I don't have any idea of how old a can one would have to have but upon my first introduction to casenit some 50 years ago it has always been stated to be Cyanide Free. I have also seen references to, but never further investigated, that one of the chemicals used in film development could be used in the same manner as Casenit.
For those not familiar with temp conversions those temps given in the referenced article in "C" convert to 1454°F to 1688°F.
It should be noted that heating in this very same bath to 1200°F, while it may give a good color will not harden the part but will in fact draw its temper very close to its fully annealed condition.
