Polishing of precious metals (jewellery polishing)

Currently for cleaning of precious metal products after melting and soldering, as well as for final polishing, mechanical and electrochemical polishing is applied. Application of mechanical methods for jewellery processing is connected with hard, laborious manual work. For electrochemical treatment a highly concentrated solution is required. Table 1 presents chemical compositions of electrolytes for electrochemical polishing.

Table 1. Components of electrolytes for electrochemical jewellery polishing of gold alloys

Components Component's mass fraction, g/l
  ЗлСрПдМ Grade ЗлСрМ Grade ЗлСрМ Grade ЗлМНЦ Grade ЗлСрМ Grade
Ammonium thiocyanic 150 – 200 50 – 70 10 – 20 20 – 70
Lactic acid 6,0 – 8,5 6,0 – 8,5
Sulphuric acid 30 – 50 30 – 70 30 – 50 30 – 50 30 – 70
Sodium chloride 10 – 20
Thiourea 60 – 90 60 – 90 60 – 90 60 – 90 60 – 90

Electrolyte-plasma technology allows to make fast high-quality polishing of products. The use of manual labour is minimized, and the concentration of electrolyte substances is significantly less than that by electrochemical processing. After electrolytic-plasma processing a product acquires stable brightness, scratches are removed. There are electrolytes designed not only for gold, but also for other precious metals. For recovery of a metal from electrolytes electrochemical or chemical methods are employed.  

The particular interest to electrolyte-plasma jewellery polishing of precious metals is conditioned by the fact, that, after taking off treated surfaces, precious metals being in the electrolyte can be easily recovered by settling or with the help of chemical catalysts.