Thanks for that Imas.
I suspect that you are not getting the blade nearly hot enough.
I suggest that you hold the blade with your bare hand about halfway along the blade; when the blade gets too hot to hold, stop heating. By "too hot to hold", I mean that if you hold it any longer you're probably going to finish up with a sore hand. You do not stop heating when the blade only gets warm. If a blade is fixed with either jabung or shellac, the level of heat required will cause the jabung or shellac to bubble from around the base of the hilt, or mendak if one is fitted.
When you grip the blade to work the hilt back and forth and to press it off the blade with thumb pressure, you need to use a lump of old rag to grip the blade, if you do not, you will burn your hand, or cut it. It is possible to exert quite a lot of force by pushing your thumbs together, so if this is how you are doing it, the force should be sufficient.
If you feel that your hands are perhaps not strong enough, you can use folded newspaper to protect the blade, and clamp it into a vice. By "folded newspaper" I do not mean one or two sheets, I mean half an inch or so of tightly compacted paper on each side of the blade.
Ten minutes may or may not be long enough, you need to judge the heat by feeling it, and I've told you how to do that. The time is not critical. The regimen of repeated heating and cooling over a period of days is only resorted to with a hilt that is very difficult to remove, and we normally only find these on quite old keris. The most difficult hilts I have had to work with were ivory on old Sumatra keris. These were all very difficult and took a long time to release. Jawa and Madura hilts I have never encountered any real problems with, they normally let go at the first attempt.
If I were doing this hilt of yours, I would not use foil, however, if you feel that it gives you more confidence to use, by all means do so, however, I suggest that you limit the foil cover to only the bottom part of the hilt, so that your bare hand will grip the bare wood, and you can feel the heat through it. This is a small hilt, you do not want it to get too hot, you cannot feel how hot it gets if you cover it.
To return to the subject of heat.
When we heat treat steel to harden it, we take the temperature to a cherry red, this equates to around 700degrees centigrade. That is hot. It will burn right through your skin and flesh. When the steel is hot we cool it suddenly by plunging into oil or water. After this the steel is hard, but it will break easily, so to make it able to be used we draw some of the hardness out of it. To do this we gently heat the steel again until it shows a colour on the polished surface of straw or blue, or what ever colour we need for the purpose that the blade will be put to. You can see this colour change effect if you sharpen a chisel on a grind stone, if the chisel edge starts to go blue you'd better dip it in water immediately, or you'll have a soft chisel.
OK, so you can see that to get steel hot enough to make it soft, you've got to get it very hot. To get a blade hot enough to make it soft you need to leave it sitting in a working fire for a length of time. It is totally impossible to make steel hot enough to soften it in even the slightest degree with a candle.
Additionally, a keris blade is usually only hardened at most up to about three quarters of its length, it is not usually hardened at all in the area of the sorsoran.
A keris blade is made of iron and steel, the steel is a thin wafer inserted between two layers of iron, even if you get the outside of the blade very hot, the steel core of the blade will not be as hot as the outside of the blade. Steel contains carbon and that allows it to be hardened. Iron does not contain carbon, and cannot be hardened. You can heat iron all day long, plunge it into water, and it will still be soft.
It is impossible for you to do any damage at all to your blade by heating it with a candle.
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