PHOTO-LITHOGRAPHY--_continued_
A Copying Table--Exposure--Illumination--Photo-litho
Transfers--The Paper--Printing--Developing--A Direct
Process.
To discuss the respective merits of the "wet" collodion, collodion
emulsion, and dry-plate processes lies beyond the province of this work,
as does also a detailed description of the operations involved.
The processes are purely photographic, and have already been presented
to the craft in various forms. It is, moreover, almost impossible to
bring within the limits of a single chapter anything approaching to a
comprehensive record of the multitudinous details upon which process
photography is based. All that can be attempted is to take one or two
outstanding features which suggest a few useful hints.
The original or copy for reproduction must be on the same optical plane
as the sensitive plate in the camera, _i.e._ they must be absolutely
parallel with each other. There are several ways of ensuring this. The
most convenient method is to use a copying table and board similar to
Fig. 31. With such an arrangement as this direct copying can be attained
through the lens, or the camera can be turned half-way round, and the
image reversed by means of a mirror or prism attachment. The chief
advantage of such an arrangement is, that the position of the camera can
be altered at will without affecting the relative positions of the plate
and copy.
[Illustration: FIG. 31.]
Correct exposure and sufficient illumination of the copy are important
factors in photographic reproductions of any kind, but they are of
infinitely greater importance when applied to photo-process
reproduction. One is, to a certain extent, dependent upon the other. The
former must of necessity be controlled by the latter; yet no amount of
exposure will compensate for defective illumination. Where artificial
light is employed the advantage of using two lights is obviously great.
Apart from the greater brilliancy and intensity of the light, the
illumination of the copy is more evenly distributed. In scraper-board
copies no shadows are thrown from the embossed dots or lines, and the
granular texture of grained papers is almost entirely eliminated.
A bichromated, gelatine paper can be obtained by coating a hard writing
paper of medium thickness with a gelatinous solution consisting of 1 oz.
of gelatine and 1 oz. of water, and afterwards sensitising it with
bichromate of potassium. It is advisable, however, to use the commercial
varieties of coated paper, and to sensitise it as it is required.
The sensitising solution can be prepared by dissolving 1 oz. of
bichromate of potassium in 20 fluid oz. of water. Add to this sufficient
ammonia to give it a bright orange tinge. Keep this solution at a
temperature of 60° Fahr., and float the paper on it for about one
minute. Pin or clip the paper to a board or squeeze it to glass, and dry
in a dark room.
Print this paper under the negative in a diffused light until the design
appears in a rich golden-brown colour, when the exposure may be regarded
as sufficient. The time allowed for such an exposure will, of course,
vary according to the quality of the negative and the intensity of the
light.
A development of the print may now be proceeded with in the following
manner.
Thin down a little transfer ink with turpentine and distribute it
evenly on a composition roller. Roll up the print until it is completely
covered with an exceedingly fine film of ink, after which allow the
turpentine to evaporate. Immerse the transfer in tepid water for about
10 minutes, and then rub it gently with a piece of cotton lint
previously soaked in water, until the superfluous ink is removed and the
design stands out clean and sharp.
The transference of the print to stone can be accomplished in the usual
lithographic manner. The chief points to be observed are, to allow
sufficient time for printing, and to ink up the transfer with the
thinnest possible film of ink.
A photo print can be made direct on the zinc or aluminium plate, and by
a slight modification of the photo-engraving process it can be developed
according to lithographic methods.
It is impossible to introduce an intermediate process without, in some
manner at least, depreciating the quality of the work. In a direct photo
print on zinc, or, in fact, on any suitable printing surface, the finer
qualities of the work are much more likely to be retained than when a
transfer print is made under the negative and afterwards transferred in
the usual manner.
