If you are committed to buying rather than making your own, I prefer Sovereign Silver. I think it's very pure, and the silver particles are tiny and not clumped from what I understand. I use it rather than my homemade with my Silvergen if I'm going to nebulize my silver. I suppose I might not need to, but I just feel the need to be more cautious with purity and particle size when I'm taking it into my lungs. You can get it at many health food stores, or google it on-line.