184 Chemical Aids to Art. 



practice before it can be accomplished with perfect success, 

 and it probably admits of improvement. It has the advantage 

 of great durability ; it is applicable to a great variety of objects 

 and materials, while the silver employed is of the utmost purity 

 and beauty. 



It may interest our readers to know how this process 

 originated. The author of the present paper had occasion 

 to illustrate in a lecture the readiness with which many salts 

 of silver are decomposed by heat. For this purpose some 

 nitrite of silver was placed on the blade of a penknife and 

 heated over the spirit-lamp ; the residue of silver left on the 

 blade was afterwards found to be so firmly attached to the 

 blade that it required to be filed away. This accidental 

 observation led to further experiments, the final result of 

 which was the process we have now described. 



Metals are occasionally inlaid with coloured pigments and 

 with enamels. True enamelling on inferior metals, such as 

 bronze, brass, and copper, is not, however, now often prac- 

 tised, and we have to be content with the inferior substitutes 

 for it which oil colours and different kinds of sealing-wax 

 afford, for of such materials consist the so-called enamelled 

 ornament which we often see on the otherwise excellent 

 mediaeval brass work so abundantly manufactured at the 

 present day. A hard and purely mineral substitute for these 

 oil paints and coloured preparations of shellac has long been a 

 desideratum. The process now to be described, although far 

 from perfect, is capable of affording some admirable artistic 

 effects. The materials employed have been used, for some 

 years by dentists as a white stopping for teeth. Exactly in 

 the same way they may be used as an inlay for almost any 

 material in which grooves, channels, or hollows have been 

 previously cut. This dental preparation goes under the name 

 of <c osteo-plastic " and " os-artificiel." It is made of oxide 

 of zinc, worked into a paste with a strong solution of chloride 

 of zinc ; these two zinc compounds chemically combine to- 

 gether, heat is given out, and in a few minutes a hard, dense, 

 insoluble white mass is formed, which, when properly pre- 

 pared, is almost indestructible. The dental os-artificiel gene- 

 rally contains about 10 per cent, of quartz powder, added to 

 increase the hardness of the composition ; but, in using the 

 oxy chloride of zinc for decorative purposes, this addition is 

 unnecessary, while the admixture of various dry powdered 

 colours, on the other hand, greatly enhances and diversifies 

 the effects producible. The following mineral pigments may 

 be used in the proportion of one part of pigment to nine of oxide 

 of zinc : vermilion, oxide of chromium, cadmium yellow and 

 cobalt blue. The oxide of zinc must be very pure and very 



