of
almost every possible tint ; it may thus become pale-yellow,
deep-yellow, light bottle-green, yellowish-green, blackish-green, blue,
red, brown, and black. Yellowish tints are the most common in "
off-coloured stones : " next to yellow, greenish Diamonds are most
numerous. Blue and red are very rare, and are highly valued as fancy
stones. When the Diamond is between brown and black its transparency
disappears, or is seen only at the angles.
Perfectly colourless Diamonds come from the mines of India, Brazil, the Cape, Borneo, and Australia. Perhaps about one-fourth
of the crystals which come into the market are colourless ; one-fourth
of " pure water," with a flaw or spot of colour ; and the remainder
coloured.
The
coloured Diamonds exhibit their lustre and clearness best when they are
cut, especially the yellow ones, which by candle-light, are very
brilliant
Barbot
is said to have succeeded, by means of chemical agents and a high
temperature, in removing the colouring matter from the rough Diamond ;
but it seems scarcely possible that this can be accurate, though M.
Barbot on the title-page of one of his works styled himself " Inventeur
du Procédé de Décoloration du Diamant brut." Curiously enough, De Boot
asserted 280 years ago, that his Imperial patron, Rudolf II., possessed
a secret which enabled him to clear any Diamond of its flaws and colour.
Various
devices have been resorted to by unprincipled dealers for deceiving the
purchaser in respect to the colour of Diamonds. Thus, the yellow tint
of many off-coloured Cape stones, has been corrected by painting them
with a pale blue solution, or washing them with dilute violet ink. The effect is only temporary, and the trick is of course easily detected by placing the Diamond in spirit.
