Encyclopædia Britannica 1797/XVII

Encyclopædia Britannica; or, a Dictionary of Arts, Sciences, and Miscellaneous Literature, Constructed on a Plan, by which the different Sciences and Arts Are digested into the Form of Distinct Treatises or Systems, comprehending The History, Theory, and Practice, of each, according to the Latest Discoveries and Improvements, and full Explanations given of the various detached Parts of Knowledge… The third Edition… XVII, Edinburgh [Andrew Bell – Colin Macfarquhar] 1797.

pp. 541–542

Smalt

SMALT, a kind of glass of a dark blue colour, which when levigated appears of a most beautiful colour; and if it could be made sufficiently fine, would be an excellent succedaneum for ultramarine, as not only resisting all kinds of weather, but even the most violent fires. It is prepared by melting one part of calcined cobalt with two of flint powder, and one of pot-ash. At the bottoms of the crucibles in which the smalt is manufactured we generally find a regulus of a whitish colour inclining to red, and extremely brittle. This is melted afresh, and when cold separates into two parts; that at the bottom is the cobaltic regulus, which is employed to make more of the smalt; the other is bismuth.