These are paste papers from an early 20th-century edition of the German translation of Le déserteur, an opéra comique by the French composer Pierre-Alexandre Monsigny. Book from the collection of Leon Laserson.
These two volumes were standing out among other tomes at the book market in the Hague. But what most impressed me wasn't visible while the volumes were tucked between other books. Just check the marbled paper!
Just a couple of weeks ago I saw a post from Simon Beattie about an 18th-century Russian book with "marbled" endpapers that were in reality hand-printed. Imagine my surprise when I found something similar just a few days later!
Among other exciting things, I found in the last volume of the Dutch Printers Yearbook from 1911, was an article by Reinier Willem Petrus de Vries Jr. about a technique that "recently" attracted the attention of some bookbinders — starch marbling.
The book is another find at the book market in the Hague. The Life of Willem III (Het Leven van Willem III) by Frans Bührmann was published in Amsterdam in 1874. But I'm not sure whether the endpapers come from the same time.