The book of secrets
This book is made from copper. It is currently in a private collection in Sweden and is presumed to have originated in Sweden. Methods for making copper foil were known by the mid 1800's, and were exploited by Tiffany & Co as a replacement for lead to make exquisite stained-glass works. This led to suggestions that the dates from mid-to-late 19th Century. However, this has been disputed.
At first sight each page appears to be blank, covered in a mottled patina. However, it is alleged that the book is in fact written in a way that cannot be seen easily or understood by those who do not know how to. The patina patterns on each page were made deliberately by the book's author, and so represent a formidable cryptographic challenge to decode. It is believed that the book records recipes and processes that the creator developed in their quest to give copper life-like properties. It also reputedly contains a prophecy of a date and place where the greatest alchemist of all, the apocryphal 'Elijah (or Ellah) Artista', will reveal themselves to the world and "make life spring forth of metals".