February 15, 1894] 



NATURE 



J/ D 



fully good effect. Its great tenacity seems to have been fully 

 recognised, for gold is found in very thin sheets, and laid on a 

 yellow ground, exactly as is done at the present day. 



These pigments are then simply natural minerals, no doubt 

 carefully selected, and sometimes ground and washed previous 

 to being used ; but the blue colour which is so largely used by 

 the Egyptians is an artificial pigment, and consequently has far 

 more interest attached to it than those already mentioned. It 

 is a body requiring considerable care and experience to make, 

 and thus its manufacture enables us to some extent to judge of 

 the knowledge and ability which its producers had of carrying 

 on a chemical manufacture. No doubt the splendid blue of the 

 mineral chessylite was first used, but certainly in the twelfth 

 dynasty — that is, about 2500 B.C. — 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 quantities of each were taken, this 

 necessitating the carefully measuring or weighing of each 

 constituent. An early application of the fundamental 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 pro- 

 duct would be black ; if the alkali was too little in amount, a 

 non-coherent .^^and resulted ; if too much, a hard, stony mass 

 is formed, quite unsuitable for a pigment. The difiiculties, 

 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 experience 

 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 consider- 

 able 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 hsematite powder, 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 arisen from imperfect 

 mixing, or from some parts of the furnace being hotter than ! 

 others. It hardly appears to be intentional, possibly some of 

 the dark, purplish-coloured frits were produced by accident ; 

 large pieces of it have as yet, I believe, not been found. By [ 

 means of coaiparatively small alterations these frits could be 

 obtained of a green colour. One way was by introducing iron. 

 If, for instance, the silica used was a reddish coloured sand, 

 it gave a greenish tinge to the frit ; and frit made with some of 

 the ordinary yellowish desert sand was found to give a frit 

 undistinguishable from the most common of the old Egyptian ; 

 frits. Again, a rather strong green colour is obtained by stop- I 

 ping the heating process at an early stage, this green frit simply 

 on heating lor a longer time becoming blue. Another way in 

 which even the strong-coloured blue frits have been converted 

 into apparently green pigments is by their being coated over 

 with a transparent but yellowish coloured varnish which has to 



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



.SiHca 



Soda 



Copper oxide 



Lime 



Iron oxide, alumina, &c. 



NO. 1268, VOL. 49] 



8865 



o-8i 

 2'og 

 7-88 

 o'57 



a remarkable extent retained its transparency, but no doubt 

 become with age more yellow, and although strongly green 

 now, may very likely originally have been nearly colourless, 

 and consequently the frit was then seen in its original blue 

 colour. Even as early as the twelfth dynasty the green frits 

 used were dull in colour, and if by chance a brighter green 

 was required, then they used the mineral malachite. No doubt 

 by far the most brilliant blue used at any time was selected and 

 powdered chessylite, and even down to the twenty-first dynasty 

 they seem to have made use generally of somewhat brilliant 

 coloured frits ; but after that time more subdued colours 

 appear to have been used, and even the scarabs were made of 

 a much duller colour than formerly. All these blue frits form 

 a perfectly unfadeable and unchangeable pigment. Neither 

 the sun nor acids are able to destroy or alter their colour. 



The only other pigment to which I can refer this evening is 

 the pink colour, which, in different shades, was much used. 

 This is again an artificial pigment, and belongs to an entirely 

 different class from any of the foregoing ones, for it is one of 

 vegetable origin. On simply heating it, fumes are given off 

 and the colour is destroyed, but a large white residue remains ; 

 this is sulphate of lime. It may here be stated that the white 

 pigments used sometimes were carbonate of lime, but more 

 generally sulphate of lime in form of gypsum, alabaster, &c. 

 This substance is often very white in colour, is very slightly 

 soluble in water, and has a singular smoothness of texture, 

 which makes it work well under the brush ; and in addition to 

 I these qualities, it is a neutral and very stable compound, so is 

 well fitted for the purpose to which it was applied. It was 

 easily obtained, being found native in many parts of Egypt. It 

 is also interesting to note that there is an efflorescence consist- 

 ing of this substance which frequently occurs in Egypt, and is 

 of a remarkably pure white colour ; probably this was used as a 

 superior white pigment. It was easy to prove then that the pink 

 colour was gypsum stained with organic colouring matter, and 

 to try and imitate the colour appeared to be the most likely way of 

 identifying it. Naturally, madder, which it is known has from 

 the earliest times been used as a dye, was the vegetable colour- 

 ing substance first tried, and it answered perfectly, giving 

 under very simple treatment the exact shade of colour to the 

 sulphate of lime which the Egyptian pigment had. Essentially 

 the same colouring matter may have been obtained from another 

 source, viz. Munjeet. In the case of madder it is interesting to 

 note that the colour is not manifest in the plant — the Rubia 

 tinctoriim — for it is obtained from the root, and is even not 

 ready formed there. In the root it exists as a glucoside, and this 

 has to be decomposed before the colour becomes manifest. In 

 this root there exist several colouring matters, which are known 

 as madder-red, madder-purple, madder-orange and madder 

 yellow. On breaking up the roots and steeping them in water 

 for some length of time, the colours come out, some sooner than 

 others, so that the tints vary. Again, changes ofcolour are easily 

 obtained by the addition of very small quantities of iron, lime, 

 alumina, &c., so that in these different ways a considerable 

 range of colours could be obtained, but a delicate pink colour 

 was the one probably generally made. This colour is easily 

 obtained by simply stirring up sulphate of lime in a tolerably 

 strong solution of madder, and adding a little lime, taking 

 care to keep the colouring matter in excess ; the colouring 

 matter adheres firmly to the lime salt, and this settles on to 

 the bottom of the vessel; the liquid is then poured off and 

 the solid matter, if necessary, dried, or mixed — probably with 

 a little gum, and used at once without other preparation. That 

 the colouring matter was really madder could also be tested 

 by another method, viz. by means of spectrum analysis. Both 

 the madder-red (alazarin) and the madder-purple (purpurin) 

 give, when the light which they transmit is analysed by the 

 prism, very characteristic absorption bands ; the purpurin 

 bands are the ones most easily seen, consequently it became 

 a point of considerable interest to ascertain whether from a 

 specimen of this pigment, some thousands of years old, these 

 absorption bands could be obtained. A small sample of this 

 pink pigment was taken from a cartonage which was exhibited, 

 and by treating it with a solution of alum, the colour was thus 

 transferred to the liquid, and by throwing the absorption 

 spectrum which it gave on the screen, and comparing it with 

 the spectrum from a madder solution, it was clearly seen to be 

 identical. 



Many specimens in imitation of different coloured frits, and 

 a large copy of a cartonage coloured with pigments prepared by 

 the lecturer, were exhibited. 



