paper the P.O.P. class has the advantage of giving more detail with
marked transparency in the shadows. The operations are more flexible
and the results are as permanent, if not more so, than those on
albumen paper. The paper keeps in good condition for a longer time.
The negative giving the best results with P.O.P. is one having
delicacy rather than vigour, _i.e._, a long scale of gradation of
delicate steps is well rendered. Printing takes place quicker with
P.O.P. than with albumen papers. The cost of paper and materials is
much about the same in both instances.
_Notes._--In the glazed variety of paper the smooth shiny surface is
the sensitive one, and, of course, goes next the negative in the
printing frame. In the matt paper the sensitive side may generally
be known by its tendency to curl inward, _i.e._, the concave or
hollow side is the printing side.
Formalin may be used in place of alum for hardening the gelatine. Of
the usual 40 per cent. solution of formalin take one ounce and
dilute with ten or twelve ounces of water.
Dark spots or specks are frequently due to metallic dust either from
the fingers or in the water. Mounts having sham gold edges or bronze
powders should be banished from the dark-room. Dry "pyro" floating
in the air may also account for spots.
_Rev. F. C. Lambert, M.A._
[Illustration: UNLOADING. A. M. MORRISON.]
_Platinotype Printing._
[Illustration]
Amongst the various printing processes in common use amongst
photographers, platinotype is unique in several respects.
Printing is conducted by daylight in precisely the same manner as
silver printing, but the action of light only suffices to make the
image partially visible. In this respect, platinotype stands, as it
were, midway between what are familiarly termed "print-out"
processes--that is, those in which the image is made completely
visible by daylight, and those in which the action of light is
latent or invisible, such as bromide paper and in the carbon
process.
The distinctive character of the platinotype print, with which,
probably, everyone is so familiar that a platinotype effect almost
amounts to a generic term, is not so much essential to the process,
but has been largely determined by the different kind of papers and
the preparation of those adopted by the manufacturers of platinotype
printing papers.
In the first place, the platinotype print is before anything a matt
surface print, and possesses a certain kind of texture or surface
which gives the finished print an appearance similar to a pencil
drawing or an engraving; an appearance largely assisted by the
characteristic colour of the platinum image, which is black.
The invention and production of platinotype paper is due to Mr.
Willis and the Platinotype Company, and although subsequently there
have been both English and foreign imitators, we may safely confine
our attention to those papers made and supplied by the Platinotype
Company.
As, however, the purpose of this article is to furnish the beginner
with simple working instructions, rather than to describe the
principles of the process, we will at once proceed to say how a
platinotype print is made.
To begin with, platinotype printing is divided into cold-bath
process and hot-bath process. Of the latter we shall speak later on,
but for the present, as being most suitable for the amateur and
beginner, we will consider the cold-bath method. The reason for this
division and the meaning of the name will be abundantly evident
presently.
We first of all procure a tin of paper of the quality marked AA. The
paper is put up in tin cylinders containing twenty-four pieces of
either 1/4-plate or 1/2-plate sizes, or less for larger sizes. It
may, if preferred, be obtained in full-size sheets 20 × 26 inches.
We have now to bear in mind that the paper is sensitive to daylight
to a slightly greater degree than are the silver print-out papers,
and hence, whilst handling the paper, placing it in the printing
frames, or what not, we need to be a little more careful as to how
near the window we bring the paper. At the side of the room furthest
from the window, or with an intervening screen between the paper and
the window, or yet again, with the blind drawn down, we shall be
quite safe in opening our tin of paper and inspecting it.
On removing the lid of the tin we find a false top or cover
hermetically sealing it, which has to be cut through in the manner
becoming customary with various tinned foods and comestibles.
We then find that the paper within is yellow on one side which is
the sensitive side. Within the roll of papers at the bottom of the
tin we shall find a hard irregular lump of some substance wrapped
round with cotton wool. Keep this in the tin and now note its use
from the following:--Platinotype paper is highly susceptible to
moisture and deteriorates under its influence. The air we breathe,
and therefore the air enclosed within the tin case or any other
vessel contains a large amount of moisture, and this moisture would
be taken up by the platinotype paper to its own detriment. The
presence of water or moisture in the atmosphere or in things we
handle, although quite unperceived by us, would be discoverable by
the platinum salts on the paper, which would thus become unfit for
use, hence the only way of preserving it is by placing in the tin
containing the paper some chemical which is even more susceptible to
moisture than platinotype paper. Such a body is calcium chloride,
and this it is which we find wrapped in cotton wool in each tin tube
of paper, or to speak more accurately it is asbestos prepared in a
solution of calcium chloride. So long as that little lump remains
dry and hard we may be quite sure that it has left no moisture in
the air around it for the platinotype paper, and it will go on
drinking it up until it becomes softened by saturation, when it must
be removed and a fresh piece substituted, or it may be restored to
its former condition by drying it on a red-hot shovel, the asbestos
remaining unconsumed.
