It is this tannin which makes leather durable and soft.

鞣酸让更加柔软，更耐用。

The water draws out of this bark a substance known as tannin; and the tannin changes the soft, jelly-like skins into tough, strong leather.

在水的作用下, 够分泌一种名叫鞣酸的物质, 而它就可以凝胶一般柔软的毛变成结实、牢固的。

It takes years for a skeleton to vanish, but the shoes treated with tannic acid—they won't eat them.

骸骨需要几年才消失，但是用鞣酸处理过的鞋子——海水无法吞噬它们。

During the summer the bark is peeled from the trees and taken to factories where the tannin is taken out.

在夏天，我们会从上削，之后进入工厂提取鞣酸。

Turns out, it was made from the tannic acid of gall nuts.

原来，它是用没食子（五倍子）中的鞣酸制成的。