The crystoleum was a modern application of an ancient technique where colour was applied behind a print or lithograph which had been rendered transparent with wax or varnish. In the case of the crystoleum, also known as a chromo-photograph, an albumen print was pasted face down to the inside curve of a piece of concave glass. Flat glass was not so suitable.
The paper backing of the photograph was then carefully removed with sandpaper until only the emulsion was left adhering to the back of the glass. The photograph was then rendered transparent with a slow-drying oil or wax, and the image was ready for the first application of colour.
The intricate detail of the photograph, such as jewellery, lips, and eyes, was then coloured with a fine brush. When this was finished a second, matching curved glass was placed behind the first with spacers to keep it close to, but not touching, the photograph which had just been coloured. The two glasses were then bound together at the edge.
The broad areas of colour were then applied to the back of the second glass, no detail being required as this was on the photograph itself which was now safely sandwiched between the two pieces of glass. Portions of the broad areas of colour could be removed and reapplied until the right effect was achieved, and when the artist was satisfied white card could be attached to the back of the second glass and the whole assembly mounted in a frame.
The process was popular from around 1888 to 1915. 1000′s of examples were produced but only a few survive.
The example below is only in average condition but shows the wonderful clarity of image which this process gives.