Help: Freddy Glove Coloring Question

[🪦 mpetrie ●]

I pretty much already know all the chemicals to change the surface of the copper to different colors except for this one method I'm asking about. I'd just like to expand my different methods of aging so I know how to get specific looks and I really like the color of the fingers on the glove pictured above so that's why I'm trying to find out only what this stuff is or how it's applied.