What is a forge used for?

Quartz sand

The cheapest and easiest way to get a protective layer around the hot workpiece.

Quartz sand can be found in every hardware store. Should have a fine-very fine grain. Shortly before the metal reaches the stop point (around 1100-1300 ° C, at which the material changes from solid to liquid; like a harder bread dough), the quartz sand is scattered over the workpiece. A layer of glass forms which protects the steel / iron from the oxygen in the air.

If the tinder, which keeps accumulating around the anvil, is finely ground and mixed with the sand, then you can improve the formation of a protective glass skin. 10% scale / 90% quartz sand is a very promising mixture. The quartz sand must be dry!

borax

Borax, is a naturally occurring mineral. In principle, the application works in a similar way to quartz sand.

What changes is the temperature range for application. At approx. 850 ° C, the workpiece is completely covered with borax. This then melts immediately and forms a protective layer. Borax is not as temperature-resistant as quartz sand and is therefore not particularly suitable for "high" welding temperatures. Especially when manufacturing damask, you have to hit the temperature range at the lower stop point very precisely.

Another disadvantage is the health hazard posed by the mineral.

Many cutlers who make damask use borax and often in large quantities (you can watch videos). Since the application is "relatively" easy, this is understandable, but I doubt that most blacksmiths are aware of the hazard.

I also use borax for certain forging techniques and in very moderate amounts.

Loam / clay

Doing the same thing as you did with sand and borax won't work with clay. You can throw a lump of clay into the forge and wait until a protective layer forms. Will not work, but it's worth a try :-)

In Japan, clay is still used very often, especially in traditional forging techniques.

Clay is also found in the coal and you can see the remains as slag cake in the forge. What is lying around as an unwanted leftover can also be used in a targeted manner.

If the very fine clay is dissolved in water and this aqueous solution is poured over the hot forging, the water evaporates and the clay remains as a protective layer. This layer is very robust and you don't mind that much if the workpiece is moved in the forge. Due to the high melting point of clay, you can go to the upper end of the breakpoint temperature, i.e. just before the carbon in the material burns.

This is a very good option for certain forging techniques, although you always have to remember that any high heat during forging worsens the material, e.g. decarburization. This technology will therefore lead to a severe deterioration of the steel in the gas fire, whereas in the charcoal fire the impairments are kept within limits.

Clay mixtures are also used to harden steel. For example, a "hardness line" is applied to blades in Japan HAMON called, generated.

This procedure is very time consuming and requires a lot of experience. Every blacksmith keeps the recipes for the clay mixtures like a secret.

If you ever see a "cheap" knife or sword with a hardness line, you can almost be sure that there was cheating (etching, grinding, brushing, ...). If you are offered an expensive work of art, please have it examined by an "expert". Is just a tip to save money :-)

MOOCit question

Why is borax, clay and / or sand used in the forge?

Borax, clay and / or sand prevent oxygen from reaching the surface of the workpiece during the welding process. If the oxygen is allowed to react with the workpiece unhindered, iron oxide forms on the surface of the workpiece and welding is no longer possible.