since, on the one hand, it would carry us

too far, and, on the other hand, they may be considered as a natural

consequence of the discovery. I will only mention that it was found

after a short time that the two exposures and the production of the

necessary positive could be omitted, and that the lineature could be

simply interposed before the sensitive plate in the first exposure, by

which an important simplification of the work was attained, and, thanks

to the continued perfecting of the processes, no detraction of the good

results was thus produced.

I do not consider it superfluous to give a short explanation of the

action of the interposed lineature on the photographic plate during

exposure.

If we take, for the sake of simplicity, not a picture, but a scale

with four or five-tone gradations from light to deep black, the light

tones will act more or less on the sensitive photographic plate

according to their degree of brightness, but as the rays of light have

to pass through the cross-lined screen interposed between the lens and

sensitive plate, and as the rays can only pass through the transparent

parts and not through the opaque, no homogeneous surface is obtained

on the negative, but a tone produced by the cross-lines of the screen.

If the tone was very bright, the rays reflected with great intensity

on the sensitive plate will completely decompose the silver film.

Since they are prevented by the screen from acting with equal power on

all places of the surface, these places will show very plainly on the

negative, and the result is therefore a darker tone on the same, which

is marked with bright fine lines, corresponding in thickness to the

screen plate.

If the original tone was darker so many rays of light will not be

reflected, and these have thus not the power to impress the screen on

the sensitive plate in full intensity; the result is therefore on the

negative a tone which does not contain such strong dark lines as the

first; the tone appears lighter in the negative, and in the print from

the same darker than the first.

In the reproduction of deep black surfaces finally no rays of light are

reflected, therefore no rays of light can penetrate through the screen,

and because actually here no chemical change of the light sensitive

film takes place, we obtain a negative which is clear and transparent

in these places, that is to say without any interruption, which gives

in the print a full black tone. {70}

In this process there comes, however, to our aid a very important

physical law, namely, the diffraction of light. A ray of light passing

through a round hole or a slit and falling on to a black surface is

represented not the same size as the slit, but more or less broadened

the more the receiving surface is moved away, and in the middle the

brightest light will be, and this gradually fades off into shadow

towards the margin.

If we take now the opposite, and use instead of the hole or slit a

black surface or a conglomerate of such in the form of points, squares,

or other geometrical figures, and if these be placed before a screen

illuminated with a bright light, these figures become somewhat smaller

with this bright illumination, whilst with a weaker illumination they

are represented in correct strength.

Where the light acts in its full intensity, or in excess, in a

manner of speaking it is diffracted or bent over the figures, and

proportionately makes them smaller.

This law does good service in autotypic work.

As we have seen, the rays of light must pass through the screen during

exposure. This screen consists of equally thick opaque black and

transparent white lines. Where the light acts with full intensity it

will be more diffracted over the black lines. It makes the lines of the

screen broader on the negative, and will, therefore, have more covered

places, which in the after printing of the prints cannot be penetrated

by the light, and thus represent the light places in the print covered

with fine dots.

The darker the tone the less the rays of light reflected, and the

less, therefore, can the light be diffracted. As the tones get darker

the lines of the screen become of equal value on the negative, till

finally, when at the opposite end of the screen, they totally disappear

in the deep blacks.

A valuable quality of a correctly-prepared autotype is, therefore, that

the covered lines or the covered grain appear of different strengths on

the negative. In the high lights they are stronger, in the half-tones

weaker, till finally in the black parts they have totally disappeared.

A further not less valuable property is that the grain in the highest

lights is not sharply defined, does not appear as a square point, but

is rounded by the diffraction of light, which gives a softer, more

beautiful appearance and plasticity.

Whilst the light reflected from the brightest parts of the drawing acts

with full intensity, and is diffracted over the figures standing in its

path and makes the same smaller, and cuts off the sharp corners and

gives more covered surfaces to the negative, as it decreases according

to the more or less deep shadows of the drawing, and can only act now

with less intensity through the open places of the screen, the result

is that the points become larger, till finally in the deepest parts it

is quite inactive, and the shadows begin to block. The action of the

light rays of different {71} strengths reflected on to the negative

in accordance with the brighter and darker tones of the drawing,

taking into consideration the print, can be graphically represented

as a pyramid of which the base represents the deepest shadows and the

point the high lights. If we interpose a cross-lined screen, or more

correctly called a grain plate, before the sensitive plate, we obtain,

graphically considered, grain figures, actually of many more very

different sizes, as shown in Fig. 7, 1–6, in which the smallest points

represent the high lights of the drawing, and those becoming gradually

bigger the gradually increasing shadows.

[Illustration: Fig. 7.]

The original grain plate contained, measured diagonally, five black

points, five white interstices to the millimetre. The figures represent

enlargements of a negative made with the above-named grain plate, and

for this the grain plate was one millimetre distant from the sensitive

plate.

The accompanying Figure 8, 1–6, represents very much enlarged the

scheme of grain of an autotype from a perfectly-executed wash drawing,

with a screen of five opaque and five transparent lines to the

millimetre, in equal proportions of black and white, at a distance of

one millimetre from the sensitive plate, with equal time of exposure

before and after the turning of the screen, and obviously with correct

exposure for the whole.

The scheme is only given here in six gradations of tone. As a matter of

fact, a good autotype has at least from six to eight times the number

of tones, as with a sharp screen and an original cleanly {72} and

sharply drawn in many tones, the light reflects the least alteration of

tone in the size of the grain.

[Illustration: Fig. 8.]

As previously mentioned, the smallest points represent the highest

lights of the drawing; the larger, according to our graphic

representation, the darker tones, but a correct reproduction of the

grain.

