Formerly all argentiferous lead had to be cupelled, and the resulting litharge then reduced to metallic lead.
In 1833 Pattinson invented his process by means of which practically all the silver is concentrated in 13% of the original lead to be cupelled, while the rest becomes market lead.
It holds its own, however, when base bullion contains bismuth in appreciable amounts, as in the Pattinson process bismuth follows the lead to be cupelled, while in the Parkes process it remains with the desilverized lead which goes to market, and lead of commerce should contain little bismuth.
The base bullion is imperfectly Pattinsonized, giving lead rich in silver and bismuth, which is cupelled, and lead low in silver, and especially so in bismuth, which is further desilverized by the Parkes process.
Deep, about 6 tons of lead are cupelled in twenty-four hours.
Before it can be cupelled it has to be freed from most of the zinc, which is accomplished by distilling in a retort made of a mixture similar to that of the plumbago crucible.
In the second, the lead button containing the gold or silver is cupelled and the resulting gold or silver button is weighed.