A vintage 1980 packet of sodium carbonate cleaner. This was provided by Spring Ag Switzerland with their new copper cookware to dissolve the factory protective film on the copper.
We found this with a plastic bagged au gratin pan - new old stock. Most copper cookware makers had some sort of protective factory film or lacquer, that had to be removed before cooking with the item.
With this product, one would first dampen the item with hot water, then polish with damp cloth and this powder.