In a similar way obviously the formation of the lines on the negative

behave with an interposed but not revolved screen. Here also the lines

in the high lights of the negative appear more covered than in the

shadows.

The proportion of grain can, if the original requires it, be so

far altered by not giving equal exposures for each position of the

screen—for instance, in the proportion of two to one or three to one.

We obtain then on the given scheme less closed tone gradations, 3, 4,

and 5, and just before 3, and between and after 5, tone gradations, no

single black and white points, but more or less jagged black or white

lines, whilst the open black grain in 1 and 2 becomes more an oval

instead of the round form in 6, and beyond the round openings are drawn

out into ovals.

We have, however, in autotypy still the physical law, which is very

useful to us, and that is the greater or less distance of the point

from the light surface. The nearer a point or a figure is brought to

the wall on which it should throw the shadow, the greater the size

of the original, and so much sharper will be the outlines of the

shadows. The more the point or the figure is {73} removed from the

wall the less the shadow will correspond to the shape of the original;

it will be smaller and less defined. The shape will also frequently

change, and a square will become a round. We have then in the near or

distant position of the lineature to the sensitive plate, on which

it throws its shadow, an important assistance to act on the general

tone gradations of the image. Let us remember that in focussing the

shadow-forming object on to the surface on which the light falls, we

obtain the same formed in all its actuality on the receiving surface;

therefore, when this refers to a lineature with equal proportions of

black and white, we obtain these in equal ratio. When, however, we

remove the lineature from the light-receiving surface, the shadows

which it throws contract, the lights predominate, we obtain no longer

the ratio of 1 : 1 between light and shadow, but about 1·5 : 1 and so

on.

By placing the lineature close to the sensitive plate, we obtain more

closed tones, and as this gradation of tone is carried naturally

throughout the whole of the image, also less high lights, less deep,

middle shadows, whilst the deep shadows appear in their natural

strength. With the removal of the lineature from the sensitive plate,

on the other hand, the ratio of tones for the whole image, as well as

for the details, is displaced. In the first place we shall obtain a

picture which contains more contrasts of black and white. The light

tones become considerably lighter by the reduction of the shadows. The

dark parts, on the other hand, attain full vigour. In the first place,

therefore, the original has to be considered as regards the distance

of the lineature from the sensitive plate. Obviously, therefore, no

accurate directions can be given in a case where feeling and experience

are required. Next to the original, the number of the lines on the

screen has to be considered. As a rule, one uses lineatures with five

or six transparent and opaque lines to the millimetre (= 125–150 to the

inch), and for these a distance of ½ to 1 mm. (= 1⁠/⁠50–1⁠/⁠25th inch)

from the sensitive plate is generally sufficient for most cases. With a

less number of lines the distance can be increased.

Autotypy is a process in which unprintable half-tones can be broken

up by the use of a well-defined physical law into a mathematically

determined grain, and the size of the grain can also be regulated to a

certain extent with certain precautions.

It is, therefore, easily understood that the autotypic process is now

very general and most used, and not only in the limited department of

photo-lithography, but in a more extended way, does excellent service

for the preparation of illustrations of all kinds, for the simplest

picture for the daily paper as for the finely-printed magazines and

journals, for simple monochromatic printing, and for the highest colour

printing.

With accurate knowledge and command of the technique of {74}

photography and lithography, there is required before everything,

for successful work, a faultless screen plate. The indispensable

requirements which must be found in the screen are absolutely opaque

black lines and bare glass in the white lines. The home preparation

of such a screen plate is a somewhat difficult matter, and will not

be absolutely successful if one has not a faultless ruling machine, a

composition which is thoroughly opaque, which adheres well to the glass

and gives clean, sharp lines in ruling, and which does not chip, and

it will require a tremendous expenditure of patience and perseverance.

Glass screens of excellent quality may now be obtained commercially.

For reproduction of the very highest quality, a drawn and etched screen

plate is more suitable than one merely ruled on pigment, which never

gives such sharp results.

From various firms etched screen plates may now be obtained either as

single or crossed-line screens, which fulfil all requirements.

The best screen to use is one with five or six opaque and transparent

lines to the millimetre, which corresponds with 2,500 to 3,600 points

to the square centimetre. The above number of lines will suffice for

nearly all work, and such screens give reproductions in which the grain

is no longer visible to the naked eye, but appears as a closed tone. It

is not advisable to go beyond this number of lines, except in special

cases, when the details of the drawing in the original are specially

small. With a smaller number of about three or four lines to the

millimetre, too coarse a grain results, of which the individual points

become too plainly visible, and these are distracting and act roughly,

and do not accurately reproduce the gradation of tone.

The best proportion between opacity and transparency is 1 : 1. From

this is obtained, according to my opinion, the most beautiful and

restful tones. It must also be remembered that the opaque spots

actually lose considerably in strength in the brighter portions of the

picture by the spreading action of the light.

The printing may be done on bichromated gelatine paper, with which,

however, extremely accurate inking up of the print is essential, and

the prints must not have too much ink and must be very carefully

printed. If, however, very good, clear negatives are used, either of

the direct printing methods, as already described in Chapter IV., is to

be preferred. (See No. 4 Supplement.)

2. PHOTO-LITHOGRAPHIC PROCESSES IN WHICH THE GRAIN IS NOT FORMED DURING

THE EXPOSURE.

Of the many existing processes by which the breaking-up of the

half-tones into printable lines or grain is effected, not in the

negative, but subsequently by mechanical and chemical action on the

stone or plate or the transfer film, I will only mention those {75}

which appear to me to be the most important, the new methods which

have already found firm footing in practical work or which appear

likely to do so. All the older processes, which were either never

actually successful or have been superseded on account of difficulty of

working, we may properly pass over.

