David Stone writes:

These were struck originally for presentation purposes as Pollock mentions a request by Henry Linderman to have "two sets of impressions of our coins struck in Aluminum prepared as early as they can be without an interruption to the regular business of the Mint. I desire to send one set to the Bank of England and another to France". Pollock also notes that Linderman asked for 2 more sets 2 days later.

It is likely that some of these were deliberately made for sale to collectors. The first recorded sale of one of these cased sets was lot 1381 of the 1870 Mason & Company sale of the William Fewsmith collection. This set was bought in by Mason and was offered piecemeal in his next sale but did not sell.

The Brand collection had two sets, Woodside's purchased in 1895 and Stickney's purchased in 1907. Newcomer also had a cased set.

To read the complete article, see:1868 Cased Aluminum Trial Set(uspatterns.com/18casaltrial.html)