This is a solution for weak negatives. Chloro-platinite of potash when obtained commercially should be tested as follows: - (i) 1 drm. of the salt should be soluble in 6 drms. of distilled water. (2) The solution should not be acid. This solution will keep unaltered by light for an almost indefinite period. Very feeble light must be used for coating the paper. To keep the paper flat whilst coating, the edges should be turned under-neath a plate of glass placed upon a table; for larger pieces the paper can be easily clipped to glass plate by wooden clips, or it can be pinned at the corners by drawing pins. For coating a sheet of paper 8 by 10 ins., 30 minims of sensitiser are required, which should be poured into the middle of paper and spread over the surface with a uniform circular motion, by means of a pad composed of a tuft of cotton-wool enclosed in a piece of fine washed muslin. The rubbing should be continued gently for at least three or four minutes. As soon as coated, the sheet should be hung up by two corners to dry, and as soon as the surface moisture has disappeared, the paper should be carefully and quickly dried over a gas burner, or before a stove or fire. The whole success of the process lies in this stage - the drying of the paper; the paper must be absolutely dry. This point is known from the change in colour from lemon to an orange colour, and by the crackle of the paper. Care should be taken not to scorch the paper, or fog will be the result. Between the coating and drying about five minutes must be allowed to elapse in summer and eight or nine minutes in winter. The exposure required for the paper is about one-third of that required for a silver print from the same negative. Absolute dryness, both in the keeping before, during, and after exposure is a sine qua non; the slightest trace of moisture tends to render the paper useless. It should be stored in tubes in which chloride of calcium (anhydrous) is kept to absorb the moisture. The image on the paper is but faintly visible.
The Old Hot-bath Development
Oxalate of potash............ 130 grs.
Distilled water ............ 1 oz.
This solution may be kept as a stock solution, and when required for use must be heated to a temperature of 1700 to 1800 F. Development is effected by passing the print face