Actually, he didn't remember if lye was that strong, but it was good to keep 'Melon Face' on alert.
He boiled off about two-thirds of the water.
Ma Lin waited for it to cool.
He chatted slowly with 'Melon Face'.
Then he dipped two fingers of his left hand into it a little, indeed feeling very slippery, but not painful.
He took them out and, with a pinch, shed a layer of skin.
It indicated that the concentration was sufficient.
Ma Lin showed the sloughed skin to 'Melon Face' and said, "If the concentration were higher, it wouldn't be just skin peeling; the fingers would be severely burned."
Then he took a piece of fat, melted it in a bowl, and mixed in some lye.
Soon, solid matter began to form, and he gradually added more and more lye.
He controlled the heat so that the temperature was neither too high nor too low, just enough to keep the fat liquid.
As for how to control it, he used a smoldering fire and placed the bowl a little further from the fire.
