Amazing they had this figured out by the 1600s. Four Iron Crolle Miquelet barrel reported to have been found during excavation of a dump site in Germany



BTW: the Hohokam decorated shells by etching them with citrus juices.

"From Art To Science. Seventy-Two Objects Illustrating the Nature of Discovery" Cyril Stanley Smith
p. 15
The etching of surfaces by the application of corrosive substances to produce decorative effects, a deliberate mode of “weathering,” was practiced as long ago as the third millennium B.C. in India...Perfected in the armorer’s art in Europe, the technique of etching was more pacifically applied by the American Indians of the Hohokam culture, who used acid fruit juices stopped by natural resins to decorate seashells.

Interesting stuff
https://docs.google.com/document/d/1me32b1AZQqr361CVtb-jeAoK1hDO2ZT6QR1fXQkjY0c/edit

https://sites.google.com/a/damascusknowledge.com/www/home