How pure do alloy components need to be?

Hello everyone,

I have alloyed silver successfully for months and have had mixed successes with gold. I have made workable 10K yellow and a very crack-ey 14K rose. I used copper electrical wire from the hardware store for both. My question is how pure must the alloy components need to be to produce nice, workable gold alloys. Gold is typically sold at .9999, silver is either .999 or .9999. I have found riogrande’s copper wire is .999 pure copper with 0.04% oxygen. The oxygen shouldn’t have any effect on the finished gold being brittle, even fine silver rapidly absorbs oxygen when molten (if you have ever melted fine silver and see little things that look like sparks coming off that oxygen coming out).

This appears to have very little scope for contamination of the finished gold, does this sound correct? Are all the materials pure enough?