6th. - The sensitive papers generally improve in condition by being kept a few weeks after manufacture. They remain in good condition for a considerable time if kept in a cool, dry place, in the special storage tubes.
The bottom of the developing dish should be covered with the developing solution to the depth of at least one-half of an inch.
After the prints have been developed put the solution, without filtering, into a bottle for future use ; it should not be exposed to a strong light. When next developing the solution will be found to be nearly clear, but, of course, tinted by previous use. If this clear solution be not sufficient for use, add to it some fresh developing solution. It is a safe plan always to keep the " bath-solution "up to its original bulk by this means. A little suspended matter in the bath is not of any consequence.
With weak negatives the addition of a little bichromate of potash to the bath gives brighter prints. The amount necessary depends upon the degree of " cutting-out " required, the strength of the developer, and particularly its temperature. The stronger the developer and the higher the temperature the more bichromate is necessary. At 160 degrees Fah. the salt has little or no effect. One grain of the solid to every 10 ozs. of a cold developer makes a distinct difference. The de-oxidizing action of the salt present in such minute quantities, gradually wears off, which may be compensated by the very cautious addition of fresh bichromate.
CLEARING AND WASHING.
To clear the developed prints : these must be washed in a series of baths (not less than three) of a weak solution of hydrochloric acid. This solution is made by mixing 1 part of hydrochloric acid with 60 parts of water. The specific gravity of the acid should be not less than 1.16 ; if lower, more acid should be used. The acid should be colourless. On no account should commercial hydrochloric or muriatic acid be used. Citric acid, in proportion of 1 ounce to 20 ounces of water may be used. This softens the paper in less degree than does the hydrochloric acid. A white opalescence of the bath shows necessity for more acid.
As soon as the print has been removed from the developing dish it must be immersed face downwards in the first bath of this acid, contained in a porcelain dish, in which it should remain about five minutes ; meanwhile, other prints follow as they are developed. The prints must then be removed to a second acid bath for about ten minutes ; afterwards to a third bath for about fifteen minutes. While the prints remain in these acid baths they should be moved so that the solution has free access to their surfaces, but care should be taken not to abrade them by undue friction. It is impossible to affect the image per se by leaving the prints for a long time in the acid bath ; but such treatment, continued for an hour or more, tends to make the paper soft and porous, and to damage the surface of the paper.
The prints should not communicate to the last acid bath the slightest tinge of colour. If the bath, after the prints have been washed in it, does not remain as colourless as water when a depth of fully two inches is viewed in full daylight, the prints should be treated to yet another acid bath.
Pure hydrochloric acid must be used.
If commercial or muriatic acid be used, the prints will be discoloured and turn yellow.
For each batch of prints fresh acid baths must be used.
After the prints have passed through the acid-baths, they should be well washed in three changes of water during about a quarter-of-an-hour. It is advisable to add a pinch of washing soda to the second washing water to neutralize any acid remaining in the print. Do not use water that contains iron, as it tends to turn paper yellow. Soft water is the best for this purpose.
Use a mountant which does not stain or show through the print. Gelatine alone is not suitable, except for thick paper. Thick cold starch is a good mountant or the adhesive dry mounting process will be found very satisfactory.
INSTRUCTIONS FOR THE USE OF THE SEPIA PAPER.
With few exceptions the method of carrying out the operations is the same as for the " black " kinds of platinotype paper. The following points should be attended to : The " Sepia " paper is more easily affected by faint light, and, therefore, increased care must be taken when printing.
The following developer, specially prepared by the Company, is particularly recommended : 1/2 lb. sepia developing salts dissolved in 32 ozs. of hot water (distilled or rain water).