i tried makin my own the ferst time ..i bought a couple small stripes of pure silver and  tried but it dint tern out to well,,,so i got into amazon.com/..they have a lotta diff kinds and ppm's...if your gonna use the colloidal silver a lot then ya can buy the concentrate ..i buy the 16 ounce 240 PPM silver mountain..has a long shelf life..i keep it in frig...i mix it with distilled water to get it to bout 50 PPM..they say 30 PPM is ok tho...i use one those small 1 ounce measuring cups hospitals use..1 those small cups of silver to 5 or 6 of those with distilled water..i just eyeball it as to how far i fill up the measuring cup..usually get it bout 50 PPM..i use meter to check it tho...used to be able to buy the 8 OZ bottles..

Colloidal Silver Concentrate