Early attempts made to obtain the exquisite blue tint of the true sapphire were frustrated by an unexpected difficulty. The colouring matter, cobalt oxide, was not diffused evenly through the drop, but was huddled together in splotches, and it was found necessary to add a considerable amount of magnesia as a flux before a uniform distribution of colour could be secured. It was then discovered that, despite the colour, the stones had the physical characters, not of sapphire, but of the species closely allied to it, namely, spinel, aluminate of magnesium. By an unsurpassable effort of nomenclature these blue stones were given the extraordinary name of ‘Hope sapphire,’ from fanciful analogy with the famous blue diamond which was once the pride of the Hope collection. A blue spinel is occasionally found in nature, but the actual tint is somewhat different. These manufactured stones have the disadvantage of turning purple in artificial light. By substituting lime for magnesia as a flux, Paris, a pupil of Verneuil’s, produced blue stones which were not affected to the same extent. The difficulty was at length overcome at the close of 1909, when Verneuil, by employing as tinctorial agents 0·5 per cent. of titanium oxide and 1·5 per cent. of magnetic iron oxide, succeeded in producing blue corundum; it, however, had not quite the tint of sapphire. Stones subsequently manufactured, which were better in colour, contained about 0·12 per cent. of titanium oxide, but no iron at all. By the addition to the alumina of a little nickel oxide and vanadium oxide respectively, yellow and yellowish green corundums have been obtained. The latter have in artificial light a distinctly reddish hue, and have therefore been termed ‘scientific alexandrite’; of course, quite incorrectly, since the true alexandrite is a variety of chrysoberyl, aluminate of beryllium, a very different substance. If no colouring matter at all be added and the alum be free from potash, colourless stones or white sapphires are formed, which pass under the name ‘scientific brilliant.’ It is scarcely necessary to remark that they are quite distinct from the true brilliant, diamond. The high prices commanded by emeralds, and the comparative success that attended the reconstruction of ruby from fragments of natural stones, suggested that equal success might follow from a similar process with powdered beryl, chromic oxide being used as the colouring agent. The resulting stones are, indeed, a fair imitation, being even provided with flaws, but they are a beryl glass with lower specific gravity and refractivity than the true beryl, and are wrongly termed ‘scientific emerald.’ Moreover, recently most of the stones so named on the market are merely green paste. It is unfortunate that the real success which has been achieved in the manufacture of ruby and sapphire should be obscured by the ill-founded claims tacitly asserted in other cases.