Ha! Soda cans. I did that once at a party. Put some haze on it. It was electric haha.
Tinfoil will give you Alzheimer's sooner. Cannabis fights this though so that's a counter balance. Metal shavings and shit is never good and same with galvanized screens but those are stainless steel screens in those grinders.
Scrape the keif out. You could run a magnet over it to pick up any small shavings within the pile.
Plastic haha. We used apples and fruit. Imagine a hemp plastic bowl. If it burns it's ok, it's organic plastic you can inhale once, it will not harm you unlike plastic smoke.
What about the plastic ones?
Do they make grinders out of hemp plastic?
I have a few things made out of hemp but never seen a grinder?
your alzheimers comment...talk about misleading