(A.) THE PATENT ASPHALT PROCESS OF ORELL, FÜSSLI, AND CO. USED FOR THE

PREPARATION OF COLOUR PRINTS.

I have already mentioned that the use of light sensitive asphalt for

the preparation of printing plates for the various branches is by no

means new.

The fundamental principles of the well-known processes we find also

used in the process of Orell, Füssli, and Co.

The grained stone is coated with a thin film of light-sensitive

asphalt, the composition of which we have previously learnt, and

exposed under a reversed or stripped negative. The image after correct

exposure is developed, and then, according to the construction of

the asphalt, in combination with the graining of the stone and the

developer, there is formed a finer or coarser grain, or a closed or

open image.

The development is effected with petroleum, to which one-fifth or

one-sixth of its volume of benzine is added, or with turpentine alone.

Development takes place rather rapidly, and after a short time the

image appears on the stone. The print is then treated as was suggested

in asphalt printing; the stone is first gummed, and then by rolling

up with ink and etching rendered suitable for printing. The pictures

produced by this have a very fine grain and are in appearance very much

like good collotypes; still two or more tones are necessary to obtain

an absolutely closed and vigorous action.

Very similar to Orel and Füssli’s process is the following, also

patented.

(B.) THE COLOUR PRINTING PROCESS OF WEZEL AND NAUMANN OF REUDNITZ,

LEIPZIG.

In this process also all the colour stones of a chromo picture are

produced from a single stripped and reversed negative which is taken

of the original. For the preparation of any colour stone there are

three distinct stages. The first stage is the exposure, the second the

development, and the third the development continued still further,

and any necessary small help by the lithographer. In each stage a

special mode of treatment is required, according to whether the stone

in question is to be used for a light, a more vigorous, or full colour.

The stones for grey and the light blue or light red inks—thus those for

many surfaces, but with few details—are treated differently to those

for yellow, the second red {76} or blue; and these, again, differently

to those for brown or quite dark colours.

Everyone only slightly conversant with colour printing knows that

the first plates are used for the general tones of the picture, and

contain, therefore, few details, and with the exception of the highest

lights are tolerably full; the latter plates, on the other hand, which

are devoted to the darker colours, contain less toned surfaces, but,

on the contrary, more details of the drawings. In order to attain this

correctly the three stages of the production of the plates are carried

out with this end in view.

It should still be mentioned that the more or less fine graining of the

stone determines the general ratio of the grain of the picture.

The first stage is the exposure of grained stone coated with asphalt.

With longer or shorter exposure it is possible to make the asphalt film

more or less soluble, that is to say, to make the same more or less

capable of resisting ethereal oils.

It is therefore possible at this stage, by long exposure of the asphalt

film, to give to the colour stone for bright colours more tone and less

details. The stones for the darker inks are printed for a shorter time,

and the asphalt film is less capable of withstanding the solvents, and

the resulting plate contains less tones and more details. Finally, the

plates for the deep colours are normally printed; the asphalt film is

still less resistant, and consequently the stone will only have tone

and details on those places which in printing ought to be the darkest.

It is possible, therefore, by correct manipulation of this operation,

to obtain approximately the correct colour plate.

There is, however, in the second process a corrector for the first. The

development may be so performed that by the longer or shorter use of

strong solvents, Hungarian or Russian turpentine, more or less of the

asphalt will be dissolved. Thus if a slight error is made in printing

it can be made good in developing. As a rule, the stones for bright

colours, which consist of many tones, are not developed so long as

those for the stronger colours. The actual stones for the deep colours

are very strongly developed, so that almost all the delicate parts of

the picture disappear, and only the dense strong parts remain on the

stone.

Still the fine details which are to be found in the vigorous parts, and

which cannot be recognized, must be brought out. The fine parts of the

drawing must be quite clear if the details are to be recognized, or the

picture will be a fuzzy copy of the original, wanting in structure.

This fault is remedied in the third stage of the treatment, in which a

strong development of the picture is effected with strong acting oils

or benzole and turpentine. As this operation, however, would also wash

away such delicate places which ought to remain on the colour stone,

they must be covered with solution of gum and allowed to dry. Then

those parts not covered with gum, {77} in which the details of the

image cannot be seen, are painted for a longer or shorter time, as may

be required, with a brush dipped in the developing solution, and when

correctly developed may be covered up. The lighter places are treated

for a shorter time, the very dark places for a longer time.

By this treatment the particular parts of the picture become lighter

and lighter, the details appear more and more; and, finally, the whole

picture shows as it should do. Then the gum is washed off and the

stone subjected to the already described treatment, so as to make it

suitable for printing in quantities. Finally, the lithographer can make

corrections with a needle or tusch.

This process may be used, therefore, to prepare colour-printing plates

from a negative obtained in the camera from an oil painting or any

coloured original.

The negative for this process must contain all the details very clear,

must be soft, and not be too dense.

The different colour plates are thus in this process obtained by long

or short printing, by strong or weak developing, and finally the

details in the dark plates are obtained by separate development and

covering up the other places with gum.

The breaking up of the half-tones into printable grain is effected by

graining the stone, before coating with the light sensitive asphalt

film. On the finer or coarser graining of the stone depends also the

structure of the grain of the image.

This process yields the most beautiful results with correct

manipulation, and in the hands of an expert photographer and

lithographer is a valuable aid to the preparation of colour plates. The

process is patented.

(C.) J. BARTÖS’ PROCESS FOR PREPARING PHOTO-LITHOGRAPHS AND PHOTOTYPES

IN GRAIN AND HALF-TONE.

