How does lye appear in ashes? One of the oldest recipes to create lye is this one:


Take well burnt ashes and put them in a barrel
Fill the rest of the barrel with water
Leave the suspension for a week or two
You can now try the lye concentration with egg - if 2/3 remain above the water, the concentration is sufficient for domestic uses
Separate the lye solution from ashes by carefully draining the water. You can also use filtration.


Now I know there are traces of various metals in us, as well in flowers and trees. But how can ashes accumulate such a big amount of sodium? And how is the sodium bound into it. How does it turn into hydroxide?
There is sodium and potassium in wood.  When the wood burns some of the sodium and potassium become bound to oxygen.  The oxides become hydroxides when exposed to water.