Making a small ax/wedge to use when splitting wood for handles. From a rusted old ball peen hammer (pre-1950). Still have some polishing left to do although will leave in the black when done, not all shined up. Thoughts on the best heat treating approach?

Depending on how tough it is you might want to try using it with it normalized and see if it actually needs to be hardened. Unless you're going to be using it to split some kind of super hard exotic woods or splitting off large pieces of hardwood you'll probably be ok without a harden and temper if the hammer was made from decent steel. 

Thanks Michael

I don't really have the experience with axe heads to answer this one, but I would have thought bringing the edge area up just past the transition temperature (look for the shadows) and a heated canola oil quench would work pretty well.  Temper it a couple of cycles at increasing temps until you get to where it can just be sharpened with a file.

Of course, this assumes a lot about the steel the hammer head was made from...

Did a heated safflower oil quench of the blade (1/2” or so). Here it is....fun little splitter:

 

 

Neat.  I keep meaning to try something like that to make a kindling splitter for the camp fire.  I should start looking for a old hammer head!

I use the heated Canola oil treatment after a couple of normalizing cycles. Works great on American ball peens.

 

I'll have to send you some of the old cast iron American ball peens so you can show how it works great on them! (perhaps adding "most" as a prefix to American would be more accurate...)

Gee! Thanks for the sarcasm Thomas! I wish I were as perfect as you!

"Most" Anyone would obviously omit the cast iron ones...  

 

I didn’t know they even made ball peen hammers from cast iron. 

Nor did I. One would imagine it would not make a very effective hammer. 

The thing is that everything back in history was not the greatest; they had a lot of low grade tools back then as well; they just didn't survive into modern times.

Remember the case hardened knives for the Indian trade here in the Americas?  (Why they tended to use a chisel edge as sharpening it would always have the thin steel layer for the edge where the double bevel would remove the steel and leave iron.)

Even in more modern times the 1897 Sears Roebuck catalog offered blacksmithing equipment in several different quality levels; and in modern times I can remember getting a cast iron claw hammer back in the 1970's as a cheap throw away that soon broke and was thrown away...probably made to hang a picture in an apartment, NOT to drive nails for construction.

Testing your starting materials was considered a basic blacksmithing skill, (Moxon describes testing stock in Mechanicks Exercises published 1703), and if you work off the scrap stream like many of us do you really need to test as well---I remember how flabbergasted I was the time I got a leaf spring that could NOT be quench hardened! I wish I had tested it *before* spending the time forging it into a blade...