A few thoughts on hardening frizzens.
First off, most of the frizzens on well made locks are just fine as they are.
When people get a few klashes, (the sound of a flintlock flint hitting the frizzen without igniting the pan powder when it's fired) the first thing they think of is "I bet my frizzen is worn out!"
More than likely, the fault lies with the flint. Perhaps it is dull, or it moved the last time the gun was fired, or it's oily, or fouled. Perhaps the priming is damp (or wet), or perhaps the prime is made using crappy powder, or perhaps it was just one or two of those times when the hot sparks didn't hit enough powder to lite it.
Believe it or don't, but sometimes it is just because the guy trying to shoot the gun forgot to prime the pan??
In any case, if the frizzen once threw good sparks, it should continue to do so. There is a lot of surface area on the face of a frizzen and they usually don't wear out.
I've even heard of people firing thousands of times and going thru hundreds of flints, but the frizzen continued to work. These frizzens are usually made out of high quality "thru" hardening steel so, they do not have a "case" of high carbon steel on their faces. They are hardened all the way thru.
There are some inexpensive frizzens made from low carbon steel in the world.
Low carbon steel will not harden, and it will not make many sparks. These frizzens do require "case hardening" in order to put enough carbon into the surface so it will be hard enough to throw good sparks when it is hardened.
As Bushwhacker mentioned, if you try to file the face of the frizzen, the file shouldn't make much more than a very light scratch, if any mark at all.
If it (the surface the flint hits, not the forward surface) is soft enough to file, it needs to be case hardened.
I would suggest you either take it to a gunsmith to let him case harden it, or you use Kasenit.
Kasenit is a case hardening material which is very inexpensive and easy to use. It is not poisonous and does not give off harmfull fumes (that I know of). It can be purchased from Dixie or several other muzzleloading gun part suppliers or places like Brownells. One package will last most people a lifetime.
To use Kasenit you need a propane torch, a pair of pliers, a can to hold the quenching liquid.
PUT ON YOUR SAFETY GLASSES.
Holding the part with the pliers, heat it until it is bright red hot. Stick the part into the powdered Kasenit so the surfaces you want to harden are totally buried in it. The Kasenit will melt and adhere to the hot surfaces. You don't need to harden the area of the frizzen which covers the pan, and you don't want to harden the screw hole so don't worry if these areas are not coated with Kasenit.
Reheat the Kasenit covered part with the torch until it is bright red. Hold it in the flame, moving it just a little bit so the entire area of the frizzen is a uniform bright red. The Kasenit will seem to melt on the part. This is good.
Keep the part at this red temperature for at least 2 minutes, 4 or 5 is even better.
It doesn't hurt if after 2-5 minutes, you re insert the area into the Kasenit and get it to recoat the surface. If you do this, you will have to reheat it to the bright red color and hold it at that temperature for another 2-5 minutes.
While your holding it there, you can imagine what is happening right before your eyes. Little molecules (I spelled it right this time :: ) of carbon are actually penetrating the surface of the steel and mixing with the steel to form high carbon steel! The longer you keep it at the bright red temperature, the deeper they go. Isn't that amazing? ::
OK, Now that your pliers are getting too hot to hold, you need to quench the part.
If you screwed up and your part is REALLY a thru hardening steel (that didn't need the case) you MUST quench it in OIL! If you quench a thru hardening steel in water, it will often BREAK into pieces from the shock of cooling too fast.
For this reason I am going to suggest you quench the part in oil first.
To quench the part, while it is still bright red hot, rapidly move it over to the can of oil and drop it in. You want to do this fast! You want the part to still be red hot when it hits the oil.
When it hits the surface of the oil, the Kasenit usually breaks off of the part with a loud POP!!! sending pieces of the coating and some oil flying. (That's why your wearing the safety glasses!!). Let it cool in the oil for a while and fish it out.
Take your file and try to file the case hardened surface.
If it is to hard to file, jump to the tempering area below, or just read on so you'll know about water quenching.
If you can still file it, you have a low carbon steel part which didn't harden fully because you oil quenched it.
All is not lost. Dump out the oil and fill the can with water.
Cool off your pliers and grasp the part again.
Reheat the part to the bright red color and hold it at that temperature for at least 15 seconds (longer won't hurt it).
Now drop it into the water.
This time, I almost guarantee it is harder than a groom on his..well, we won't go there.
It will be hard! Too hard!!
Using some 600 grit black wet/dry sandpaper, lightly sand the part to remove all of the black oxides/Kasenit that is still on the part. You want it fairly shiny on the surface the flint hits.
Tell your wife your not going to hurt her oven in any way, but you reeeeeeeely need to use it. Promise her that if you break it, you will take her to dinner ::
Now, set the oven to 450-470 degrees F and let it heat up to temperature.
Place your frizzen on a cookie sheet and place it in the oven to bake for 20-30 minutes or until the crust is nicely browned.
Just kidding.
Just bake if for the 20-30 minutes, take the cookie sheet and the frizzen out of the oven and let it air cool to room temperature. The face of the frizzen should be a very light yellow color.
The process is done. Sandpaper it and re-blue/re-brown or just leave it as it is. :: ::
If your going to try to use up all of that Kasenit you might try hardening the heads of your guns screws and other things that Viagra won't help. If you know for sure the part is plain old low carbon steel like screws, go directly to the water quench. Do not bother with the oil quench because it won't work. (Once again, do NOT water quench most thru hardening steels unless they don't respond to the oil quench method).
As for the leather in a tin can method, it is not real effective unless you can be assured the leather (or pieces of it) are in intimate contact with the surface you wish to harden, WHILE the whole thing is heated to over 1400 degrees (bright RED hot) for a period of 10 to 15 minutes.
To do this, you really need a good pile of charcoal and a fan to blast it with and keep it up to the high temperature the process needs.
The idea of the closed can is to keep the free carbon released from the leather at this high temperature from oxidizing (burning) so it can penetrate the surface of the steel.
Because the little carbon molecules are floating around inside the can, they can penetrate areas you really don't want case hardened, like the thin walls where the screw hole is.
The big guys in industry copper plate the surfaces they don't want hardened by the free carbon, but that's not an option most of us have. This and for other reasons, I really don't recommend this method.
Spend a few dollars and buy some Kasenit. You will be glad you did. :: :: ::