The manufacture of gold jewelry produces some floor waste that contains precious metals and its treatment is very important to improve the operating cost of the manufacturing process. This floor waste is basically sweep material, which constitutes the whole of the sweepings from the floors of the workshops in the manufactory, which should in a well-regulated place be swept and collected the same day, and the refuse preserved and carefully sorted every morning with the view of gathering up the small particles of gold visible to the naked eye, which have been dropped during the work of the day. After this has been done, and the gold removed, the waste material must be burnt, and as much of the organic matter destroyed as possible.
The basic process requires the employment of a large mortar, which preserves the material for the refiner. This latter plan may be dispensed with, if found inconvenient in the working department of the establishment; the whole refuse should then be sent periodically homogenized and pulverized, where a large quantity of sweep can be reduced to powder in a very short time. It should of course be previously well burnt, to facilitate the action of crushing system upon the material. The old melting-pots of every, and the burnt cinders and ashes from the furnace and muffles, should also be collected with the sweep; in fact, everything at all worth preserving should be taken care of and sold to the refiner; for it is the attention given these matters in the course of production that constitutes the greatest amount of success in the manufacture of gold jewelry.
The waste material has variable physical properties and change in different workshops. It is important to mention that the specific gravities of the various metals and their alloys has an impact on the material quality and some places are used determine this parameter. Perhaps the more correct method would be to use a hydrostatic balance. This consists of an ordinary balance, of which the pans are suspended by strings of unequal length. The shorter pan has a hook attached to its under side, to which the substance should be suspended by a hair or filament of silk. In ascertaining the specific gravity of any material by these means, it is necessary to find out first its weight, when weighed in air, and secondly to learn how much that weight is reduced by weighing in water. The second weight thus obtained is deducted from the first, and then the specific gravity required is at once obtained by dividing the first weight, or weight in air, by this difference. To conduct this operation with nicety requires great care, and a very delicate balance must be employed in the test, in order to arrive at strictly accurate results.
If the shop floors are well covered with sheet iron, the joints soldered together, and the edges turned up round the ends and sides of the various workshops, it will prevent any of the gold from finding its way into the empty spaces of the flooring, and thus effect a great saving. Sheet zinc may be employed instead of the iron if preferred, but it is more liable to wear through. To prevent this it should be covered with perforated iron gratings; the latter also help to prevent anything from being carried out of the shops which is likely to adhere to the bottoms of the boots of the workpeople, by rubbing it off and collecting it in the holes of the gratings, thus rendering its recovery certain.