son
who has not had sufficient experience to instinctively estimate and
balance the various influences by which he may be surrounded, it is
quite difficult to grade a stone at sight.
Looking
intently or for a considerable period at some decided color just prior
to looking at a diamond, will influence the judgment. Some effect of
the accidental or complementary color thereby produced, undoubtedly
remains, and becoming mixed with the new impression, produces a
sensation of color which is not true to the last thing brought under
observation. For instance, if one, after working for some time over a
paper of emerÂalds, were suddenly called upon to judge a fine white
diamond, he would probably see a tinge of brown in it. The brown would
not be in the stone; it would be a leftÂover impression, or the ocular
spectra produced by gazing at the green emeralds. In a like manner
amethysts or blue sapphires would prejudice against white stones by
creating an impression of yellow. On the other hand, the blue of a
bluish white stone would be intensified to a purplish or violet tint by
first fixing the eye for a short time upon yellow sapphires or topaz,
or a canary diamond. The off-hand adverse criticism by a buyer, or the
buyer's adviser, of a stone which is really white, often tempts the
dealer to allow his customer to deceive himself and sometimes obliges
him to sell a poorer stone at a higher price than that he would have
preferred to sell.
Color
is often unequally distributed through the stone, or the elements which
cause the sensation of color are so placed that position modifies it.
There are stones which show more color when viewed from the back than
