I just use use nitrohydrochloric acid. It's just nitric acid and hydrochloric acid (preferably in a 1:3 ratio). It's one of the only acids capable of dissolving gold, and gives off chlorine gas and nitric oxide, which then oxidizes into nitrogen dioxide. The apothecaries of medieval times would use aqua fortis (a liquor made of saltpeter), vitriol, and salt. Fun fact: saltpeter can be made from pigeon sh*t