I would agree with Blah's assertion that this was used for electroplating metals. I'd say it would be short sighted and extremely arrogant for us to assume that we have all the answers for everything in this world. Truth is, even with all of our modern technology, we cannot even come close to duplicating some of the most impressive ancient wonders...the Great Pyramids come to mind. What the ancients knew is both incredible and profoundly vexing.