Try to stay away from Silica and especially Play Sand. Very hazardous to your health. Can and does cause a lung disease called Silicosis. Go with Black Magic or some other media. Also try blasting at an angle instead of straight on your part. Works good and don't embed it in your item. These things, I've learned from these fine people on this forum.
see this web site for more info:
http://www.silicosisfyi.com/