The MDS is saying 40-50% Amorphous Fused Silicon Dioxide. I guess that is not the same as "free silica." Does it become free when you blast it? I confess I am not knowledgeable on this subject. EDIT: After some reading it seems that crystalline silica is the dangerous form. Amorphous silica has far less if any respiratory risk. Both of the products Kelly and I listed have amorphous silica. I am not particularly worried about silicosis at hobby level exposure but its good to know what you are working with. Robert
