CRYSTOLEUMS Photographs coloured to give the appearance of direct paintings upon glass ; known also as chromo-photographs. The system of colouring is about two centuries old, and, before the days of photography, engravings and prints were used as a base, the process being known generally as mezzotinto painting. The advent of photo graphic prints on paper did much to revive the interest in colouring processes. A modern crystoleum print properly finished looks, as is intended, like a painting upon glass, but actually a transparent photograph comes between the colouring and the glass. The diagram shows the construction of a crystoleum photograph. A is the front glass, on which a photograph B is pasted face downwards. When dry the photo graph is made transparent, and delicate details coloured with ordinary oil colours, but the broad masses of colour are not put on. Another glass D, of the same size and shape as A, is put at the back, but is prevented from touching the photograph by means of strips of paper H, which leave a small space at C. On the back E of the second glass are painted the broad masses of colour. The whole is backed up with a piece of flat cardboard or other backing G, leaving d. space P. When viewed from the front the colours are seen through the transparent photograph, and the whole has the appearance of a delicately painted picture upon glass.
The working details are as follow : A suitable print is made upon albumen paper, which is the only photographic paper suitable, it being thin and tough. The print is placed in hot water until it becomes quite flaccid, and is then made surface dry by pressure between clean white blotting-paper. A piece of convexo-concave glass (flat glasses are not so suitable), sold specially for the purpose, is then made quite clean, and its concave side coated with clear starch paste or warm gelatine. The damp print is laid paper side downwards upon a flat piece of glass, and its face is coated with the adhesive selected. The print is then placed face downwards in contact with the inner (concave) and prepared surface of the glass, and pressed into close contact. The surplus paste must be removed from between the print and the glass, this being accomplished best by laying a piece of wet parchment over the back of the damp print, pressing out the hesive with a knife handle or toothbrush handle. The paste must be expelled, all air-bubbles, by a not too firm pressure, which must be worked always from the centre of the print to the extreme margin. When in perfect tact the parchment is taken away, the back of the print wiped free from any fluous adhesive, and the whole put aside to dry thoroughly. The correct mounting of the picture is most important, as any errors will spoil the effect. When dry the print must be made transparent, and this is accomplished in one of two ways—namely : (I) Rub the back of the print with paper in order to remove as much of the paper as possible (the actual picture being, of course, underneath, next to the glass) ; a medium glasspaper is used at first, followed with a very fine one in order to remove all scratches, and to lessen the possibility of suddenly penetrating the actual picture on the albumen. When the
bulk of the paper has been evenly rubbed away, the glass side of the picture is warmed before a fire, or over a gas-stove, and at the same time a piece of paraffin wax is rubbed on the paper side of the print, the object being to saturate the picture with warm wax. When the print appears equally transparent all over, all fluous wax is removed with a piece of flannel and the picture allowed to cool. When cold the wax may be further polished, and if not evenly transparent it must again be papered on the dense parts and waxed again. (2) The alternative process consists in leaving the paper print of its original thickness and making it transparent by rubbing into it a solution of oz. of Canada balsam in 3 oz. of either benzene or chloroform, the former being the cheaper. Another solution for the purpose is Canada balsam 2+ oz., paraffin wax r oz., and white wax x oz heated together and used in the same way as the wax in the first method.
Upon the print prepared as described all the fine details are now coloured, these includ ing the lips, eyes, jewellery, etc. A finely pointed sable brush is used, and ordinary oil colours slightly diluted with megilp. After the colouring, the second glass is put on at the back and bound by the edges to the first one to keep it in position. It must be as close as possible to the first glass, but not touching, and it may be kept from contact by sticking two or three thicknesses of stamp edging along the edges of the front of the second glass ; or a narrow strip of thin cardboard may be used in the same way. The colouring on the second glass may be very crude, the masses of colour being put on the back and care being taken not to overlap the outlines. No details or lights and shades are wanted, as they appear in the picture itself, but body colours only are wanted, these being mixed with a proportion of flake white. The colour already in the print must be considered ; consequently, to picture fair hair in a portrait, white tinted with yellow will serve. Upon view ing the picture from the front (holding it over white paper), one can easily judge whether the colouring is correct or not. If not, it may be corrected or removed with a rag and turpentine.
The final operation consists in attaching a piece of white cardboard to the back of the second glass and binding the whole together by means of narrow paper strips, and then framing. Fancy gilt frames are the most suitable, but obviously any may be used. Special solutions for mount ing the pictures, making them transparent, and for preserving the transparency and colouring, are articles of commerce. P. R. S.