During the manufacturing process of gold jewelry articles some material is considered as waste and receives a special treatment in order to recover gold and other precious metals. For example, the sediment which accumulates in the scratch brush and polishing-boxes, lappers cotton waste, and all other waste of a similar description, should be carefully collected and thoroughly burnt in a closed iron pan, or other suitable vessel. This process will considerably reduce the bulk of it, and also destroy any organic matter that may be present. The burning must be cautiously effected, to prevent the light particles of gold from going with the draught up the chimney; and for this same reason, it is advisable to employ for such purposes a strong iron pan with a lid to it.
It important to indicate that when the burning has been carried far enough which, with a steady fire, will occupy a whole night for each pan full of waste and refuse, and the operation is finally completed, the remaining ash must be put through a fine sieve; the refuse which remains in the sieve should be pounded, and again sifted, when the waste is what is called good, and is then ready for the refiner test. If it is desired to collect the gold from the above and a good plan should be resorted to recover the gold. The mixture of waste material and fluxes is variable and as an indication it may content 53% of waste material, 27% of potassium carbonate, 12% of sodium chloride and the difference is sal-enixon. The fluxes must be reduced to powder and well mixed with the waste.
The mixture to be treated is not as heavy as the gold dust and great proportion of chemical compounds is required to assure a good dissolution of gold and form a button. After being carefully prepared, the mixture is placed into a crucible and at the end of the melting process when perfectly fused, a very few crystals of potassium nitrate are added as a quicker fusion is obtained by imparting moisture or liquidness to the preparation. The action of the potassium nitrate on the mixture must at first be closely watched, and if it is at all likely to overflow, a small quantity of dried common salt should at once be thrown in, as it has a great tendency to force the flux downwards. If sufficient potassium nitrate has been added to the fused mass it will remove from the gold whatever iron, steel, zinc, and even brass and copper, may be present; leaving the gold in a button at the bottom of the crucible, which should subsequently be broken at the base for its recovery, after standing a sufficient time for cooling.
The presence of excessive quantities of silica, mercury chloride, brown potash, and sal-enixon are all useful fluxes, having a tendency to destroy the impurities in precipitates of this kind. It is not a good idea to collect the gold from the waste material without an appropriate technical knowledge of the process. It is unprofitable to the manufacturing goldsmith, considering the cost of materials, heating, and time in effecting it. When the jeweler has not experience, the safest and most economical plan is to send the material to a special place to recover the gold. It is important to determine the gold content of the material so that the full value is then obtained.