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ferent coloured pieces; and compositions which have beenspoilt, in trying to tinge them of other colours, answer aswell for this purpose as any.

The common black glass, of which beads are made fornecklaces, &c. is coloured, as I am informed, with man-ganese only; hence when powdered it looks of a dirtypurple colour. The manganese perhaps increases the fu-sibility of the glass, for an ingenious friend observes, thatin making impressions in different kinds of glass, he hasfound this black fort to be by far the most fusible of any.That there is a strong action between the manganese andthe glass may be presumed from the great effervescencewhich happens on melting them together. One part ofmanganese is sufficient to give a black colour to neartwenty of glass.

The enamellers require a black more perfect than thatwhich manganese alone can produce, and employ, as Iam informed by an experienced artist, a mixture of man-ganese, zaffre, and scales of iron. These ingredients maybe mixed together in equal quantities, and one part of themixture added to fifteen or twenty of the basis of enamels;which basis is prepared by calcining a mixture of aboutequal parts of lead and tin, and melting this calx with.equal its quantity of fritt or powdered glass.

VII.