Most of it washed off with water and scrubbing, but there's still a
red stain all over inside that wouldn't come off with gunk or lacquer
thinner. This is definitely not rust.

Probably a mineral pigment. Run it with a slurry of quartz sand and pool
acid.

Cosmetics are the most common, base, and ordinary things dressed up to look
glamorous. Basically ground up rocks mixed with grease. The essence of
the business is to create an illusion of elegance, when the physical
reality is the opposite. Best not to think about this too much.