text: The Pattinson process was patented by its inventor, Hugh Lee Pattinson, in 1833 who described it as "An improved method for separating silver from lead". It exploited the fact that in molten lead containing traces of silver the first metal to solidify out of the melt is lead, leaving the remaining liquid richer in silver. Pattinson's equipment consisted basically of nothing more complex than a row of up to 13 iron pots, which were heated from below. Some lead, naturally containing a small percentage of silver, was loaded into the central pot and melted. This was then allowed to cool. As the lead solidified it is removed using large perforated iron ladles and moved to the next pot in one direction, and the remaining metal which was now richer in silver was then transferred to the next pot in the opposite direction.  The process was repeated from one pot to the next, the lead accumulating in the pot at one end and metal enriched in silver in the pot at the other. The level of enrichment possible is limited by the lead-silver eutectic and typically the process stopped around 600 to 700 ounces per ton (approx 2%), so further separation is carried out by cupellation.
  The process was economic for lead containing at least 250 grams of silver per ton.