Among the characteristics which make this collection such a rich potential resource for study are the presence of an amazing number of unique books and books of such great rarity that only a handful of copies is known. Virtually every book in the collection is in superb condition and many contain such special features as original drawings, artists' proofs, trial states, and laid-in letters. Mr Rosenwald's assemblage of books, plates, drawings, and engravings by William Blake is one of the finest ever brought together. Of the twenty illuminated books described in Geoffrey Keynes's Blake bibliography, the collection contains fourteen, as well as duplicates and extra plates. Finding that the Blake materials received more use than any other section of the collection, Mr. Rosenwald made copies of many of the illuminated books available to the Trianon Press for a series of facismiles.
Rarities are, however, but one aspect of the collection.
It particular importance arises from the quantity and unity of the material. The collection catalog describes Mr. Rosenwald's gifts to the Library of Congress in the years 1943 to 1975. Accounts of subsequent additions can be found in the division's acquisitions report of the Quarterly Journal. During Mr. Rosenwald's lifetime the collection was housed in his private gallery, the Alverthorpe Gallery in Jenkintown, Pennsylvania. The division houses a card catalog containing author entries for the books and manuscripts in the collection.