On the fiftieth day, Lin Yu'an got up early and started preparing the tanning solution.
Soon, after most of the tree bark had been processed into small fragments of various sizes, Lin Yu'an took out the largest ceramic pot he had previously made.
Lin Yu'an layered these processed bark fragments into the ceramic pot, using a thick wooden stick to tamp them down occasionally, filling the pot to the brim.
"Extracting tannic acid, the more finely the bark is processed, the greater the contact area with water, and the higher the extraction efficiency of tannins."
"Then comes the long simmering process."
He moved the heavy ceramic pot to the mouth of the furnace and added enough hardwood kindling to the combustion chamber below.
"I need to boil as much tannic acid out of the bark into the water as possible, forming a concentrated tanning solution."
"This process usually requires several hours, during which the water must remain boiling."
