PhotoHistory

From: THE BARNET BOOK OF PHOTOGRAPHY

Platinotype Printing

By A. Horsley Hinton, 1898

SOME POINTS TO BE CONSIDERED WITH REGARD TO DEVELOPMENT

To avoid confusion it will be well to repeat here that at present we are only considering the practice of what is known as the cold-bath paper. This term is applied only in a comparative sense. The older hot-bath process requires the developing bath to be raised to a temperature of about 170 degrees F., whereas the best temperature for the cold process is about 70 degrees F. or even less; nevertheless, the cold-bath paper may be developed in an oxalate bath of 170 degrees or even hotter, so also it may be developed in a solution which is quite cold. The result of altering the temperature is two-fold and may be stated thus: The colder the bath, the colder the color, that is, the bluer the grays and blacks, also development is slower and takes longer, and the contrasts harder. The hotter the bath the warmer or browner the color of the print; the more sudden the development and the greater the amount of half-tone and consequent softer contrasts.

With these maxims in mind some amount of control may be exercised over the prints produced, especially as regards arresting development at any point desired if a cold developer be used, but in such case the print must be instantly removed to and plunged into the acid bath, until which immersion development continues, even after the print has been removed from the bath.

Development, as a general rule, should be conducted in feeble daylight or artificial light.

Development need not take place immediately, but at some subsequent time, provided the prints be meanwhile stored in a calcium tube and in every way rigorously protected from damp.

The proportions which I have given for the oxalate of potash bath represent the standard developer as given by the makers of the paper for the hot-bath papers, and they recommend that this be diluted to about half strength for cold-bath papers. Personally, I use it at full strength for the cold process, and see no reason for diluting it.

It may be said that such a course is calculated to give strong, vigorous prints, for generally speaking, the stronger the bath, the stronger the contrasts of the print. The difference, however, produced by altering the strength of the bath is not very great.

There are two alternatives to the oxalate of potash developer, both possessing certain, if not very strongly marked characteristics. The first of these is known as the “D” salts. These are sold in tins by the Platinotype Company, and consist of a loose admixture of certain salts, and hence it is essential that the entire contents of a half-pound tin be dissolved at once and kept thus as a stock solution.

The proportions to be used are as follows: Dissolve 1 pound of D salts in 50 ounces of water, and then take equal portions of this solution and water, in other words, dilute it to half strength.

The “D” salts are said to give colder colors and more half-tone, but the color derived from development on the first-named oxalate bath may be made colder by adding to 20 parts of developer one part of a saturated solution of oxalic acid, in like manner slightly warmer color may be obtained if the oxalate bath be made alkaline by the addition of carbonate of potash, but only just enough should be added to turn a red litmus test paper blue.

If prints developed on D salts should appear mealy or granulated, the bath should be strengthened or used at the full strength of the stock solution (salts one pound to water 50 ounces.) Another developer, the effect of which is to minimize half-tone and increase the vigor of the contrasts, and so give very brilliant and even hard blacks and whites, is as follows:

Oxalate of potash 16 ozs.
Phosphate of potash 4 ozs.
Sulphate of potash 1 oz.
Water 120 ozs.

This should be made with hot water, and to get the full advantage of its contrast-giving powers, used quite cold. Development will then probably take one or two minutes, but can be arrested sooner when the desired effect is attained.

It may now be as well to enumerate and describe the various kinds of platinotype paper obtainable, and whilst the general treatment of them all is the same as described in the foregoing, some special recommendations may be made in each case.

The papers for the Cold-Bath process are two called respectively AA and CC. AA is a smooth surface paper and is the kind usually employed for portraiture and general small work. CC is a heavier, stronger paper with a surface similar to stout cartridge or drawing paper. For pictorial work and for landscapes, also for large portraits or heads this paper is eminently suitable. Next we have the papers for Hot-Bath process, to be presently described. These are firstly A and C, both precisely the same in character as the AA and CC just referred to, but intended to be developed in a bath at high temperature. These four kinds of paper all yield a picture of the normal platinotype black color, the black tending to cooler or warmer tints according to slight modifications of treatment, but it is also possible to produce a platinotype print of a rich sepia brown by using the papers S and RS these both in substance and character corresponding with AA or A and CC or C respectively. Thus we have a thin smooth and a thick rough paper for each Cold bath, Hot bath, and for Sepia printing.

