You didn't say when your Mod 21 was made but Win changed to hot blue process right after the war all the receivers were hot blued no mention of carbonum bluing as an option. Personally I think collectors are too far out trying to recreate obsolete blues, carbonum and niter included. Who really cares excpet a collector and the reblued gun isn't original anyway. I have a prewar 21 all original and the receiver looks the same as one made in 1960 and factoryhot blued. As I recall carbonum is done with a higher heat process and the smoke from the mixture does the coloring Sounds like alchemy to me. I'd rather plain old hot blue. Just send to to Tony and you won't be sorry.
