Royal Institution. 8^7 



be beneficially employed as a substitute for size in white- washing 

 and staining walls. It was demonstrated by several experiments 

 that carbonate of lime, mixed up with a weak solution of water-glass, 

 and applied as a whitewash to surfaces, was not washed off by 

 sponging with water, and that common whitewash, laid on in the 

 usual manner with size, was rendered equally adhesive when washed 

 oyer with water-glass. 



III. The Stereochrome of Fuchs. — The formation of an insoluble 

 cement by means of the water-glass, whenever the carbonic acid of 

 the atmosphere acts on this substance, or whenever it is brought in 

 contact with a lime- salt, has been applied by Fuchs to a most im- 

 portant purpose. The stereochrome is essentially the process of 

 fresco secco* invested with the capability of receiving and perpe- 

 tuating works of the highest artistic character, and which may be 

 executed on a vast scale. Fuchs's method is as follows f: — 



"Clean and washed quartz-sand is mixed with the smallest quan- 

 tity of lime which will enable the plasterer to place it on the wall. 

 The surface is then taken off with an iron scraper, in order to re- 

 move the layer formed in contact with the atmosphere ; the wall 

 being still moist during this operation. The wall is then allowed 

 to dry ; after drying it is just in the state in which it could be rubbed 

 oflf by the finger. The wall has now to be fixed, i. e. moistened with 

 water-glass J. [An important point is not to use too much water- 

 glass in moistening the wall.] This operation is usually performed 

 with a brush. The wall must be left in such a condition as to be 

 capable of receiving colours when afterwards painted on. If, as 

 frequently happens, the wall has been too strongly fixed, the surface 

 has to be removed with pumice and to be fixed again. Being fixed 

 in this manner the wall is suffered to dry. Before the painter 

 begins, he moistens the part on which he purposes to work with 

 distilled water, squirted on by a syringe. He then paints : if he 

 wishes to repaint any part, he moistens again. As soon as the 

 picture is finished, it is syringed over with water-glass. After the 

 wall is dry, the syringing is continued as long as a wet sponge can 

 remove any of the colour. An efflorescence of carbonate of soda 

 sometimes appears on the picture soon after its completion. This 

 may either be removed by syringing with water, or may be left to 

 the action of the atmosphere." Not to dwell on the obvious ad- 

 vantages possessed by the stereochrome over the real fresco, (such 

 as its admitting of being retouched and its dispensing with joinings), 

 it apjjears that damp and atmospheric influences, notoriously de- 

 structive of real fresco, do not injure pictures executed by this process. 



* Vide Eastlake's Materials for a History of Oil Painting, p. 142. 

 t These particulars were obtained by Dr. Hofmann from Mr. Echter. A 

 •tercoohroniic picture by Echter and a sample of the water-glass as pre- 

 pared in Munich were also exhibited by Dr. llofraann. 

 J The composition of the specimen was — 



per cent. 



Silica 2.'J-21 



Soda 8-90 



Potash 2-52 



[The specific gravity of the solution .3'8l.] 



