We spotted this article on blackening metal parts (brass) that Amati shared on Facebook today. This is a pdf article posted on the website of the Midwest Model Shipwrights, a long time Chicago based ship modeling group.

Check out the article here: https://midwestmodelshipwrights.com/pdfs/Blackening%20Metal%20Parts.pdf 

This is an interesting and active ship model club. So, while you’re at it, check out their information filled website here: https://midwestmodelshipwrights.com