Sometimes a frizzen (old frizzen, either original or early repro) just won't harden as the surface doesn't have enough carbon. So you replace it, or case harden it, or just say to heck with it and half-face the frizzen and be done with it. Frizzen hardening--old school backwoods style--is voodoo. Souds simple: pack it in bone meal, crimp a metal can around it, and cook it in a fire.
Except. . . . first off, you have to make sure your fire is hot enough but not too hot. Then the whole "crimping of a metal can"--you want it airtight, nobody ever told me that. A Prince Albert can won't work, the frizzen won't fit (and if it is a tiny frizzen for a pistol lock and does somehow fit, it won't be hardened because it is in contact with the sides of the can. What works really good is a 1 pint paint can--unless it burns through the side. One of those fancy tea canisters with the slip-fit lid works well too, and the metal is a little thicker.
And bone meal--like a gardener uses? Too fine. Crushed bone doesn't work either, but coarse raspings from a bone work--but not a fresh bone, and not a cooked bone; try to find one from a cow that died about 2 years ago, with the bones aging in the pasture so the grease is gone. It takes a lot of bone to rasp down to tightly fill a 1 pint can. And it works better if about half your "bone meal" is actually bone charcoal--OOPS, now you need about another pint of bone meal. Ever made charcoal from bone? The smell is awful, and gets everywhere.
So you mix about half-and-half of your dry bone raspings and your stinky bone charcoal, until it looks like grey dirt. Fill your can about 1/3, tamp it slightly, bring the level up to half. Set your frizzen in the can, centered away from the sides, and press it into the fill. Bring the level up to 2/3, tamp lightly (don't shift the position of the frizzen). Fill the can, press it down, re-fill, repeat a couple times. When you put the lid on it should slightly compress the fill.
"Cook it in a fire" is a joke. Push your coals in a pile in the middle of your firepit, and make a hole big enough to set the can in. Put one of your fire irons next to--but not touching--your can. Shovel more coals on top, add some wood to your fire because you need more coals. That fire iron is your "thermometer". If it gets sparkly-white-hot, too hot. Dull red, too cold. Keep it just under cherry red for about 30-45 minutes, then let it cool. When cool, dump the ash and your frizzen from the can. Clean up the frizzen, double-check with your lock to make sure it hasn't warped, then harden and anneal it.
I've done several frizzens like this, and it always works (we won't discuss the failures that lead up to this process). You know what else works? Anneal the frizzen, grind it clean, fit a piece of a file to match the curve, rivet it in place and sweat it on with 50:50 solder. The soldering heat will anneal the file new frizzen face just about right. I haven't rasped bone since I learned to do this.
About 90% of the time, on a new lock that won't spark you can just re-face the frizzen on a 6"-7" grinding wheel (depends on the size of the frizzen). Don't take off too much. Sometimes the surface is de-carburized in the hardening process. If that doesn't work, re-harden it quenching in oil. Not hard enough, try again but quench in brine. Once it is hard, anneal and polish.