Coat a finely grained zinc plate with sensitised asphalt solution and
expose it under a negative for about 4-1/2 minutes in direct sunlight,
and from 12 to 15 minutes in a diffused light. The action of light on
the asphalt solution is to render it insoluble in turpentine, so that if
a sufficiently exposed plate is immersed in pure turpentine the lines,
etc., of the design, being of course represented by clear lines in the
negative, will remain intact, while the surrounding portions will be
dissolved and washed away. After development wash the plate freely in
water, and dry it by fanning or with a pair of bellows. Let it stand for
about 10 minutes and then slightly etch it with a very weak solution of
nitric acid. Cover the work with strong, fresh gum, and dry it
thoroughly and quickly. Remove the gum and "rub up" the design with
black ink in the usual way. Wash, dry, and dust over with French chalk.
The plate can then be prepared in the manner described in Chap. XI. page
61.
THE END
INDEX
PAGE
Adjusting pressure in machine, 38
Adjusting stones in machine, 37
Air drying--tin printing, 78, 79
Alum, 27
Aluminium plates, 57
Aluminium plates--
Alterations, 62
Direct photo, 58, 85, 100
Etching, 61
Machining, 65
Printing bed, 65
Rolling up, 60
Sensitising, 99
Transferring, 59
Aluminium rotary machine, 65, 66
American printers, 53
Asphalt solution, 100
Bavarian limestone, 1, 2
Blocking out, 54, 55
Blue tinge, 70, 77
Boxwood scraper, 20
Brake cylinder, 38
Bronze printing, 49
Cam motion, 21
Canada balsam, 54
Castor oil, 28
Cause and effect, 2
Ceramic decoration, 55
Chalk drawings, 25, 26
Chemical affinity, 2
Clean stones, 3
Cohesion in printing ink, 54
Colour and design, 48
Changes, 70
Mixing, 30
Printing, 47
Registration, 48
Sequence, 48, 50, 76
Super-position, 48, 81
Transparencies, 55
Colours, standard, 55
Copperplate press, 17
Printing, 17-19
Stove, 18
Copy, photo-litho, 89
Copying table, 96
Crayon or chalk drawing, 8
Crayon work, 89, 90
Cylinder press, 21
Damping rollers, 40
Design, 24
Design, inverted, 68
Design, suitable, 80
Development, photo print, 99
Direct impression, A, 72
Discoloration, 70
Distortion, 49, 68, 75
Dryers, 71
Drying colours, 50, 71
Drying metal plates, 77, 78
Drying racks, 78, 79
Duplication of design, 30, 31
Effect of pinks and greys, 49
Effects in tin-plate printing, 81
Elastic bedding, 22, 23
Electricity, 46
Elements of lithography, 2
Embossed lines, 89
Plates, 82
Embossing dies, 82, 83
Enamelled paper, 51
Etching, 25, 26
Evolution of tin-plate printing, 67
Exposure, 99
Fine etching, 95
French chalk, 71, 76
Skins, 28
Friction glazed paper, 51
Glass muller, 6
Gold lacquer, 77, 81
Gold printing, 49
Grain, natural, 87
Graining stones, 5, 6
Grinding stones, 4-6
Gripper, 42
Gripper margins, 31
Grit, 43
Half-tone, photo-litho, 86
Halligan machine, 34-36
Hand labour and machine, 3
Lever, 21
Roller, 28
High lights, 89
Homogeneity of stones, 2
Illumination of copy, 99
Impression, 27
Impression, size of, 75
Impression, solid, 46
Inking rollers, 39
Inks, printing, 52-56
Tin-plate printing, 69-71
Transfer, 8-11
Inverted design, 68
Key formes, 27, 41
Lacquer, peculiar feature of, 83
Lacquer, tin-plate, 77
Lamp-black, 28
Leather dressing, 22
Level surfaces, 3
Levelling stones, 37
