.. The strange scroll

Check the bookshelf. ( Pick up the book of secrets. )

Yes, the Book of secrets says:
Aracane ink is totally invisible except to the eyes of very powerful druids. However, a handful of ashes mixed with an ordinary ink will cause the arcane ink to come forth.

Maybe you could follow that instruction. You should have black ink in your inventory.
Combine the black ink with ashes ( From the bookshelf. Pick some ashes from the urn. ) to reveal the secret in the scroll.

This scroll must tell you how to get into the chest.

The lock of the chest is a face. The scroll will tell you what to put in what socket.