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Originally Posted by kronckew
Nepali Kamis (blacksmiths) routinely heat treat their blades with boiling water as a 'coolant' from a tea pot on the critical heated edge to harden that, leaving the residual heat to temper the spine a bit softer. It takes them years of practice to learn how to do it right..
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I would imagine that the method works better on short, relatively wide single edged blades than long narrow ones. And having polished a few antique kukris in my time, the technique worked well. Edges were respectably hard, spines softer, and with a minor etch and rub-down afterward with very mild abrasive powder, a nice cloudy "temper line" can be seen.
A friend who makes knives once traveled to Thailand to see contemporary makers of daabs and other blades at work, and he reported that smiths use a rather long trough-like forge so that the edge side gets hotter, and they quench by immersing just the edge in the water bath, being careful to include the point on long curved blades, and then after some moments dunk the entire thing underwater. As you describe, it's all about technique and timing.
19th cent. Victorian writers have a low opinion of Burmese blades, but I've found, from actual polishing, that the better ones have a very precise and crisp
hamon with a line of crystallization that is comparable to a lot of Japanese work. One would think that some sort of clay heat-sink,
à la japonaise, was used but I've not been able to verify this. BTW, the use of these clay coatings was mentioned by the Persian scientist Mohammed bin Ahmed al-Biruni in his treatise
On Iron (10th century) and highly visible differential heat treat is evident on wootz
shamshir blades made in Iran through the 18th cent.