Among colors of Diamonds, blue is the rarest. The largest and most valuable colored Diamond known is the Hope Blue, weighing 44½ carats. This is valued at about one hundred thousand dollars. It has a brilliant deep blue color and is without a flaw. A deep blue Diamond weighing 67-2/16 carats was long worn in the French crown, but it was stolen in 1792 and has never been recovered. Red Diamonds vary in hue from ruby red to rose, the latter being the most common. No large red Diamonds are known, the largest being one of 32 carats in Vienna. Another famous one is that in the Russian treasury, for which Paul I paid one hundred thousand roubles. It is of a ruby color. The finest green Diamond known is the “Dresden Green” preserved in the Green Vaults of Saxony. It was purchased by August the Strong in 1743 for sixty thousand dollars. It is apple green in color and weighs 40 carats. Diamonds of yellow color are comparatively common, many of the Cape Diamonds being lowered in value by possessing a yellow tinge. It is said that this injurious yellow tinge can be overcome by dipping the stone several times in a solution of potassium permanganate, the violet color of the latter neutralizing the yellow of the Diamond. The yellow tinge usually also disappears in artificial light. Of large Diamonds possessing a yellow color the Florentine and the Tiffany are the best known. The color of colored Diamonds is generally permanent, but that of some is said to fade on exposure to light. It can also be destroyed or changed by heat. The luster of the Diamond is a peculiar one, and such as is possessed by few other minerals. In reference to its occurrence in the Diamond it is known as the adamantine luster. It combines the peculiarity of an oily luster with that of glass and that of a metal. It is doubtless due to the high refractive power of the mineral, which causes more than the ordinary number of rays of light to come to the eye. In the impure forms of Diamond the greasy or oily luster becomes more pronounced. Once the eye becomes accustomed to the peculiar luster of Diamond the stone may easily be distinguished by it from glass or minerals with a vitreous luster, such as quartz. Certain other minerals, however, such as cerussite, zircon, and to some extent sphene, exhibit the adamantine luster. In the glass known as strass, used to make imitation Diamonds, the adamantine luster is well imitated.