Alternativa: Crucible for (precious metals) refining

Ciao Ivana, non credo sia quello il significato che dovresti considerare per coppella, ma questo
2 forno in cui avviene la coppellazione (De Mauro)

http://www.carbolite.co.uk/products.asp?id=18&doc=18
http://www.researchportal.be/en/project/optimisation-of-refr...

Operazione chimica che consente la estrazione dell'argento dal piombo argentifero. Scaldando in una coppella il piombo al calore rosso, esso ed altre impurita', quali l'arsenico, il bismuto e l'antimonio, si ossidano, mentre l'argento rimane allo stato metallico. Gli ossidi vengono di sciolti nel litargirio fuso, e l'argento puo' essere facilmente separato assieme agli altri metalli nobili eventualmente present�, quali l'oro e il platino, che non si ossidano all'aria neppure alle alte temperature. La coppellazione e' usata anche per l'affinamento dell'oro e per determinare il suo contenuto nelle leghe.
http://www.e-vocabolario.com/stamp_parola.php?&id=1651&tit=C...

Cupellation is a process used to separate noble metals such as gold or silver from base metals such as lead. It is often used to assay gold in order to test its purity. Sometimes cupellation is called "fire assaying." It was formerly the usual process for extracting silver from lead.

In this process, an alloy consisting of both noble and base metals is placed in a crucible. This mixture is then melted and allowed to freeze. When solidified, a button consisting of precious metals and lead can be removed from the slag of metal oxides and other materials. When assaying ores this slag layer can be quite massive, but when assaying karat gold, it is virtually non-existent. After cooling, the metals are placed in a special pot made of bone ash or clay called a cupel. Under high heat, lead turns to litharge, a lead oxide, which is absorbed by the cupel or lost to the atmosphere. At the end of the cupellation process, a button of pure gold and silver remains in the bottom of the cupel. The button is then placed in nitric acid to dissolve the silver, and the remaining pure (24k) gold weighed to determine the gold content present in the original starting material.
http://en.wikipedia.org/wiki/Cuppelation

http://en.wikipedia.org/wiki/Crucible