Engraving is a simple process in itself, and diversity of effect can be produced by skilful manipulation. An interesting variety in the effect of a single ornament may be produced by the combination of coloured gold of various tints. This colouring is a process requiring skill and experience in the manipulation of the materials according to the quality of the gold and the amount of silver alloy in it. The objects to be coloured are dipped in a boiling mixture of salt, alum and saltpetre. Of general colouring it may be said that the object aimed at is to enhance the appearance of the gold by removing the particles of alloy on the surface, and thus allowing the pure gold only to remain visible to the eye. The process has, however, gone much out of fashion. It is apt to rot the solder, and repairs to gold work can be better finished by electro-gilding. The application of machinery to the economical production of certain classes of jewelry, not necessarily imitations, but as much "real gold" work, to use a trade phrase, as the best hand-made, has been on the increase for many years. Nearly every kind of gold chain now made is manufactured by machinery, and nothing like the beauty of design or perfection of workmanship could be obtained by hand at, probably, any cost. The question therefore in relation to chains is not the mode of manufacture, but the quality of the metal. Eighteen carat gold is of course preferred by those who wear chains, but this is only gold in the proportion of 18 to 24, pure gold being represented by 24. The gold coin of the realm is 22 carat; that is, it contains one-twelfth of alloy to harden it to stand wear and tear. Thus 18 carat gold has one-fourth of alloy, and so on with lower qualities down to 12, which is in reality only gold by courtesy. It must be remembered that the alloys are made by weight, and as gold is nearly twice as heavy as the metal it is mixed with, it only forms a third of the bulk of a 12 carat mixture.