CHINA, PHOTOGRAPHS ON There are several methods of printing photo graphs upon china, crockery, opal, etc. For objects where the picture is to be viewed by reflected and not transmitted light, the carbon, process (which see) is perhaps the best ; tissue of any colour may of course be used, and the pic ture, after being printed upon the tissue, is transferred and developed upon the china sup port, after the latter has been properly prepared with a suitable substratum. By this process it is an easy matter to transfer photographs upon curved surfaces. The ceramic process (which see) is more difficult, but the results are abso lutely permanent and will permit of any amount of washing.
The blue-print (ferroprussiate) process is simple, and is often employed for producing pictures upon china and glass. It will be neces sary to give the article a coating of gelatine to serve as a vehicle for holding the sensitive solu tions, the blue-print being a direct printing and not a transferring process, as carbon. A suit able gelatine substratum may be made by soaking 22 grs. of Nelson's No. i gelatine in i oz of water and melting by the aid of heat, afterwards filtering while hot. The solution, when warm (13o° P. or C.), is coated as evenly as possible upon the part of the article to be printed upon, and then set aside to cool. The prepared part is then sensitised as if it were paper, and when dry it is ready for printing upon.
Collodion has also been recommended as a vehicle for the blue sensitising solution, and the results are perhaps more permanent. The formula is : pyroxyline (high temperature) 120 grs., methylated alcohol (.820) 6 oz., and methylated ether 5 oz. Mix a day or two before using, allow to settle, coat the article with the mixture, and when set sensitise with the " blue print " mixture. Substratums of collodion have been known to peel off, and to prevent this the places where the edge of the collodion is to come should be treated before coating with a solution of indiarubber in benzole.
Ordinary glass negatives can only be employed for printing when the surface is flat ; on curved surfaces film negatives may be kept in contact by means of elastic bands, as shown in the illus tration, or by means of gummed paper at the corners. As it is not desirable to remove the negative from the vase for the purpose of exam ing the progress of printing, there must be something left to chance, or an actinometer must be used. It is advisable to varnish such pictures when dry. Blue pictures may be toned to a different colour by any of the methods advocated under the heading " Blue-print Pro cess," sub-heading " Toning Blue-prints."