AC is not usable for a decent colloid unless you use two gold or two silver electrodes. And even then it may not result in a clean product.
I.e. when I do colloidal gold, the cathode does not stay perfectly clean but will accumulate some gunk, especially around the water level. Now imagine doing this with AC. Something from that gunk may go back into solution. This may be a very unscientific explanation of what there actually is, oxides etc, but I know enough not to attempt this with AC. Use +30V DC for Colloidal Gold, and constant current X mA DC for Colloidal Silver and you're set.
Pure copper should not be considered safe to ingest, as copper is used in body metabolism and will put several other systems out of whack (antagonist in iron absorption). Trace minerals in food are how you are supposed to ingest all the metals that the body actually uses. Copper, iron, zinc etc. Gold and silver are not metabolized (except for some enzymes afaik), that is why they're safe.