funny, I ask similar question days ago.
According to Squidoode, Anarchist wire is the "purest" form of nichrome.
Now, as said above, there is ni-cr 80, 60, 40, 20, etc.
those numbers refer to the percentage of Nickel in the Nickel-Chromium alloy mix; HOWEVER, as youll see on Wikipedia or elsewhere, "Ni-Cr" can be mixed with additional metals... such as Iron (Fe), and some others.. cant remember, maybe Tin, etc.
Now, if Squidoode's statement is not just a marketing lie, then the "purest" form of Nichrome must mean there is absolutely nothing else in the Nickel-Chromium mix. I guess package does say Ni-Cr 80 on it... So exactly 80%Nickel, and 20% Chromium... no tin, or iron etc.
I need to csll temco and see if they can give me specifics on what else may or may not be in their NiCr 80/40... or NiCr 20. I know Temco has 2 kinds, Nicr 80 and one other.