W. M'Arthur

It is not an easy matter to convince the beginner in photography that the simplest of all printing processes, and probably the most economical, is the platinotype. There is a strong attraction to P. O. P. for the average worker of little experience in watching the fascinating growth of the image. It appears to be such a simple matter to remove the print when the exposure is complete and to pass it through the various solutions.

All this is perfectly true, and given a fair negative, paper which has not been imperfectly stored, toning baths which have been properly compounded, and absolute cleanliness in a chemical sense, there is no obvious reason why every print should not be successful. Yet even the most successful workers reckon upon a percentage of failures, and in the case of beginners the percentage is usually a high one.

In the toning and fixing of gelatino chloride prints, the principles involved are complex and have not been thoroughly elucidated even by those who have brought great knowledge and experience to bear upon the subject. There is, therefore, the less reason for wonder that the photographer working only by empirical rules laid down for his guidance and by the light of nature should make occasional mistakes.

In the case of the platinotype process the problems are simpler, and although the salts with which the paper is coated are easily susceptible to injury and require great skill in their manipulation and preparation, all this does not affect the photographer, who has only to deal with the paper after its manufacture. The paper is coated with a compound of iron and platinum salts, of which the iron alone is sensitive to light, giving an image of a greyish brown tint.

When the. exposed print is floated upon or immersed in a solution of potassium oxalate the iron salt is dissolved, and at the same moment the platinum salt, which is in intimate contact with the iron is, in those parts where the light has acted, reduced to the black or metallic stage, and is held permanently in position, being imbedded in the fibre of the paper. The amount of platinum deposited and, in consequence, the degree of blackness in the image, is regulated by the exposure given.

In the high lights, where the paper is protected by the denser parts of the negative, the action upon the iron is very slight, and the amount of platinum deposited is so small as scarcely to tinge the white paper, while in the shadows the amount deposited may be so great as to become solid black. The finely divided metallic platinum being soluble only in aqua regia (a mixture of nitric and hydrochloric acid) and not at all affected by climatic influences, the image is absolutely permanent, as it can be destroyed only by means which at the same time cause the destruction of the paper. Properly speaking, no fixing bath is required, development and fixation taking place simultaneously; but a clearing bath of dilute acid is necessary to remove the remains of the iron from the paper, and until this is done the paper must not be placed in plain water.

As the paper is easily damaged by moisture - the touch of a damp finger tip would ruin it - it is desirable that the beginner should purchase it in cut sizes. At the same time he should purchase what is known as a calcium-chloride storage tube. This is a canister having a false bottom of perforated metal, between which and the true bottom a piece of asbestos saturated with calcium chloride solution and dried, is stored. Calcium-chloride greedily absorbs moisture, and in doing so keeps the paper absolutely dry. The joints of the lid and the bottom are damp-proof, either by rings of india-rubber fitted to the joints in some patterns, or applied in the form of rubber bands outside the joints in others. A very efficient storage tube can be had in the "new" pattern for small sizes at a lower price.

On examining the tin in which the paper is sent out it will be seen that the cover is securely sealed by the label. On cutting this and removing the cover the true lid is disclosed underneath and this latter is soldered down, preserving the paper perfectly for a very long time. A cutter will be found inside the cover, and by sliding this as far as it will go, replacing the cover on the tube and turning it round with a little pressure, the true lid is cut out. The ragged edges left after cutting should be smoothed down level with the inside of the tube and the roll of cut sheets enclosed in their wrappers drawn out and trans-erred to the storage tube - together with a supply of calcium-chloride.

The paper is as sensitive to damp as to light, and if the cover of the tube were not sealed with rubber bands there would be a strong possibility of the paper being spoiled within a very few hours. Properly stored the paper will keep in good condition for many months, but if the tube is repeatedly opened, the calcium-chloride should be occasionally examined, and if it is at all damp it should be removed from the outer wrapper and dried. This may be done by putting it upon a piece of thin iron and placing it on the fire till all moisture has been driven off. Unless the rubber bands fit closely there is always a risk of moisture creeping into the tube.

The preparations for printing are very similar to those adopted in printing upon any other photographic paper, except that additional precautions should be taken against damp. It is well to make a point of drying the printing frames - if they have been used in bad weather - by storing them for some hours in a warm dry room, or, if they are wanted in a hurry, by drying them near the kitchen fire. Care must be taken not to overheat them or they may warp and so cause the negatives to break. The negatives should be dried face upwards over the gas flame or in front of a tire till they are warm to the touch and till the moisture which collects on the glass side has been driven off. Sheets of thin india-rubber are sold as excluders of damp from the printing frames and are most useful, but these also should be dried before use. Spoiled celluloid film negatives from the negatives from which the gelatine has been cleaned off serve the same purpose. It is desirable that all negatives used in platinotype printing should be coated with waterproof varnish; not that there is the same risk of them becoming stained as when printing on P. O. P., but because gelatin absorbs moisture, and paper which is printed in contact with damp negatives will have a tendency to give muddy prints.

The hinged back of the printing frame having been removed and the negatives fitted in, film side upwards, the blinds in the room should be drawn, or the operation conducted at some distance from the window, as the paper is distinctly more sensitive to light than is P. O. P. The tube is then opened and one sheet of paper taken out. It will be noticed that the face side is a bright yellow, the back being white. The paper is then laid with the yellow side in contact with the film or face side of the negative and the back of the frame replaced and fastened down. The storage tube should be closed at once and the rubber bands replaced.

Practically the only thing to be learned in platinotype printing is the depth to which the image should be carried, but as the image is fainter in tint than that on a piece of print-out silver paper, and in a color to which the beginner is unaccustomed, a few trials will have to be made before a correct judgment can be formed. To acquire this power of judgment speedily and economically it is a good plan to cut one sheet of paper into four strips and to print these one at a time. While one strip is being printed the others should be kept in the storage tube.

The printing frame" should be placed in a good light, though not in direct sunlight, for the more quickly the prints are made the less risk is there of the paper becoming damp. With a negative of good color and reasonable density printing takes place very quickly. In a few minutes the frame should be taken indoors and one-half of the back opened to permit the print to be examined.

The image, as previously stated, is of a grayish brown tint on a yellow ground, and all detail that is to appear in the finished print should be visible, though faintly, after exposure. If the exposure is judged to be sufficient the strip may be cut in half, one part developed and the other kept in the storage tube as a guide when printing the other strips. - Photography, London.