In the commercial absence of Kasenite, I have made & used my own mix.
Basically potassium ferrocyanide mixed with actual wood or bone charcoal. Spelling may be important to your health, the chemical should be ferrocyanide. K4Fe(CN)6 Wash your hands after using the stuff, it might not be all that harmless.
Real bone charcoal contains tri-calcium phosphate. This chemical does two things. First, it speeds up the case-hardening process so that it actually happens. Second, calcium phosphate is what is responsible for "case colors". Don't worry about getting any pretty colors here. This is just a matter of hardening your frizzen.
If you want real good "case colors" read, then study, the two-part article by Oscar L. Gaddy in The Double Gun Journal. Part 1 Winter 1996, and Part II Spring 1997.