Hi Tatyana. I use lab grade arsenic trioxide, but i know that it isn't an easy substance to come by. The nice thing about it though is that it is always the same so you can get more controlled results. I have never used realgar, but i have heard from members here who have that you want the pink stuff. But the white stuff might work just as well.
I don't know anything at all about "sterling arsenic" so you might want to stay away from it.
