I had a gal say she couldn't get the Dollar Store safety pins to rust , because they have a coating .
I do not have that problem and offered up advice along with another gal who uses them also .
I use an aluminum pie pan , peroxide , Vinegar , salt and a shot of bleach . I do this outdoors due to bad chemicals . I place my pins in the pan and add 1/4 cup of the vinegar and 1/4 cup of peroxide , a tablespoon of salt and a tablespoon of bleach . Set in the sun and leave them alone . I also add old leaves to the mix when I want them grubby . Adding the leaves , makes them rust and turn black with bits of grubbies . Try it and see . (-: