Gold. This beautiful metal always has been the one most used for jewellery, partly because of its rich appearance, partly because it is very easily worked, and also because it does not tarnish.
It is not often used pure. The reason generally given for alloying it is that it is too soft for use in its natural state ; but the most exquisite ornaments ever made, in two widely differing styles Greek and Etruscan work, and the enamel jewellery of the Renaissance are both made of gold which is of a very high standard, about twenty-two carats as a rule. The quality of gold is described by the expression, “so many carats,” fine or pure gold being taken as twenty- four. Thus eighteen carat gold means that there are six parts of alloy to eighteen of gold ; twenty-two carat means that there are only two of alloy, and so on. Besides the alloys made for convenience in wear and working, gold is also alloyed with various metals in order to alter the colour.
Fine gold is an exquisite rich, but rather pale, yellow ; alloyed with silver in a small proportion (four to ten pennyweights to the ounce) it has a greenish hue ; copper (five to ten pennyweights to the ounce) gives a reddish tint ; the addition of a third of its weight in iron forms “blue gold” ; and when alloyed with silver in the proportion of half and half, ” white gold ” is the result.
The process known as colouring gold consists in the removal of the alloy from the surface, leaving only a thin film of fine gold exposed ; this soon wears away and leaves the base quality of metal exposed, giving a very tawdry appearance. Things thus dealt with are not earlier than the first quarter of the nineteenth century. Gilding, however, was known from very early times and often has worn splendidly, silver-gilt pieces of the sixteenth century often retaining a considerable share of the original coacing.
The usual test for gold to distinguish it from base metals is by scraping the gold object in question onto a special stone and dripping different acid concentrates to see different colouration changes in order to determine the grade of gold in question. Most countries require that objects made with gold that is equal to or greater than 9 karats be hall marked to ensure that an is exact standard of gold used. The hall marks may be in the form of x/24 carats, karats, ct, kt, or k. Generally, French speaking countries (France, Switzerland and parts of Canada) use carat or ct. Hall marks showing the purity of gold used may also be in decimal form, such as .9999 (such as for Canadian gold maple leaf coins) or .75 being the equivalent of 18 kt. gold.