Whilst perhaps in after practice we may find it possible to relax
our precautions against damp, yet at the outset the necessity of the
utmost caution being observed cannot be too strongly insisted upon.
Out of a very large number of prints representing the beginner's
first attempts at platinotype, by far the greatest number of
failures are due to damp, and this, probably, for want of conception
of the danger to which the paper is exposed. Remember then that
where there is ordinary air there is also abundant moisture, and as
no tin box with a movable lid is air-tight, neither is it
moisture-proof, but in the case of our tin of platinotype paper when
once opened will go on admitting moisture which the calcium chloride
will take up until it can take no more.
After having cut through the inner sealed top of the tin, close up
the little hole in the outer lid where the cutting point is with
sealing wax, next cover the mouth of the tube with a piece of waxed
paper or tinfoil, shut the lid down on to this, and then cover the
junction of the lid with a broad indiarubber band. In this way damp
may be prevented from gaining access to the inside of the tube to a
great extent.
Specially constructed tubes are made which close with an air-tight
stopper and have a false bottom with a perforated partition in which
the calcium chloride may be kept. Such a "calcium-tube," as it is
called, if not an absolute necessity, is a very desirable
acquisition.
If you now take the negative to be printed from and hold it near the
fire or a spirit lamp, it will on becoming warm give off
perceptible moisture, thus showing that it was distinctly damp
before. The negative, therefore, should be dried before being
brought into contact with the platinotype paper.
[Illustration: STREONSALCH. W.J. WARREN.]
The wood printing frame itself, if it has been used for printing in
the open air, should be placed in an oven or held near the fire to
thoroughly dry it.
Having placed the negative and the platinotype paper in the frame in
the ordinary manner, there should next be placed at the back of the
paper a thin sheet of waterproof cloth, vulcanized rubber of the
proper size and thickness being sold for the purpose; this will
prevent damp from penetrating to the paper from the back of the
frame. The frame may now be closed and placed in the light for
printing, and even having taken all these elaborate precautions
against damp it would not be advisable to print out of doors except
in dry weather, nor should the paper be left in the frame longer
than need be, but if it is not proposed to finish the print off at
once, it should be returned as soon as convenient to the security of
the calcium tube.
GENERAL OUTLINE OF THE PROCESS.
Platinotype paper is ordinarily only available for daylight
printing, though the Platinotype Company have introduced a lamp of
special construction and great power, by the use of which daylight
may be dispensed with, and electric light, should it be available,
may be used.
As has been already said, platinotype paper is rather more sensitive
to light than silver paper, and hence takes proportionately less
time to print.
The duration of the exposure to light constitutes the only real
difficulty in platinotype printing, and whilst just at first it may
result in the beginner's meeting with much disappointment, yet
probably, with a little care and watchfulness the trouble will be
surmounted, and sufficient experience gained to secure fairly
uniform success thereafter, before even the first tube of paper has
been used.
The printed image shows on the yellow ground of the sensitized side
as a faint grey, the darkest portions assuming an orange-grey tint,
whilst the lighter parts remain all but invisible.
A little practice will enable one to judge the right depth, that is
to say, how visible the image should be before printing is to be
stopped, but as a rough guide to commence with it may be said that
printing is complete when the image is about half as deep as we
should expect it to be if it were a "print-out" process.
As we shall have occasion to return to the question of printing
presently, we may now pass to the next step in the process.
In twenty-five ounces of hot water dissolve half a pound of best
neutral oxalate of potash, and keep this in a stoppered bottle as
stock solution. What is known as _neutral_ oxalate should be used,
and in order to ensure having a suitable salt it had better be
obtained from a recognised photographic chemist or dealer.
As the above solution becomes cool, a good deal of the oxalate will
probably settle at the bottom in the form of solid crystals; of
these no notice need be taken, for as long as there are undissolved
crystals at the bottom of the bottle we know we have a saturated
solution.
We shall now require a dish of porcelain or enamelled iron, and if
we choose the latter great care must be taken to see that the enamel
is not cracked or blistered, as it will have an injurious effect if
the oxalate of potash solution obtain access to the iron under the
enamel.
As it will be convenient to be able to alter the temperature of the
solution when in this dish at will, a spirit lamp or stove or a
small gas-stove will be a useful, if not an essential addition. Over
such heating apparatus the dish should be supported on an iron
tripod, or by any extemporized substitute.
If a porcelain dish be used, a thin sheet of iron should be placed
first on the tripod stand, and then three or four scraps of iron,
large common iron nails will serve very well, and on these the
porcelain dish is allowed to rest so that it does not come into
direct contact with the iron plate.