Bartös’ process belongs to those in which the breaking up of the

half-tones into a printable grain is effected subsequently on the plate

or stone by mechanical means. This is attained in a very original

manner by means of a sandblast, which makes the half-tone printable.

We have here not the breaking up of the half-tones in a mathematically

regular manner, dependent on optical laws, as is the case with

autotypy, but a method similar to that of Pretsch, which obtains the

printable grain by reticulation of the chromated gelatine film, or

other discoverers who attain the same result by asphalt dusting or some

other means.

For this process a well-polished litho stone or zinc plate is coated

with a thin film of varnish, composed of—

Chloroform 300 g.

Mastic 5 g.

Asphalt 10 g.

Benzole 300 g.

Linseed oil 2 g.

{78}

On the stone or plate thus prepared is transferred a carbon image in

half-tone.

This pigment film, when completely dry, is flowed over with a mixture

of—

Glycerine 35 g.

Water 25 g.

Alum 2 g.

and this should be allowed to act for about five minutes and then

removed with blotting-paper. After this operation the pigment image can

be easily destroyed. The pigment image is now exposed to the action

of a weak sandblast. The sand acts on the relief image and gradually

destroys it, and so that the film of varnish underneath is gradually

grained.

After the pigment film has been removed the picture shows in all its

details in grain on the varnish of the stone or plate. The image is now

visible on the film of varnish, according to the strength of the tones

in partial graining, and can be etched into the stone or plate.

This is effected by etching with phosphoric acid—

Water 100 g.

Phosphoric acid 4 g.

When the etching solution has acted for about two minutes, the stone is

washed and coated with a solution of gum—

Water 100 g.

Gum arabic 5 g.

and allowed to dry.

Then the film of varnish is removed with a pad of cotton wool damped

with turpentine, the dry stone rolled up with litho ink, damped, and

the excess of ink rolled off. The picture now shows with all its finest

details on the stone, and can be printed.

In preparing a relief printing plate the film of varnish forms the

resist for the first etching. It is then rolled up and etched in the

usual way.

For preparing larger pictures on stone or metal plates, in which the

grain must be coarser than with small pictures, the fully-developed and

still damp pigment image is dusted with powdered resin and the film

allowed to dry with the powder adhering to it. The pigment image thus

dusted is treated, as previously described, with alum and glycerine,

exposed to the action of the sandblast, and then etched with phosphoric

or nitric acid.

As the soft pigment film receives a grain by the dusting, this is

reproduced of the same size by the action of the sandblast on the film

of varnish on the stone or plate.

The principal points of this process of preparing photo-lithographs or

phototypes in half-tone, with a grain, are as follows:—

1. From the photographic negative a pigment image is taken {79} and

transferred to a litho stone or zinc plate, which has been previously

coated with varnish.

2. The pigment image is then exposed to the action of the sandblast; and

3. Then the pigment image is removed, and the image obtained on the

film of varnish is etched.

In the K.K. Hof und Staatsdruckerei photo-lithographs as well as

phototypes have been prepared with excellent results by this process.

The former in result are similar to the productions of the Orell and

Füssli process, and the latter were noticeable for good gradation.

On the other hand, it cannot be denied that this process, which is

patented, has been already surpassed by autotypy, which is far simpler

and easier to work, and is founded on a scientific basis.

(D.) LITHO-HELIOGRAVURE.

This process, invented by Chas. Eckstein, of Hague, the general

director of the Topographical Bureau of the Royal Netherland General

Staff, also belongs to those processes of photo-lithography by means

of which any picture in half-tone can be reproduced. The breaking up

of the half-tones is effected, as with the autotypic methods, by the

use of a lineature, but instead of this being done in the photographic

exposure, it is effected direct on the stone before the transfer of

the photographic image. In this particular process the stone itself

is not coated with a light sensitive film and printed on direct, but

the ruling is made on the stone, and then a negative pigment image—a

diapositive—is transferred to it exactly the same as with photogravure

on copper. A further feature is that the result is not an ordinary

transfer stone result, but an intaglio etched stone, which is printed

from the depressions.

For this original process the basis is a ruled pattern stone, prepared

with great care and accuracy. For preparing this a grey stone of

the best quality should be taken, and one without any chalky spots,

crystals, or holes. This should be polished with a coarse cloth

and oxalic acid solution till it has a very high polish. On the

highly-polished stone surface is spread a very thin but even film of

asphalt.

The solution is composed of—

Asphalt 5 parts.

White wax 6 parts.

Stearic acid 6 parts.

This mixture is boiled, and to it whilst boiling is added in drops a

solution of two parts of soda. When cold this mixture, which is fairly

hard, is dissolved in about an equal volume of turpentine, filtered and

kept in bottles for use.

A sufficient quantity of this asphalt solution, which must not be

sensitive to light, is poured into the middle of a levelled stone and

{80} distributed by means of a lithographic ink roller, which must not

be used for any other purpose but this, till the coating is absolutely

even and shows a light brown colour.

When this film has become quite hard, fine parallel lines are drawn

over the whole surface of the stone with a very accurate working ruling

machine, by means of which from five to ten lines per millimetre can be

ruled.

When the ruling is finished the stone is given a margin of wax, and

quickly and evenly flooded with the following etching fluid—

Pure nitric acid 0·16 parts.

Alcohol 36 per cent. 0·60 parts.

Water 35 parts.

And, watch in hand, is etched for about half-a-minute.

Instead of the above a solution of—

Glacial acetic acid 2 g.

Water 100 g.

may be used and allowed to act for half-a-minute. The stone is then

well washed under a strong stream of water, allowed to dry, and covered

with linseed oil. After about five minutes the whole of the stone may

be washed with turpentine. Then it should be inked up with a pad, care

being taken that all lines take the ink well and evenly. This pattern

stone serves as the original plate for the subsequent ruled transfer.

