1893.] on Ancient Egyptian Pigments. 69 



— these artificial blues were used. They are all an imperfect glass, 

 a frit, made by heating together silica, lime, alkali, and copper ore.* 

 The number of failures which may have occurred, and how much 

 material may have been spoilt, cannot be known, but all the blue frit 

 which I have examined — and it is a considerable amount, some being 

 raw material, lumps as they came from the furnace, and the rest 

 ground pigment — all has been, though differing in grain and quality, 

 well and perfectly made. Now this implies that the materials have 

 been carefully selected, prepared, and mixed, and that definite quan- 

 tities of each were taken, this necessitating the carefully measuring or 

 weighing of each constituent. An early application of the fun- 

 damental law of chemistry, combination in definite proportion. The 

 amount of copper ore added determined the colour ; with 2 to 5 per 

 cent, they obtained a light and delicate blue ; with 25 to 30 per cent. 

 a dark and rather purple blue ; with still more the product would be 

 black; if the alkali was too little in amount, a non-coherent saud 

 resulted ; if too much, a hard, stony mass is formed, quite unsuitable 

 for a pigment. The difficulties, however, did not by any means 

 end with the mixture of the materials. For the next process, 

 the heating, is a delicate operation. Unfortunately up to the present 

 time the exact form of furnace in which this operation was carried 

 on is not known. The furnaces were probably, especially after use, 

 very fragile structures, and have passed away. Considerable ex- 

 perience in imitating these frits even when using modern furnaces has 

 taught me that the operation is really a very delicate one ; the heat 

 has to be carefully regulated and continued for a considerable length 

 of time, a time varying with the nature of the frit being prepared ; 

 and, further, in the rough furnaces used it must have been specially 

 difficult to have prevented unburnt gases from coming in contact with 

 the material ; but if they did a blackening of the frit must have 

 taken place. However, all these difficulties were avoided, and a frit 

 was made which exactly answered all the necessary requirements. 

 It had, for instance, the right degree of cohesion, for many of the 

 large pieces which have been found have, like the haematite, a smooth, 

 curved striated surface, and on rubbing in a curved vessel with 

 water, easily grind to powder. The powder is naturally much less 

 adhesive than the haematite pow r der, but on adding a little medium, 

 it could at once be used, without other preparation, as a paint. 

 Some of the pieces vary in colour in different parts. This may have 



* A sample of the pale-blue frit gave, on analysis, the following results : — 



Silica .. .. .. .. .. 88-65 



Soda .. .. .. .. .. .. 0-81 



Copper oxide .. .. .. .. .. 2*09 



Lime.. .. .. .. .. .. 7*88 



Iron oxide, alumina, &c . . . . . . 0*57 



10000 



