Forging last metal, or forging the head in this case, is a method of manufacturing steel. In order to get proper penetration of the material, and therefore a proper build up of carbon and other alloying elements, you need to make sure that your forge has a certain amount of initial heat input. The reason being that if you don't put enough heat into it on the beginning, you won't be able to add as much on top
The best way to do this is by using a forge that has an adjustable fire box. This will allow you to adjust the amount of heat you put in at any given time so that you can control how much carbon and other elements are added to each piece of steel.
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