From the original ruled stone can be made, according to the nature of

the original, a single, double, triple, or four-fold transfer.

For preparing a stone with a ruled transfer, a smoothly ground stone

well polished with oxalic acid is evenly coated with sensitive asphalt

solution. On this, when dry, the desired single or crossed transfer

from the original stone is made, and dusted with bronze powder. This

adheres to the lines of the pattern, and in combination with the

printing ink protects the asphalt film underneath from the action

of light. During the subsequent exposure, which, according to the

sensitiveness of the asphalt and intensity of the light, can last from

a half to two hours or more, the particles of asphalt not covered by

the bronze powder become insoluble, whilst the protected parts preserve

their solubility.

After correct exposure the surface of the stone is carefully washed

with a tuft of cotton wool soaked in oil of turpentine, when the

particles of asphalt underlying the bronzed lines dissolve. The stone

at these parts is laid quite bare, and therefore made capable of being

subsequently etched. The deep etching of the pattern is effected in

the same way as was suggested in the preparation of the mother pattern

stone.

By this method a positive pattern is obtained, that is to say, the

lines print, and the impression shows therefore a black network.

A second method of making a pattern transfer consists in making a

pull from the original stone on to chalk transfer paper. {81} This

pull is then damped on the back, and when just properly damp is laid

on the polished stone (without any asphalt) and the transfer made.

In order to remove the chalk paper without damaging the pattern the

stone is covered with warm water, when the lines will dissolve. The

simple pattern will now be found on the stone, which should now be well

washed, then dusted with resin powder, which should be melted on with

ether vapour. Then if the direction of the first lines was vertical,

the second transfer is arranged with the direction of the lines

horizontal to the first, and there is thus obtained a simple crossed

pattern. With four-fold crossed patterns the subsequent pulls are made

in opposite diagonal directions. After each transfer the stone is well

washed, allowed to dry, then dusted with resin powder, and with ether

melted on to the pattern.

The stone is now deep etched with dilute nitric or acetic acid and

covered with linseed oil.

By this method a grain instead of lines is obtained. By polishing the

stone and transferring on to it, as well as by etching the places not

covered by the ink, we have the pattern reversed, that is to say, it is

converted into grain.

For further operations of litho-heliogravure a very clear and soft

negative is required, from which a glass transparency is taken. Under

this transparency pigment paper sensitized on a 20 per cent. solution

of potassium bichromate is printed to 8 or 10 degrees Vogel. Printing

must be very carefully performed, as with under-printing too many

details are lost. The exposed pigmented paper is washed in cold water,

laid film side down on the previously prepared stone, and pressed into

contact with an india-rubber squeegee. It should then be allowed to dry

in a not too dry or too warm place.

The stone should now be placed in a trough with warm water of about

40 to 45° C., and care should be taken to obtain water of as even a

temperature as possible. After about five minutes the paper will be

free from the stone, which should remain in the bath and be developed

so long by shaking in order that the water may flow evenly over it till

the image appears quite distinct; a negative image is thus obtained on

the stone. The film is then allowed to dry spontaneously for four or

five hours till the pigment image has become quite hard.

For etching a solution of perchloride of iron of various strengths is

used, 40, 37, 33, and 30° Beaumé. With subjects very rich in tones

all four will be used; with simpler subjects one or the other may be

omitted.

The etching will begin, as a rule, with the 40° solution. The ferric

chloride will first dissolve the thin, hardened pigment film and then

go through the open lines of the pattern, where it will attack the

stone and etch the deepest parts.

Slowly the ferric chloride dissolves also the thicker pigment {82}

film—begins also to etch the stone there, but less deeply. To tell

when the four solutions should be used in turn, as well as the correct

moment to interrupt the etching, requires considerable experience. The

30° solution, the weakest of the ferric chloride solutions, is used

last, and in consequence of the greater proportion of water possesses

a solvent power for the whole of the light-hardened pigment film.

Accurate directions as to how long the etching with the different

solutions is to be continued cannot be given, as this depends upon the

character of the subject as well as upon the thickness of the pigment

image. It may be always assumed, however, that any individual etching

ought to last under no circumstances longer than three to four minutes.

With well-covered stones the first etching should not be allowed to act

so long as the last, and _vice-versâ_ with less covered stones.

As soon as the image shows the correct character through the etching

solution the stone should be brought under the tap in the trough and

quickly washed with clean cold water. The surface of the image should

then be flowed over with oil of turpentine in order to remove the

asphalt and gelatine film, and finally well washed with the rose and

allowed to dry. The picture will be found deeply etched into the stone.

The stone is now smeared over with linseed oil, inked up, and further

treated as in ordinary lithogravure.

In this process the negative pigment image is transferred to the stone

and the printing image prepared by etching; the formation of the grain

is produced by the pattern printed either on a polished stone, when

it is converted into points, or the transfer may be effected on to an

asphalted polished stone, when a network of lines will be obtained.

For dark subjects the latter process is better, for lighter subjects

the grain.

Printing from such a plate has more similarities with etching printing

than from stone; the effect of the ink is very good and expressive.

Various pictures executed by Eckstein and in our establishment in one

or more colours have proved the value of this process in practice.

The foregoing are the different photo-lithographic methods for

obtaining printing images in half-tone, and although in no way

exhaustive, yet it appears to me that they are practically the most

important.

{83}

APPENDIX.

1. NEGATIVE TRANSFER WITH BICHROMATED GELATINE PAPER.

The properties of bichromated gelatine paper can also be very well

used for the so-called negative printing, and this method offers many

advantages.

