This is a long shot, but well-known numismatist, George H. Clapp, is recognized as a pioneer in processing aluminum.
Could it be a bar of aluminum before or after processing that was at the time known as "Clapp's Metal" ? Cross check
info on George Clapp & aluminum & you might find something helpful. Good luck !! J.T.G.
Here's an interesting link: https://www.coinbooks.org/esylum_v19n26a24.html
Notice this from the link: "Before World War II, Alcoa was the only producer of aluminum in the United States, though there were many companies which manufactured products from aluminum. In the 1890's Alcoa was hoping for large orders for aluminum sheets or bars"
Sheets or"bars" Maybe an early bar from Alcoa?