#921. To produce a picture instantly, in a variety of colours

- By Formula pot


  • Refer procedure


Paint any picture on paper in the usual way, only instead of colours, use the following substitutes: for green, use a solution of nitro-muriate of cobalt, for blue, a solution of sulphate of iron—for yellow, a solution of nitrate of bismuth—and for a brown, a solution of sulphate of copper. Any of these solutions may be more or less diluted, as the respective parts of the picture are to be light or dark, but none of them must be strong enough to colour the paper. This pictture is invisible: but when it is required to appear, the paper may be tacked up on the wall, and having a glass of the transparent solution of prussiate of potass (which by sight cannot be distinguished from clear water) dashed suddenly upon it, the picture will instantly appear in its full colours. A similar effect may be produced, by drawing the picture with infusion of galls, and sub-carbonate of potass; this is revived by a solution of sulphate of iron, and appears in a yellow and a brown colour.