..more about the book in Rembrandt's painting 'The Syndics'

..the nice thing of research is that we find out more and more....
Benjamin Binstock writes in 'Seeing Representations; or, The Hidden Masters in Rembrandt 's 'Syndics' (Representations Vol.83. No 1, pp 1-37, Summer 2003) an extensive explication about the book in the painting being an account book.
The Guardian refers to this in a book review as a 'stunning insight' https://www.theguardian.com/books/2007/jun/23/art
Jérôme Sans talks about 'The Syndics' in 'Rijks, Masters of the Golden Age' by Marcel Wanders.
He mentiones that the book on the painting is a swatch book, a sample book.
It is not only me who thinks that  makes sense !