Line, photo-litho, 85
Linoleum, 23
Linseed oil, 52, 53
Litho press for copperplate, 19
Litho press, mechanical principles, 20, 21
Litho press, pressure, 20
Litho varnish, 52, 53
Magnesia, 71
Mechanical affinity, 2
Metal plates, 57
Method, 45
Modification of colour sequence, 48
Motor driving, 46
Nap roller, 28
Natural grain, 87
Negative, 88
Offsets, 27, 28
Oriental blue tinge, 70, 77
Original stones, 30
Outline forme, 48
Packing cylinder, 21
Paper, enamelled, 51
Well seasoned, 49-51
Pen and ink sketches, 89
Pen and scraper effects, 90
Photo litho--
Copy, 89
Development, 99, 100
Direct, 85
Half-tone, 86
Inception of, 84
Line, 85
Printing, 99
Transfer, 85
Transfer paper, 99
Plumbago, 22
Porosity of stones, 2
Preparation of stones, 2-7
Preparing designs, 24, 25
Pressure alterations, 43
Excessive, 37
Litho press, 20
Peculiarities, 75, 76
Printing inks, 52
Cohesion of, 54
Printing medium, 1
Proving, 29, 30
Recipes, transfer inks, 9-11
Transfer papers, 13-15
Reciprocal movement, 72
Reducing medium, 53, 54
Register lines, 29, 30
Registration, 29, 41
Registration of colour, 48
Remedy, A, 71
Re-transferring, 31
Rotary machine, printing, 65, 66
Rubber blanket, 72-75
Resilience of, 76
Scraper, 20-22
Scraper boards, 89, 90
Scratches, 5
Screen effect, 86
Screen photo, 86
Senefelder, 2
Sensitising solution, 99
Sequence of colour, 48
Set off, 71
Shading mediums, 90
Shadow, 89
Sheen of metal plate, 70
Side lay, 42
Silver print, 89
Slogger, 38
Sludge, 5
Solid oil, 53
Speed, 36, 37, 46
Speed cones, 46
Standard colours, 55
Stone-planing machine, 3, 4
Stone-polishing machine, 4, 5
Stoving tin-plates, 78
Transferred prints, 69
Substitutes for stone, 57
Suggestion, A, 49
Super-position of colours, 48
Tooth of grained stones, 7
Of metal plates, 58
Transfer inks--
Active principle of, 8, 9
Copperplate, 10, 11
Extra powerful, 11
Plate, 9
Stone to stone, 10
Writing, 9, 10
Transfer paper--
Autographic, 14
Copperplate, 14, 15
Diaphanic, 16
Grained, 15, 16
Photo-litho, 16, 99
Specific value of, 12
Stone to stone, 13
Transparent, 13, 14
Varnished, 13
Transfer printing, 55
Transferring, 32, 33, 100
Transparencies, 55
Trimming paper, 43
Tympan, 21, 22
V-shaped edge, 22
Varnish, litho, 52, 53
Vaseline, 54
Venetian red, 28
Water of Ayr stone, 25
White printing, 70, 76, 77
Zinc plates, 57
Zinc plates--
Alterations, 62
De-polishing, 58
Etching, 61
Graining, 58
Machining, 65
Photo, direct, 58, 85, 99
Printing bed, 65
Rolling up, 60
Sensitising, 99
Transferring to, 59
_Printed by_ MORRISON & GIBB LIMITED, _Edinburgh_
* * * * *
Transcriber's Notes:
Obvious punctuation errors were repaired.
Both "overestimate" and "over-estimated" appear in the original text.
The following additional corrections were made to the text:
Page 46, "therein" changed to "herein"
(are discussed herein which,)
Page 48, "superposition" changed to "super-position"
(the super-position of blues,)
Page 70, word "the" added to text
(At the same time,)
Page 102, "12" changed to "1, 2"
(Bavarian limestone, 1, 2)
Page 102, "discs" changed to "dies"
(Embossing dies, 82, 83)
Page 103, "61" changed to "51"
(Paper, enamelled, 51)
Page 104, "4" changed to "11"
(Extra powerful, 11)
Page 104, "Depolishing" changed to "De-polishing" to match text
(De-polishing, 58)