Re: Here's the 99.99% pure fine silver wire page for C.C. Silver & Gold in Phoenix--previous link was only 99.9%

.99% is not 'necessary' as you put it, .9+% is perfectly OK.

.9+% would be the minimum purity one should use in their silver, and the amount of impurities in .9 as compared to .99 are so negligible so as not to be worth worrying about, .99 or purer is good, I agree, but it's not 'necessary'.