MacBain and Tempering Questions

Hi!
Can anyone tell me about the Macbain coins and how they are used? I know there is a vendor and the vendor has weapons but what "level" are the weapons? Also can you use the tempering alloy (I think that is it) to temper regular gear? I am having a tough time tempering gear even with high level stones (200 and above that I got in daily logins or events). Is it difficult to find more high level stones? I know there are potions you can buy that increase the success of tempering but are there any other suggestions on how to increase tempering chances?

Thanks!