[A. G. Maisey]

Re heat treat.

For simple forge heat treat, the heat treatment of a spring and a blade is the same, the only variation is the colour to which it may be drawn, and even that does not always vary.

In simple terms, after annealing, you heat the object to be hardened to critical, which can be most easily detected by testing with a magnet:- when the magnet does not grip the object it is at critical temperature.

The object, either blade or spring is then plunged into the cooling medium, which may be water, or oil, or brine, dependent upon the steel to be hardened.

After the hardening the temper is drawn. There are a number of various indicators used by traditional blacksmiths to gauge the correct temperature, for a spring, some old timers would run a piece of hardwood down the object and gauge the temperature by the colour and character of the sparks thrown off.

The usual textbook method is to clean off the surface to be drawn, and re-heat the object until the correct colour for intended hardness shows, then cool the object again in the cooling medium.Different levels of hardness are required for different purposes.

As noted, a keris blade, and many other blades, are laminated, and in the case of a keris, only the projecting edges of the blade core are homogenous steel, the laminations that sandwich the core are irons of various qualities, or iron + nickelous material. This is the reason I wrote:-

A keris is also heat treated, but with a keris, because of the laminate construction probably only the hardened edges of the core will react in the same way as a spring, ie, they must become brittle.

The heat treat of a keris blade is not done to relieve any tensions.

The blade would be annealed to relieve tensions, not subjected to a heat-treat to relieve tensions.

However, a keris blade is carved from a forged blank (bakalan):- most of what we see in the blade is produced by stock removal, and during this process the blade may have been returned to the forge several times prior to heat-treat. By the time it actually gets to heat-treat stage there is probably not much, if any, tension to relieve. Put it another way:- I've made a few keris and a whole heap of damascus and plain carbon steel blades. I always annealed the damascus and the carbon steel, I never annealed any of the keris I made.

Some keris blades can be bent, but not necessarily all --- or more precisely, not necessarily all blades can be bent in the hardened section of blade; since hardening of a keris is only for part of the length of the blade, they can all be bent in the unhardened section.

The temper is not drawn in a keris blade, it is simply plunged point first into the cooling medium. End of story. If the laminations are the traditional irons or iron and nickel, yes, you can bend the hardened section of the blade a little without too many concerns, however, if steel has been used as a laminate material it may or may not bend.

In the damascus blades that I made I did not draw the temper in small blades, like trout/bird blades, but in other larger blades that could conceivably be used for chopping I did draw the temper. The reason I did this was because the small blades were intended only to cut, and if the temper was not drawn the edge would last longer, but the bigger blades that might be used to chop could gap if the temper was not drawn, and that edge would not hold as long as the small blade edge.

Emanuel has given us a link to additional information as to exactly why this cracking can occur. I do not fully understand what I've read, but I think it comes down to :- ferric material that is hard is susceptible to cracking. Ferric material that is not hard is not susceptible to cracking. But I am unclear as to whether it is the quality of hardness, or the content of carbon that leads to this susceptibility.

In any case, it seems that an old, degraded keris would be quite safe to de-rust using electricity, but a well preserved good quality keris would be at high risk.