Probably at some period of the photographer's career, he or she passes through the P.O.P. stage. " P.O.P." means in short " Printing-Out Paper," and were the initials used by the Ilford Company to describe this process when they placed upon the market a gelatino-chloride paper, at the same price as the albumen papers, which up till that time had been generally used. P.O.P., as commercially known, consists of paper coated with a mixture of silver salts and gelatine, and the great bulk of it is made with a glossy surface. It has excellent keeping qualities, providing it is kept in a cool, dry place. The paper may be purchased in sheets, but the amateur will doubtless prefer the packets cut to the size required for his negatives. Care should be taken not to touch the surface with moist fingers, for any mark made would result in a defect in the finished print.
THE P.O.P. PROCESS.
For those who have not done any photographic work previously a word about printing frames is desirable. Purchase a simple form of frame with the back hinged two-thirds of the way along, so that when examining the print the bulk of the picture may be seen by unfastening one of the springs which hold it in position. The springs should be preferably hinged to lift up, and not turn sideways, for such sideways motion will often move the back and the sensitive paper beneath it. The corners of the frame should be screwed, and if glued, see that none of the glue has formed into ridges along the edge where the negative or glass rests, or a broken plate may be the result. It is a great safeguard if a piece of clean glass of good quality is used as a support for the negative. The back of the frame being removed the negative is placed in it, glass side downwards, and a piece of the P.O.P. laid on it, then a rubber sheet or felt pad, to ensure perfect contact, and afterwards the back of the
PREPARING THE PRINTING FRAME.
frame held by the spring fastenings. Printing from thin negatives may be done in weak light or from dense ones in sunlight, the prints being examined from time to time by weak diffused light to see what progress is being made. Printing should be carried considerably further than desired in the finished print, and the exact amount will be learnt after one or two trials. The printing being finished, if not convenient to tone at once the prints may be transferred back to the original packet and kept for a considerable time.
Before toning, the prints must be washed, and this apparently simple operation should be done with method and care. Use plenty of water, and if running water is not available transfer the prints one by one to a large dish of water, keeping them moving the whole of the time. The silver salts will commence to dissolve out of the prints, making the water milky, and immediately this occurs transfer them to another dish of clean water. These operations should be conducted by artificial light or very weak daylight. When the washing water remains quite clear the prints are ready for toning and the bath is simply compounded as follows : WASHING.
Gold chloride is sold in 15-grain tubes. Buy the best quality (Johnson's). Break the tube by hitting it when between a sheet of notepaper, and dissolve in 15 drams of water. Then each dram contains one grain of gold chloride and it is easily measured. Dissolve the sulphocyanide and then add the gold solution, do not mix them in the reverse order. The bath may be used at once, but is better if mixed twenty-four hours before use. It should not be less than 6o°F.
Use a large dish for toning and plenty of solution. Immerse the prints one by one, seeing that they are perfectly covered and that air-bells do not form on the surface. Keep them moving during the whole time of toning and the colour will gradually change, till finally they are almost blue. For a good purple photographic tone watch till the surface begins to look somewhat blue and no red is apparent when the print is viewed by transmitted light. On the surface the print may appear somewhat overtoned. Then rapidly rinse the prints in several changes of water and transfer to a somewhat weak fixing bath.
The fixing bath is as follows :FIXING.
Keep the prints moving in this solution for ten or fifteen minutes and transfer to running water for thirty minutes.
The prints are dried by placing them face upwards on clean blotting paper or suspending them by clips from a line.