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VOL. LI.] PHILOSOPHICAL TRANSACTIONS. 325 



was found that the colours had penetrated deep into the marbles ; and that 

 many works of his coloured marbles were seen at Oxford and London. But Mr. 

 Bird's way of doing it is not mentioned. 



In the Philos. Trans. N° 268, is a paper, intltled, " The Way of Colouring 

 Marble." The anonymous author gives an account of the colours, &c. he used. 

 It is observable that they are only vegetable colours. His red, he says, he ex- 

 tracted again from the marble, without hurting the polish, within 26 hours, 

 with oil of tartar per deliquium ; and his brown was quite discharged by aquafortis 

 within one quarter of an hour, and the polish of the marble quite destroyed. 



Mr. da Costa now proceeds to give an account of the experiments he made. 



He could not well suggest any more, as the method of colouring the marble, 



the materials of the colours, &c. are kept secret by the artist, Mr. Chambers. 



A piece of marble with the several colours used, on it, like a painter's pallet, 



being greatly saturated with aquafortis, at different times, for 24 hours, though 



the polish of the marble was quite effaced, yet there was not the least discharge 



of any of the colours, nor were they any-wise dulled, &c. — N° 6. A deep 



crimson-red colour, being left 20 hours in a strong lye of common soft 



green soap, suffered no change ; and boiled in the same lye half an hour, also 



suffered no change. The marble finely powdered, and aquafortis effused over it, 



the marble particles were nigh destroyed ; but several red particles (no doubt the 



colour) remained. The marble, by common calcination, i. e. in a common 



coal fire, for half an hour, is entirely discharged of its colour. We made the 



experiments on four other reds, and the result was much the same as abovesaid ; 



so that this is a standard for his reds. 



N'^ 5. A deep sea-green, being left 20 hours in a strong lye of common soft 

 green soap, suffered no change; but boiled in the same lye it quite discharged 

 its green colour : however, it yet remained slightly tinctured yellowish. By 

 common calcination the colour was quite discharged. Some other greens were 

 tried, and answered much the same. — N*^ JO, 15, and 16, brownish or terres- 

 trial yellowish colours, near to a clay colour, boiled in a strong lye of common 

 soft green soap, they suffered no change. By common calcination the colours 

 were discharged, but retained a greyish cast. These colours, covered for 48 

 hours with a layer of the said common soap, suffered no sensible change. — N° 

 19, A bright yellow, boiled in a strong lye of common green soft soap, suffered 

 no change ; and covered with a layer of the same soap for 48 hours, the colour 

 is dulled. By common calcination the colours are discharged, but retain a grey- 

 ish cast. Several other different shades of yellow answered much the same. 

 Mr. Chambers has not as yet stained any marble of a blue colour. 



By the above experiments we may conclude, that these colours are good, 

 penetrate the marble freely without injuring it, remain uninjured by menstrua. 



