Forging, blacksmithing

Not sure what kind of abuse their tools landed, honestly. Most hand tools, when used properly, won't fail. The adjustable wrench that I saw fail had a flaw at a critical spot in the wrench, right where the head met the upper jaw. It would have probably survived elsewhere in the part. Solid carbon deposits aren't the issue, so much as the heat that they cause and change the elasticity of the metal on a molecular level around that spot and create a tension area, like tempered glass that is heated in one spot. It won't break until it begins to cool, because it shrinks, unevenly.

If the dross was removed and the metal kept clean from the original pour, with a good flux, even something like baking soda would help degas and also float any charred junk to the top to have been poured or spooned off with the rest of the dross, I think they probably did something simple like that.

If you really want to put an inexpensive and nice finish on your knives, right before final hone sharpening, look into setting up for parkerizing.

They do this to camshafts and it is a common dark finish on high carbon steel blade shanks to keep them from rusting. gun bodies and barrels often have this finish as well and gives the color to the look of what is known as gun metal.

It can be done on your stovetop with manganese phosphate solution in a stainless steel pot of boiling water. It is not very toxic, either, because you are just dealing with metals. It can be oiled after and takes very nicely to it, or left matte.

There are lots of places that make parkerizing solutions or you can make your own. Google it. I'm likely going to finish some of the steel stuff that I'm working on with this method, along with my anodizing, when I get my alumuminum parts in a finishing stage. I really want to do some parkerizing on a few things, though.