A few years ago I had 22 unofficial LRB's analyzed using a scanning electron microscope. These coins were all VLPP's copying the Siscia mint, which minted this type from A.D. 318- 320. My hypothesis was that the metal used to mint these coins had come from melting down the previous demonetized issues, like SOL and IOVI issues. I was expecting to see less than the 4% silver average of official VLPP's; somehwere around 2-3% silver and that was what the results showed, except for one coin that only had an alloy of copper and lead. The results show the percentages of copper, silver, tin and lead. These results do not show any trace elements of less than 1% though.
I have a page that shows an analysis of some official coins-
http://www.constantinethegreatcoins.com/metallurgy/you can see all the coins and their percentages on this page, near the bottom.
http://www.constantinethegreatcoins.com/barb2/below is one of the coins (#5) with the SEM data.