In order to convert a positive printing image into a negative various

methods may be used; the most convenient for the lithographer is the

following:—A good litho stone is first ground in the ordinary way and

then the surface rubbed with a pad and oxalic acid solution till it

has a high glaze or polish. On to this stone is then transferred a

sharp impression in a non-greasy ink from the positive printing image.

According to the destination of the stone for large or small editions

one of two processes may be adopted. If a thousand or more pulls are

required from the stone the transfer may be dusted with resin powder,

and this melted with the burning, heating, or ether process and the

drawing etched in relief with 8 to 12° nitric acid and gum. Then the

stone may be well washed with water and the acid removed with one to

two per cent. acetic acid.

For small runs the first etching is omitted, and the stone treated with

acetic acid. In both cases the stone should be well washed, dried, and

then coated with dissolved lithographic tusch or autographic ink. The

greasy substances of these materials penetrate into the surfaces of the

stone that are laid bare, and firmly adhere. When the tusch or ink is

completely dry the stone is washed with turpentine, inked up, and one

now has a negative image from the subject in question, which shows all

the original printing places in white and all white places black.

The process of preparing such negative prints by the use of bichromated

gelatine papers is much simpler.

A sheet of gelatinized paper is sensitized for this purpose on a 5 per

cent. bath of potassium bichromate, squeegeed to a sheet of plate-glass

and well dried, and on this is made with black ink, which is very

opaque, in the dark or in gaslight, a sharp clean print. This print

is then laid on a flat cable, under a sheet of plate-glass, so that

it cannot roll up, and exposed to the light for from five to thirty

minutes. A long exposure rarely does harm in such cases, as the good

opaque black ink allows no rays of light to pass through to those

places which later should print white.

The next manipulation is the development and inking up, which is

done as in ordinary photo-lithography. In this operation all {84}

those places which were not covered up by the printing will take the

developing ink; on the other hand, those places where the impression

was will wash out clean and white. The print has assumed the appearance

of a photographic positive. The print is now treated like any other

photo-lithographic print, and finally transferred to a stone or zinc

plate. This method is distinguished by its simplicity and safety;

it has also the advantage that any desired printing subject can be

directly transferred in negative form to a zinc plate for relief

etching, which otherwise could only be done by preliminary transfer to

stone and subsequent transfer to zinc.

2. PHOTO-AUTOGRAPHY.

DRAWING WITH AUTOGRAPHIC INK OR LITHOGRAPHIC CHALK ON A CYANOTYPE,

SALTED OR OTHER PRINT FROM A PHOTOGRAPHIC NEGATIVE OR POSITIVE.

By autography we understand that method of reproduction by which any

writing or drawing is made on a prepared or not prepared paper with

greasy ink, tusch or chalk, which is subsequently transferred to stone

or zinc for printing, or to zinc plates for relief etching.

Autographic drawing papers differ for the different purposes, and for

writing and simple line drawings smooth hard post paper is used, and

lined transfer paper for fine pen or chalk drawings. The latter are

prepared commercially by Angerer and Göschl. Very beautiful grained

drawings can also be made for transfer on pyramidal grain paper. The

proof for such drawings is usually done with lead pencil or red chalk,

or it may also be made on a gelatine proof.

In order to obtain fully and completely the character and correct

reproduction of the drawing, without special expense of artistic help,

it is advisable to use a photographic print as proof. It should be

noted that for pen drawing on smooth paper with greasy tusch or ink,

for chalk drawings on a prepared grained paper done as previously

mentioned, with greasy lithographic chalk, the drawing should be

transferred direct to zinc or stone in order to save having to make

subsequently a photographic print.

If a pencil, red crayon, or other proof is used for an autographic

drawing on paper with the idea of transferring it direct to stone or

zinc, a suitable photographic print may also be used on suitable paper

without any disadvantages.

For the prints all photographic papers without glaze, such as ordinary

plain salted paper, Eastman’s positive bromide paper, and others, may

generally be used. Glossy or albumenized papers are not suitable for

this, as the ink runs, and does not form solid clean lines. {85}

The best of all, however, is cyanotype paper, as even with very deep

printing it keeps the details in the shadows open, and on account of

its blue tones is more suitable for the subsequent drawing with black

tusch. When, however, prussiate paper is not handy, and subjects with

fewer shadows and less details are to be treated, any of the other

papers above-mentioned may be used.

If ferro-prussiate paper is to be used, the same may be prepared as

recommended on p. 23.

The so-called salted or plain paper is prepared as follows:—A sheet of

well-sized post paper is first bathed in a solution of—

Ordinary salt 1 part

Water 25 parts

and then sensitized in a solution of silver nitrate 1 : 12. It is

printed till the print has assumed a fairly full brown tone, and all

the details in the shadows are well printed out. It should then be

toned in the following toning bath:—

Distilled water 1000 g.

Sodium acetate (twice fused) 15 g.

Solution of gold chloride (1 : 100) 25 g.

till the print has assumed a deep dark brown tone. It should then

be fixed in a solution of sodium hyposulphite, 1 : 15. It should be

printed rather deep, as in toning and fixing the image loses in depth.

It is moreover unnecessary in this case to make a beautiful print; the

chief thing is only that all details of the image should be clearly

seen. The print is then well washed in frequent changes of water and

then dried.

The print on Eastman’s bromide paper is prepared as follows:—

Red light must be used. It should be printed by an ordinary gas flame

at a distance of about 50–80 cm. (= 24 to 36 ins.) for 1 to 20 seconds,

according to the density of the negative. Here again a technically

perfect print need not be arrived at, but one which contains all the

details very clear. Under a good transparent negative a useful image

for the artist will be obtained with about two seconds’ exposure.

