I have not had time for the hobby for a few years and decided to shake up the paint again so it does not go bad. To my surprise, I found out that the metal balls I bought to put into the paint bottles to make it easier to shake them have started to rust... looking at the bottles from the bottom I can see a big "rust" spot on each. I did not think there was anything in acrylic paint that stainless steel would react on, so I guess the seller on e-bay for the metal balls was not telling the truth The question now is if I should scrap the paint (give it to my kids for painting), or if I should try to save those that it seems have had no change in color. Does anyone know how acrylic reacts when having rust added to the combination? Will it affect anything else than the color? I would really hate spending time painting with the bottles if I could risk that they start chipping etc. on the model after a while.
Sorry to hear that. I've read that happening to others, but nobody went into detail on how it had affected the adherence properties of the paint. Maybe give a couple of the worst examples a test run on a scrap piece of sprue and compare it to an unaffected paint.
I would shave the rust off just to be sure. Normally if you are applying paint to a rusted surface its a good idea to shave it off... but that may just be to get an even coat and to cover it up so it looks good when applied? In the case of the mixing ball, only concern I would really have would be little flakes falling off and clumping in the paint.