The purpose of this is to save the dish from cracking, moreover the
iron plate becomes hot, and retaining a good deal of heat serves as
a kind of accumulator which goes far to maintain the dish and the
contained solution at a uniform temperature for at least a short
time. Even better than this arrangement will be an iron dish filled
with clean dry sand, the porcelain dish to rest on the sand which
retains much heat.
If an enamelled iron dish be employed, these precautions are not so
necessary, though they may still be used with advantage.
Next we shall require another dish or similar vessel into which we
pour a weak solution of hydrochloric acid, the usual proportions
being:--
Water 70 parts
Pure hydrochloric acid 1 part
This constitutes the whole of the very simple apparatus needed, and
we may now proceed to develop our print, which as already described
is exposed to light in a printing frame in the usual manner until
the image appears rather less than half-printed.
DEVELOPMENT OF THE PRINT.
If convenient it would be an advantage to have the above-mentioned
apparatus set up close to the window or other situation where the
printing is actually carried on in order that each print may be
developed and finished off forthwith,; the reason for this will, I
think, appear as we proceed.
Development--that is, the changing of the print from the partially
visible condition to its full degree of intensity--is practically
instantaneous. The image does not gradually attain its maximum
strength as in a negative or bromide print, but does so within a few
seconds of its coming into contact with the oxalate of potash
solution.
[Illustration: Fig. 1.]
Having put into the dish on the tripod stand sufficient of the
saturated solution of oxalate of potash to cover the bottom of the
dish to the depth of half an inch or an inch, we light the lamp or
stove and bring the solution up to a temperature of about 70°
Fahrenheit. This may be tested with a thermometer or may very well
be guessed by touch; we merely require the solution quite warm, but
not so hot as to cause the slightest inconvenience if the fingers
are placed therein. This will be a sufficiently accurate guide as to
temperature.
In case any dust or scum should have accumulated on the surface of
the bath, wipe the surface of the solution with a piece of clean
paper, and now take the first print to be developed in both hands,
giving it a decided curl, or roll it round into a cylinder
_sensitive side out_, so that it naturally takes a curled-up form
(Fig. 1). We now take the print to the dish containing the oxalate
solution without previous washing and without exposing the paper to
the influence of light or moisture, and lowering the edge of the
paper held in the left hand, sensitive side downwards, until it
touches the fluid quickly and smoothly bring the rest of the print
down until the right-hand end finally reaches the solution, then
give it a sliding sort of shake in order to set free any bubbles of
air which may be imprisoned under the paper, and then on raising the
paper again after five to ten seconds, the image will be found to
have come out to the full degree of visibility, which the amount of
exposure had paved the way for.
The paper may be returned to the oxalate bath for a minute or two
longer if it be thought desirable, though only in the case of a very
cold bath is any effect produced on the print by the oxalate after
the first few seconds. The print is then passed _direct_ to the
hydrochloric acid bath, which should be ready in a dish close at
hand, and the print is now practically finished.
Before placing the print in the acid bath it may be noticed that the
portions of the print not affected by light still remain yellow, and
this yellowness the acid bath removes almost at once.
In order to effectually remove the yellow surface (which is the
unacted-upon sensitive salts and hence upon their removal the
permanence of the print depends) three successive applications of
the acid bath should be resorted to, the prints remaining for 5 to
10 minutes in each, and then finally washed in running water for a
quarter-of-an-hour, dried between blotting paper or in any other
manner preferred, and the platinotype print is finished and ready
for mounting.
It should be seen from the foregoing general outline of the process
that for directness, simplicity, and for the short time in which a
finished print may be produced that platinotype stands alone amongst
printing methods.
There are, however, some points needing careful consideration at
each stage of the print's production, and to these we may now pay
attention.
PRACTICAL CONSIDERATIONS AS REGARDS EXPOSURE.
As has already been stated right exposure constitutes the
crux of the whole process; this once mastered the rest of the
performance--development, clearing in acid and washing--is so simple
that the chance of failure is remote.
Hence the greater need of paying especial attention to the question
of exposure or printing.
Obviously, the duration of time of exposure cannot be fixed, not
even to the extent it can be in bromide printing or any other method
of printing with artificial light which may be a definite and
permanent quantity.
The variable quality of the daylight and the density of the negative
are both fluctuating factors in the calculation and hence some means
may advisedly be resorted to for acquiring a sort of exposure index
suitable for each individual negative and every variety of light.
First let it be noted that even with very great over-exposure the
image will not become wholly visible, whilst to the inexperienced
eye but little change takes place in the appearance of the printed
image after the correct exposure has been reached.
If then the print has been over-exposed, the fact is not made
evident until the print is subjected to the influence of the oxalate
developing bath.
