I have been collecting marbles from spray paint cans ever since I was a kid. I currently have 300ish spray paint can marbles and I had about 100 stolen from my car years ago; I suspect I have personally opened over 400 cans. I can validate many of your comments.



First: Metal balls, usually with a flat spot on opposite sides, come primarily in primers and very small cans. They rust, yes, but only after having been exposed to the air. While in the pressurized can, full of paint which would solidify if it was exposed to air, they are fine.



Second: You normally get only one marble, some cans have two. I have never found a certain brand that always has two.



Third: Yes, they can be dangerous but you can open, semi-safely, a full can. They can fly out of your hand though as they act like a large, angry, directionless, heavy bottle rocket. The can doesn't explode though. It is unnecessary to spray out the remaining pressure, but you can if it makes you feel safer.



Lastly (fourth): Yes, they are glass marbles. They seem like marble "seconds" as they are usually not totally spherical and some have grooves in the glass. I have found very few opaque marbles which were not black. Many have bubbles throughout them. Blue is the most prevalent color.



I made a special tool out of a piece of 1.5" angle iron that I use to open the cans and extract the marbles. It is also beneficial to have a pan of paint thinner or stripper to drop the marbles into upon their birth into air as it is awfully hard to remove the paint once it has dried.



On a personal note. It always disturbed me that there were no other people who collected the marbles from spray paint cans. It is nice to see that there are at least a few people with the interest.