The developer is composed of two solutions:—

(A.) Water 500 g.

Neutral oxalate of potash 165 g.

(B.) Water 50 cm.

Sulphate of iron 15 cm.

Concentrated sulphuric acid 2 drops

Or glacial acetic acid 5 drops

Three parts of solution A and one part of solution B should be {86}

mixed together. As soon as the shadows have attained the desired tone,

the prints should be placed in several fresh baths of

Water 200 ccm.

Acetic acid 1 drachm.

Sat. sol. alum 50 g.

and then washed and fixed in a bath of

Water 50 ccm.

Sodium hyposulphite 10 g.

for about ten minutes. Then well washed and dried.

For pen drawings all not gelatinized or albumenized printing papers

may be used as already mentioned. The chief thing is that the paper

should be well-sized and of good firm texture. If prepared grain paper

is used, which is provided with a film of chalk, kaolin, or any other

white colouring matter combined with gelatine, and on which film the

grain is impressed, only prussiate prints can be used. The paper is

sensitized as previously described, only it is advisable not to leave

it too long in the solutions, or else the film may become softened. The

film will also dissolve in hot water at about 80° C.

The prints as soon as dry can be used for drawing on. On the grain

papers the outline may be drawn with the pen and be shaded with chalk,

or it may be drawn with chalk only. With unprepared papers it is

advisable to coat them with a thin solution of boiled starch, as then

the transfer to zinc or stone is most exact. The drawing may also be

left a long time without spoiling. The coating is performed with a pad

dipped into the liquid, which consists of one part of fine bookbinder’s

starch and four or five parts of water, and passed several times over

the print.

The drawings ought only to be done with greasy lithographic tusch

or chalk or autographic ink, which consists principally of greasy

materials and lampblack. For pen drawings hard pens should be used, and

care must be taken to make thick strokes. Only a little tusch or ink

ought to be taken into the pen, so that it does not run out, and thus

clean, sharp lines be obtained. If this be observed very close shadings

and cross lines can be produced clean and neat.

When the drawing is finished and the tusch or ink has become dry the

same should be laid between damp blotting-paper, and meanwhile a clean

ground, and dry pumiced stone worked in the press and the pressure

correctly adjusted. As soon as the drawing has become moderately damp

right through, and the paper feels soft without being wet, it should

be laid with the image downwards on the stone and transferred to the

same with strong pressure. After repeated working the paper will

adhere firmly to the stone. In order to loosen it the stone should be

covered with hot water of about 80° C., when the film will dissolve and

the paper become quite free. Any exertion of force must in this {87}

operation be quite avoided, and the paper must not be pulled off with

violence. All, even the finest lines, will have been transferred to the

stone. The stone is now gummed, if possible allowed to stand for some

hours, and then etched with a gum etching solution of two degrees’ acid

strength, or later etched in relief, and is ready for printing. If the

transfer is made to zinc, for printing from this the plate is treated

as suggested on p. 6. If, however, a relief etching for the typographic

press is to be prepared of the subject, the transfer is made on to a

smooth polished zinc plate.

3. LITHOGRAVURE.

With this particular process an intaglio printing stone or intaglio

printing plate is prepared by chemico-physical means.

This process was discovered and brought to great perfection by Chas.

Eckstein, the general director of the Typographical Bureau at the

Hague, and offers especially many advantages for the reproduction of

maps.

A map engraved, drawn, or transferred on stone, or written in

on copper, in originally one colour, can by this process in a

comparatively easy way be converted into a many-coloured print; this

process can also be used very advantageously for changing the names for

the places—rivers, mountains, etc. In the first place intaglio original

printing plates in all the colours can be prepared which can then be

printed for further reproduction; in the second case it is necessary to

re-engrave the network, hydrography, etc.

When it is desired to convert a monochrome image into a multi-coloured

map, as many stones as there are colours to be used must be first

ground and polished with oxalic acid till they have a high polish.

In the meantime an asphalt or other light-sensitive solution should be

prepared, with which the stone is coated in the dark very evenly, and

somewhat more than is done for a photo-lithographic print.

The asphalt solution is composed of—

Syrian asphalt 20 g.

Chloroform 300 g.

Benzole 100 g.

Oil of lavender 20 drops.

After it has been dried in the dark the impression from the black

plate, which should be previously made on transfer paper, is

transferred to the asphalt film as previously laid down, and before it

is dry dusted with bronze powder. All lines, titles, or figures which

should not appear on that particular colour-plate must be then covered

with the above asphalt solution, and only those places, for example,

on the one plate all titles, on another all the roads, on a third the

river courses, and so on, should be left, all of which later should

appear in printing. {88}

The stone is now, according to the sensitiveness of the film and the

strength of the light, exposed for from fifteen minutes to two hours.

Over-printing, if it is not very exorbitant, does not do any harm

with the stronger letters or lines on account of the good covering.

With very fine lines, however, more care must be taken. If there is

any doubt as to the length of the exposure a test may be made at one

corner of the plate with a pad dipped in rectified turpentine. When the

asphalt will no longer dissolve the exposure may be discontinued. With

some experience the photometer may also be used.

Then the whole surface should be washed with rectified turpentine and a

pad of cotton wool, when the ink lying under the bronze, that is, the

lines where the asphalt has been protected from the action of light

dissolve, and the surface of the stone appears. The rest of the asphalt

film has become insoluble from the action of light, and now forms the

etching-ground for the reversed negative image on the surface of the

stone.

