The probabilities being in favour of an increased use of silver citro-chloride mixed with gelatine, for the purpose of obtaining positives printed out for enlarging, the •lantern, opal, or paper, it may not be considered out of place to say something about the prints so obtained. Not that the ordinary methods of toning paper prints are unsuitable, or that any very especial care need be observed beyond the usual precautions; still, without some definite formulae for guidance, there is a possibility some difficulty may be experienced in obtaining the colour desired.
Ammonium sulphocyanate 1 dr.
Water ........ 1 pint
Gold terchloride .. .. 1 gr.
Upon adding the gold, it is converted into a sulphocyanate, which will be seen to have a red colour. The precipitate, however, dissolves in the excess of sulphocyanate, and is then ready for use.
Washing before toning is dependent on the formulae employed in making the emulsion; in most cases it will be found advisable. Toning action is first seen at the edges, by the colour changing to a yellowish brown; soon the whole print assumes a sepia tint, then purple, and finally blue-black, the usual time occupied in these changes being less than 5 minutes. The print should then be transferred to another dish containing a plain solution of amnionic sulphocyanate (2 dr. of the salt in 1 pint of water), where it may remain 5-10 minutes, after which it should be placed in weak hypo (1 : 10) until the soluble chloride is dissolved. Ammonium sulphocyanate alone will be found to fix a plate or paper print made with silver citro-chloride emulsion, but hypo is cheaper and quicker. Should the plates cr paper be inclined to frill, place them in saturated chrome alum solution after toning; this in no way affects the colour or purity of the whites. Washing is the same as with other gelatine plates and silver prints. (W. M. Ashman.)