Backyard forging Part 3: Tempering the blade & Those final adjustments

Previously we have discussed how to hammer out a knife blank on a backyard forge and then profile both the shape of the knife and the bevel.

Now it is time to harden and then temper the knife so that the metal has the specific properties that are required for the rigors of field use.

 Forge being raised to temperature. Knife placed in the centre of coals

Make sure that the forge has reached a good hot temperature before preparing to harden the knife. Once you have established a good bed of coals, place your knife into the centre and maintain a good airflow to maintain the temperature. After 10-15 minutes the blade and part of the tang (aim for the whole knife ideally) will be glowing a bright red. While you waiting for the blade to reach the correct temperature, prepare the oil for quenching the blade. Find a small metal container, such as a large bean tin or metal bucket and fill it with enough oil to cover the knife. Do not worry too much about what oil you use. There is a lot on the internet about motor oil and its benefits but from my reading vegetable cookinTo carry out this stage we are going to need to use the forge again.g oil works just as well and is inexpensive from the shops. The key point is that oil will cool the metal slower than water giving the desired hardening.

Once knife is glowing cherry red remove with tongs

Once your knife is glowing a bright red carefully remove the knife with you pliers and once the colour of the metal is a cherry red, quench the knife in the oil. Allow the knife to cool completely in the oil before removing. This should take around 5-10 minutes, but make sure it is cool before you try to handle the blade. If in doubt continue to use the pliers. This will leave the metal of the knife hard but too inflexible for field use.

Quench knife in oil as soon as blade has reached cherry red

The next stage is to reduce the hardness of the blade through the process of tempering. For this we need to heat the blade to 200⁰C for one hour which will turn the metal a ‘straw yellow’/ gold colour. This sounds like a strange description for a colour of metal but trust me that it is exactly what it looks like. This is a stage that is difficult to achieve on the forge as it requires a lot of experience and maintenance of the coals to keep the knife at a constant temperature. There is however an easier way to achieve what we are after and that is to use your oven. Set the oven to 200⁰C or Gas Mark 6 and once it is up to temperature, pop the knife in for an hour’s baking.

After the knife has been at 200⁰C for an hour it will take on a straw yellow colour

I appreciate that this might not seem in keeping with the spirit of blacksmithing but when I started out I was more interested in finishing up with a working knife rather than being a purist. A knife produced entirely on the forge is something to aspire to, not to start off with.

After an hour in the oven, remove your knife and you should be presented with one that has taken on a straw yellow/ golden hew. This will indicate that the knife is fully tempered and ready for the final stages of handling and sharpening.

These final stages will be cover over the next instalments until we finish with a fully functional knife you can really call your own.

Good luck with the tempering and just like the forging and reduction, take your time and enjoy the process.
Danny Hodgson

Reference list:

–          Knife Talk II: The High Performance Blade By Ed Fowler  – Krause Publications 2003

–          Pathfinder school video:
https://www.youtube.com/watch?v=p3h-wTjojtY&list=PLZLagqylZ3j7H2MEDrDTb7Dz6xVZeMRTt&index=11