He knew that people do not use vellum to write on anymore.

他知道人们已不再用羊皮纸写字。

He saw pieces of vellum, animal skin that people wrote on in the past.

他看到了多张羊皮纸，这是过去人们用来写字的兽皮。

But once I'd started looking at Leonardo and vellum, which is basically parchment.

但当我开始看达芬奇和皮纸的联系时，皮纸一般都是羊皮纸。

We've got no drawings about Leonardo on vellum on animal skin.

我们以前没有发现达芬奇用皮纸画的画。

I think the point about it being vellum is really interesting.

我觉得关于皮纸这点很有趣。

And once you're thinking about vellum and coloured chalks on vellum all of this falls into place.

一旦你想到皮纸和在皮纸上用染色粉笔画，这些内容都说得通了。

Now this was executed on vellum I understand, so that's something usually used in codex or a book production.

我知道这幅画是画在皮纸上的，这种材质通常是用于古抄本或者书。

Instead of paper, European books were handwritten on vellum or parchment.

欧洲书籍不是纸质的， 而是手写在牛皮纸或羊皮纸上的。

The other aspect is you think well why would he do it on vellum?

另一方面你会想为什么他要画在皮纸上？

He replaced the precious work, and his eye fell on a stout volume bound in vellum.

他换掉了这本珍贵的作品，他的目光落在了一本用牛皮纸装订的厚实的书上。