State The Best Smalt In Lumps Appears Black Yields A Blue Powder On

grinding, becomes paler on further grinding, and may be almost

decolourised by continued and excessive grinding. Smalt, it has been

stated, is merely a blue glass; and when a piece of blue glass, or a

blue crystal of sulphate of copper, is reduced to the fineness of flour,

the blue is lost. In vitrified and crystallised compounds, colour

depends on cohesion: sufficiently separate the particles, and the colour

more or less disappears. Not only, moreover, does grinding effect an

optical change in vitreous pigments, but it imposes further alteration.

That colour which was safe when locked up in a mass, crushed to minute

atoms is no longer so: imbedded in glass or enamel it will endure for

ages, but ground to impalpable powder becomes as liable to influence as

though it had never been subjected to heat at all. To sum up, vitreous

pigments are durable in a coarse or compact form, but are not more

stable than others when reduced to extreme division. As far as regards

Splendid Viridian A Green Nothing But Fire Will Change And No Subdued Blue These Are Often Beautifully Opposed In Nature Being facebooktwittergoogle_plusredditpinterestlinkedinmail