NATURAL PHILOSOPHY. 147 



ous attempts which have, from time to time, been made to introduce 

 a substitute for glass-painting in the decoration of houses, I believe it 

 can be said that a want was generally felt for supplying the growing 

 taste for pictorial decoration ; for glass-painting is an expensive pro- 

 cess, and requires also a considerable time to obtain a perfect result. 

 There, is a process known as lithophany, or transparent china, or 

 biscuit slabs, which are now made, in Germany principally, and some 

 very good specimens can be seen ; but although any kind of subjects, 

 on a small scale, can thus be represented, and with a very good effect, 

 the slabs are heavy and thick, and can never come into use as a sub- 

 stitute for glass-painting. Some few years ago, a new mode, which 

 was then termed ' potichomany,' was introduced, which had for a 

 short time very great success I allude to the mode of pasting colored 

 prints inside a large glass bowl, or jar, and applying a thin layer of 

 plaster of Paris, in a liquid state, so as to fix the paper firmly, and 

 create an opaque back-ground, by giving substance to the whole, when 

 seen from a distance. Some very good specimens of this were 

 obtained, and it afforded for a time an agreeable occupation to many 

 a young lady. Another mode has also been tried, and some very 

 pretty results produced, by applying prints obtained by lithochroniy, 

 or lithographic printing in colors, on a pane of glass, and varnishing 

 them at the back with copal or some such varnish ; these will for some 

 time resist the effects of the weather when placed in a window ; and 

 this is perhaps the nearest approach to glass-painting in point of effect 

 yet achieved, but practically it does not answer, for the varnish will 

 not stand exposure to the weather from outside, and the constant 

 cleaning glass requires renders it liable to be injured, so that the 

 design soon perishes. 



In the mode which is now for the first tune introduced, no such dan- 

 ger or liability need be feared, since the color has been firmly fixed 

 in the substance of the glass by fire, and, being composed of the same 

 elementary materials, has become part of the glass itself, and can only 

 be destroyed by the glass being annihilated by breakage. 



In order that the process may be very distinctly understood, I shall 

 now describe it by reading that part of my specification which relates 

 to the placing the image on the glass, fixing it, and passing it through 

 the fire. 



For this purpose I proceed in the following way : A piece of glass, 

 which may be crown or flatted glass, being selected, as free from defect 

 as possible, is first well cleaned, and held horizontally while a certain 

 liquid is poured on it. This liquid is composed of a saturated solution 

 of bichromate of ammonia in the proportion of five parts, honey and 

 albumen three parts of each, well mixed together, and thinned with 

 from twenty to thirty parts of distilled water, the whole carefully fil- 

 tered before using it. The preparation of the solution, and the mixing 

 up with other ingredients, should be conducted in a room from which 

 light is partially excluded, or under yellow light, the same as in pho- 

 tographic operating rooms, so that the sensitiveness of the solution 

 may not be diminished or destroyed. 



In order to obtain a perfect transfer of the image to be reproduced, 

 the piece of glass coated with the solution, which has been properly 

 dried by means of a gas-stove (this will only occupy a few minutes), is 



