The book describes the concept of invisible inks that are used by nobles, merchants, spies, etc. to conceal a content or to prove an authenticity of a letter or scroll.

Associated QuestEdit

Journal entry Edit

Invisible ink
Those wishing to conceal the true contents of their missives from third parties often resort to penning their letters with invisible ink. A message set down in this manner becomes visible only when the document is treated with a substance that reveals the writing.
Some use invisible ink as a dye, soaking entire pages in it instead of using it to write. The recipient of a message thus treated can confirm its authenticity by applying a substance that will turn the page a specific color, usually blue.