DEVELOPMENT OF HOT-BATH AND SEPIA PAPERS

With the Hot-Bath papers perhaps the precautions against damp should be rather more stringent than for Cold-Bath papers, certainly they may not be relaxed, and in the sepia papers, S and RS, there seems to be even greater susceptibility still, but for this, printing and development are performed precisely as already described, but the temperature of the oxalate bath should not be less than 150 to 170 degrees F., whilst in some cases it may be convenient to raise it still higher. The oxalate solution should, moreover, always be at full strength, namely, 1/2 pound in 25 ounces of water or thereabouts; a much more diluted bath will result in granular prints. As a general rule the color of A and C prints is a rather browner black than their cold-bath equivalents AA and CC with also rather softer contrasts.

Development takes place in shorter time than with cold-bath papers, and is indeed so instantaneous that any control is next to impossible. On this account, rather more dexterity will be required in development, that is to say, between the time that one end of the print touches the developer and the rest of the print is brought into contact with it, the shortest possible time should elapse. There must be no hesitation, the whole surface must be brought down gradually but swiftly, and accompanied by a sliding movement in order to squeeze out or wipe out any air bubbles which might cling to the surface of the paper. If this be not done evenly and continuously, it is more than likely that there will be marks of unequal development on the surface.

It is no uncommon thing for the tyro to let the print hover over the bath before giving it its plunge in the hot solution, but in so doing it should be remembered that he is submitting it to the direct action of the steam which the bath is giving off, and so exposing it to damp.

Whilst with prints of  1/2 plate size and under it may be sufficient to hold the print by one corner and wipe it across the surface of the solution, pressing it down with the fingers of the other hand, with larger sizes it will be well to cultivate a little trick in manipulation, in which the left hand brings one end of the print into contact with the bath, whilst the right hand holds the opposite end above and well back — the left hand will next be moved sideways, drawing the print with it along the surface of the bath, the right hand following but simultaneously lowering the whole of the print — thus the solution attacks the print smoothly and continuously, whilst the air is pressed out in the opposite direction. Instantly the entire print is floating on the bath it should be moved about a little, as a further means of disengaging any air bubbles.

As far as possible, prevent the developer from flowing over the back of the print, but this will be a far less evil than not bringing the whole printed surface immediately and at one stroke on to the developer. The print is next passed direct and without intermediate washing into the hydrochloric acid bath, as already described.

The sepia papers, S and RS, are both hot-bath papers, and no special instructions need to be given as regards development, except that to get the full benefit of the sepia tint and secure a fine rich bright color, the Special Sepia Solution prepared and supplied by the Platinotype Company should be employed in the developer.

Of this, one or two drams should be added to each ounce of oxalate bath, either before heating it in the dish or afterwards and just before floating the prints. In the latter case stir the whole so as to get it equally mixed, and wipe the surface to remove any scum.

A good substitute for the bath as above prepared for sepia prints may be made by adding one part of saturated solution of oxalic acid to each ten parts of oxalate of potash solution. The Sepia papers are rather more sensitive to light than the Black papers, and hence all operations should be conducted in very subdued daylight, a precaution even extending to the first acid bath.

The bath containing the special solution should be used for sepia prints only, and when done with kept in a separate bottle for future use, but the bottle must be kept from the light, and the sediment which will fall should be left undisturbed at the bottom of the bottle or filtered out, and the dish used for sepia development should be well washed before using it for black prints.

Opinions seem to differ as to the wisdom of keeping old developing baths, but as far as my own experience goes I use the oxalate solution for black prints again and again, taking no heed of its discolored condition.

After developing, the bath is poured into the stock bottle, and so long as undissolved crystals remain at the bottom of the bottle hot water may be added from time to time to make up the loss occasioned by spilling and waste, thus the stock solution is always a combination of old and freshly-dissolved oxalate; I have had one large jar of solution thus in very frequent use for over twelve months, a greenish-black encrustation gradually accumulating at the bottom without detriment.