Hatters used mercury, not lead.

I knew a person who suffered from lead poisoning (long term occupational exposure).

She wasn't aggressive in any way, just not really "here".

Did she ever get better?

Unfortunately not. Or, any chance for that was lost when she had a stroke.

Lead is needed for the brain. The person is fully there (in fact more than before) they only stop uncontrollably reacting to everything, and stand straight, instead of being all wobbly.

I think you're confusing lead with mercury for the hat-making connection.

why do you need either of those for making a hat?

When felt was made from animal fur, it made it easier and less gross the remove the hair from the hide and soften it.

Previously, urine was used.

Yikes. Knowing what we know now, is mercury the worse option?

It depends. Urine is not pleasant, but is usually safe to work with. I’d rather smell than suffer brain damage. :)

shiny when applied to silk.

Mercury and lead poisoning have similar effects.