This video shows the primary refining stage for scrap gold.

Tin, lead, and zinc volatalize or boil off in this process leaving behind an ingot of mostly gold, silver, and copper.

What is Thermocouple Wire?

Platinum thermocouple wire is used as a sensor for measuring temperature, that consists of two dissimilar metals that are joined together at the sensing end. Typically platinum and rhodium. Different thermocouple types (e.g. R, S, B, etc.) use different alloys of platinum and rhodium in the wire.

The resistance to the flow of electricity in metallic materials varies with temperature. This can be used to good effect in platinum resistance detectors. Platinum is particularly stable both electrically and mechanically and is also stable with respect to time, producing a relatively linear change in resistance versus temperature.
Because the output resistance change to temperature is relatively small, it follows that lead lengths and resistances are therefore important features. In general when lead lengths are short, or can be considered as an acceptable additive content, two wire configuration is sufficient.

Thermocouples employing platinum in combination with platinum-rhodium alloys, gold, or palladium have been found to be the most reproducible of all the various types. They are resistant to oxidation in air and, because of their high melting points, can be used up to very high temperatures. The best-known member of this group is Pt10Rh/Pt* (or type S, or 10/0).

Platinum thermocouple wire can be worth as much as $50 per gram