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The porous marbles, which admit water to fink intothem, 1 have stained of a full black colour with commonink; either by applying on the warm marble an inkalready made, or by the alternate application of astringentliquors and solutions of iron. With the more compactmarbles, this did not succeed, though they were heated sofar as to make the liquors boil upon them : in some partsthe colouring matter scarcely penetrated at all; and whereit did sink a little into the stone, it was so dilute as toappear only purplish. The spirituous tinctures, describedin page 388, made without the mastich, seemed to pene-trate better than the watery infusions.

On marbles which would not receive the inky matter,1 tried the alternate application of solutions of lead andof sulphureous solutions, applying sometimes the one first,and sometimes the other; but could not find that theyproduced in the stone any degree of the black or darkcolour which they do on paper. By solution of copper,managed as at the end of the following article, and by asolution of the metallic part of cobalt in aqua regia, em-ployed in the same manner, the most compact pieces werestained black; though this process requires too great aheat to be practised on marble without danger of injuringthe stone. The colour which solutions of gold commu-nicate to marble, in its deep shades obtained by repeatedapplications of the solution, approaches very near to black -

IV. Agate, &c.

Several of the hard stones, which strike fire withsteel, receive a dark stain inclining to black from solutionof silver. Mr. du Fay relates, in the French Memoirsfor 1728, that to chalcedony, this solution gave a reddishbrown colour; to oriental agate, a blacker stain; to anagate spotted yellow, a purple; to the jade stone, a pale

L 11 2 brown;