Schwanhart of the process of etching on glass by means of hydrofluoric acid, and the rediscovery by J.
In the 17th and 18th centuries the processes of scratching, engraving and etching were brought to great perfection.
A little before his death he had also formed a scheme of writing a Discourse on the Arts of Painting, Sculpture, Etching, &c., but when he died he had made but little progress with it.
Fluorides can be readily detected by their power of etching glass when warmed with sulphuric acid; or by warming them in a glass tube with concentrated sulphuric acid and holding a moistened glass rod in the mouth of the tube, the water apparently gelatinizes owing to the decomposition of the silicon fluoride formed.
Dark coloured micas are strongly pleochroic. Accurate determinations of the optical orientation, as well as the symmetry of the etching figures on the cleavage planes, seem to suggest that the micas, except muscovite, may be anorthic rather than monoclinic in crystallization.