Here's what I was sent by my customer:
If I had to guess this hammer was hardened when it was originally made and it was just a little to brittle, but since it is off of an original that is over 100 years old, I would say it held up well.
To start with I clamped it back together and then took a rubbing of the engraving, as well as about a dozen close-up with my digital camera. I knew going into this that I would end up destroying the engraving and it would have to be re-cut, and would have to be re-cut well enough to not look odd when it is back on the gun.
With it clamped together I then used a dremel with a thin cutoff wheel to grind a bevel in the back side and clean up the rust and metal around the repair, I then tacked the backside together with my TIG, then I made sure it was still tight together on the face side and proceeded to grind the rest of the way around the repair. Once I had it all ground I tacked it in a couple places so it couldn't warp and proceeded to weld it all back in, I was careful not to get any undercut and I welded it so that I was proud of the surface so I could file it down to flush. While it was still hot from the weld I use my torch to bring the whole hammer up to annealing temperature, and then stuck it in my lime bucket and let it cool.
With it all filed and reshaped you will notice a pretty good amount of the engraving is missing. This is were the rubbing and pictures helps, you can make a transfer pattern from the rubbing and the pictures give a good visual reference to re-cut from.
Once I had the engraving re-cut, I had to make the repair look as old as the rest of the hammer. I left a few pits around the repair area, so that the surface would match the rest of the hammer. My personal favorite for making rust and giving that kinda auburn color underneath the bluing is Mark Lee's express blue, use it just like the directions say, but don't boil it, instead when you get the color of rust you want, just neutralize it with baking soda/water.
This is one of the few place that I actually Oxpho blue on a gun for a permanent finish, the reason I use oxpho is for two reasons. One I don't want to boil the part and ruin my nice rust job by turning it black and two oxpho can be applied and carded back over and over again until you get it to match the rest of the finish and it blends in. And this is what you get:
Hope this might be a benefit to someone.
Colin