To start platinotype work trusting to chance or good fortune to
secure for us good results, means that our whole course will be one
of uncertainty and filled with exasperating disappointments to say
nothing of the amount of paper and material which is certain to be
wasted in unsuccessful efforts.
The reader will probably have learned something of this from his
past experiences of negative exposure, the difficulties of which he
has by now, we may hope, overcome by careful and patient study, or
else if he is not even now undergoing this stage of learning he is
the victim of endless mistakes, every plate exposed is a shot in the
dark with no certainty attending any one of them.
Exposure, however, in platinotype is not so difficult a matter as
that of a dry plate, and the correct exposure with any particular
negative once ascertained, every subsequent print from the same
negative can, by simple mechanical means, be made with the certainty
of its being _an exact facsimile_ of the others.
PRINTING WITH AN ACTINOMETER.
Several kinds of Actinometers are made for sale, the purpose of
which is either to indicate the right exposure of a plate in the
camera or to tell the duration of exposure for papers such as
platinotype or carbon, the image on which is invisible, or nearly
so.
A simple, yet thoroughly efficient meter may be made as
follows:--Cut some fine tissue paper or _papier minéral_ into strips
about a quarter of an inch wide and attach one to a piece of clean
glass 4-1/4 × 3-1/4 with fresh starch or other colourless mountant.
Upon this first strip and exactly over it place a second, but bring
it to within a quarter of an inch of the end of the first, next
place a third strip in like manner a quarter of an inch short of the
second strip, and so on until some seven or eight strips have been
fixed. The combination will now be somewhat as the following drawing
(Fig. 2), thus forming a tissue band which at each quarter-inch is
one thickness more opaque.
[Illustration: Fig. 2.]
In the centre of each strip or increased thickness, paint with
opaque colour, black or red, a letter or figure as in (Fig. 3). On
the back or other side of the glass to which these strips are
attached, paint over or cover with opaque paper all except the space
covered by the strips. Now place the whole in an ordinary 1/4-plate
printing frame, with the paper strips inside, next adjust a piece of
silver paper, albumenized, or gelatine chloride precisely as though
printing from a negative. Close the back and we then have a
thoroughly efficient actinometer.
[Illustration: Fig. 3.]
We now put out our first piece of platinotype paper to print, and
alongside it so as to receive the exact same amount of light, we
place our actinometer.
The first print must admittedly be guess-work.
After an interval of time, which may vary from say fifteen minutes
to an hour according to the amount of light, we will withdraw the
frame containing the platinotype print, and _simultaneously turn the
actinometer over with its face down_, thus stopping its printing
whilst examining the platinotype.
Retiring from the light we examine the progress of printing
precisely as in silver printing, and we shall probably find that the
image on the negative is now faintly visible on the platinotype
paper, impressed in a sort of warm grey colour.
If the darkest portions are of about the tint which we might produce
by shading with an H pencil on a piece of primrose yellow or pale
buff paper, we may reckon that the print has been sufficiently
exposed.
Now refer to the actinometer and see what has taken place on the
silver paper which we put into it. Probably while the platinotype
paper has been reaching the required depth of printing, the silver
paper has also registered the image of the strips of paper, and has
become printed through up to the fourth or fifth step of the tissue
strips, showing on each strip its letter in white. Make a note of
the highest letter visible and proceed to develop the platinotype
print. If upon development the print is weak and grey, lacking depth
or intensity in the deepest shadows, and having blank and detailless
whites for the higher tones, we may reckon that our print is
under-exposed. The letter visible then, _with that particular
negative_ is not sufficient. We then shift the paper in the
actinometer so as to get a fresh portion under the tissue strips, or
we substitute a new piece. We refill the printing frame and print
again until the actinometer registers one, two, or three more steps
and letters, and then try again. If, however, in the first case the
platinotype print upon development gives a heavy dark print, with
the details in shadows blocked up, and the high-lights grey, the
whole possessing an overdone appearance, then in our second attempt
we shall stop printing when the actinometer records some one or two
letters less. But we may be more fortunate in our first attempt, and
the print may be about right. In that case we mark on that negative
in some way the tint or step or letter in the actinometer at which
we arrested action, and henceforth, no matter the time of year, hour
of the day, or latitude, that negative will give a similar print if
stopped in accordance with that memorandum which it bears.
If, however, we do not hit the right exposure the first time, we are
pretty certain to do so the second, or at the most the third time,
and having done so, we have not only an infallible guide for all
subsequent prints from that same negative, but we have also some
sort of index to base our calculations on for other negatives. Thus
if we at once proceed to print from another negative, that is,
before any considerable alteration takes place in the light, we may
by comparing the negatives at least estimate what will probably be
the second negative's printing letter or step on the actinometer.
Sooner or later every negative (especially those from which we
anticipate wanting subsequent prints) should bear either on the
negative itself, or else in a carefully kept register or note book
its correct printing letter.