You will need
- - tin 1-2 l;
- - nichrome wire;
- - sheet asbestos;
- - clay;
- - refractory clay;
- - cardboard;
- - long tongs;
- - lead.
Wrap a jar of nichrome wire. Dilute clay with asbestos crumb in the ratio of 1:5 and the mix, coat the coil. Dry the muffle within 3-5 days. Lay on the bottom of the jar asbestos sheets.
Stir the clay, fireclay and asbestos crumbs in equal proportions. Vilaite the ready-made cardboard form the working chamber (Cup) and the muffle furnace door thickness of 1 cm, Wait for the drying chamber and separate from it the form. Install in a jar crucible and calcined for several hours before first use at a temperature of 1000 °C.
Connect the oven to the mains AC 220 V. After heating, the furnace is put into the working chamber forceps technical silver and lead. Depending on the amount of impurities in the silver, you need to use from 0.5 to 8 grams of lead. Insufficient lead will lead to low quality of separation of impurities, at the same time too large amounts of lead will increase and the consumption of silver.
Lead and its oxide – lead litharge the melting absorbed into the walls of the crucible. A feature of the litharge is that it wets the crucible and with it wall drawn other metals and their oxides, in particular copper and Nickel. As the absorption of lead in the walls of the chamber, the molten mass will become more shiny. When a strong luster or so-called "silver flash", disconnect the oven from the mains.
Remove the silver "ball" from the crucible and clean it from toxins.
Do not heat the furnace too much work at furnace temperatures not exceeding 1000 °C to reduce the evaporation of silver. At the same time for quality cleaning silver from impurities maintain the furnace temperature of not less than 960 °C (the melting point of silver).
Use cupellation in the absence of the impurities gold and platinum.