When the stone has been well washed with water it may be etched, which

is done with glacial acetic acid two parts, water 100. When there are

any fine lines in the drawing the etching is interrupted at the end

of two minutes, and they should then be covered with tusch, and then

when the tusch is dry the other parts are further etched for a longer

or shorter time according to the degree of fineness. In any case the

time of etching should not exceed five minutes. The stone is allowed

to dry and then coated with a solution of tusch or linseed oil, which

penetrates into the etched parts and makes them capable of taking

ink. After about ten minutes the whole stone should be washed with

turpentine or benzole, by which the etching ground is removed, when the

stone is inked up like an ordinary gravure.

In this way is obtained a stone with deep etched drawing, which

according to the blocking contains the titles, the rivers or roadways,

and from which subsequently the necessary gravures can be taken. This

stone can either be used for direct printing or it may be used as an

original stone from which the necessary transfer can be made.

The same process may also be made for intaglio printing plates on zinc

or copper, only then the etching must be done with nitric acid or

ferric chloride.

Instead of the transfer on the light sensitive film, a drawing on

transparent paper may be used, or a photographic transparency. The

exposure in this case, as the opaque ink and bronze powder are not

used, must be very carefully estimated.

The advantage of this process is that an intaglio printing surface may

be obtained so that engraving is entirely or partially avoided, and

that this printing surface may be used as an original from which the

reproductions are made.

{89}

SCRAPER BOARDS, MANUFACTURED BY AUGERER & GÖSCHL, VIENNA.

No. 6.—A white scraper board printed with black lines. There are 40

black and 40 white lines to the centimetre; the ratio of black to white

is as 1 : 2. At right angles to the black lines impressed lines are

arranged, of which 37 are depressed and 37 raised up to the square

centimetre.

No. 7.—This is practically the same as No. 6, only that the lines are

slightly less in number, namely, 35 black and 35 white and 26 impressed

lines in equal areas to No. 6.

No. 8.—This contains dots instead of lines, both black and impressed;

there are 1,156 black dots at regular intervals, and 961 impressed dots

to the square centimetre.

No. 9 is a smooth scraper board.

Nos. 10 and 11.—These are impressed with straight lines in the

proportion of 1 : 1. With No. 10 there are 27 lines, in No. 11, 37 lines

to the centimetre.

Nos. 12 and 13.—These are impressed with lines at right angles to one

another, so that regular squares are formed. No. 11 contains 730, No.

12, 1,370 squares in every square centimetre.

[Illustration]

INDEX.

Acid, Acetic, 10

― Citric, 10

― Gallic, 10

― Hydrochloric, 9

― Nitric, 9

― Oxalic, 10

― Phosphoric, 10

― Sulphuric, 9

Action of Lineature, 69

Albert’s Photo-litho Paper, 56

Albumen Process, 64

Angerer & Göschl, 25

Asphalt, 17

― Process, 60

― ― Husnik’s, 60

― ― Valenta’s, 61

Autographic Ink, 7

Autotypy, 67

― Negative, 41

Bartös’ Process, 20, 77

Behaviour of Asphalt on Stone, 8

Cadmium Intensification, 40

Chromate Salts, 48

Coating the Stone, 62

Cold Melting Process, 12

Correcting Negatives, 35

Cyanotype Paper, 24

― ― Bleaching, 24

Dark Room, The, 34

Deep-etching Process, 11

Developer, 37

Developing Ink, 8

Direct Printing, 60

― Transfer, 15

Distance of Lineature, 73

Drawing on Blue Prints, 23

― ― Prepared Paper, 25

Eberle’s Process, 11

Eckstein’s Process, 20

Electric Lamps, 31

Etching the Stone, 10

Failures in Transfers, 58

Fixing, 38

Fox Talbot, 17

Franz’s Paper, 55

Galls, Tincture of, 10

Gelatinizing Paper, 47

General Notes on Photo-lithography, 49

Gold and Mercury Intensifier, 38

Greasy Drawing Materials, 6

Gum Arabic, 10

Half-tone, Breaking up, 20

― Photo-lithography, 67

Hebensperger’s Process, 66

Hübl’s Hydroquinone Intensifier, 38

― Iso Emulsion, 43

Husnik’s Asphalt, 17

― Photo-litho Paper, 53

Hydroquinone Developer, 42

Indirect Transfer, 16

Inking up and Developing, 51

Intensification, 37

Intensifier, Lead, 40

― Mercury, 40

― Metol, 39

― Silver, 40

― Uranium, 40

Iodized Collodion, 37

Isochromatic Emulsion, Albert, 41

― ― Hubl, 43

Lemercier and Lerebours, 16

Line Drawings, 21

Litho Chalk, Hard, 7

― ― Soft, 8

― Stone, 4

Lithogravure, 87

Litho-Heliogravure, 79

Lithography, Theory of, 3

Making Direct Negatives, 36

Mungo, Ponton, 17

Negative for Photo-litho, 34

― Transfer with Paper, 83

Negré, 17

Nicephore, Niépce, 16

Orell and Füssli Process, 20, 75

Photo-Autography, 84

Photo-Litho Transfer, 57

Photometer, 51

Poitevin, 17

Prism, 44

Printing, 62

― on Bichromated Gelatine, 50

Pyramidal Grain Paper, 26

Reproduction of Prints, 27

― Size of, 28

Reversed Negatives, 44

Sacher’s Fish-glue Process, 66

Scamoni’s Process, 12

Scraper Boards, 25

― ― Schäuffelen & Co., 26

Sensitizing Paper, 49

Silver Bath, 37

Stripping Negatives, 45

Studio, The, 30

Tusch, 7

Valenta’s Asphalt, 17

Waterhouse’s Arrowroot Process, 66

Wezel & Naumann, 75

Zinc Plates, 5

― ― Roughened, 6

― ― Oxidized, 6

[Illustration]