This series of six books all written by Hartwell James is quite collectible because the illustrations were drawn by John R. Neill. Neill illustrated quite a few Altemus books but is clearly famous for the illustrations he did for the early Oz books. The Enchanted Castle has 40 Neill drawings. The cover however appears to have been done by the Decorative Designer firm.

Each title in this series has a unique book cover (http://henryaltemus.com/series/series84.htm). The covers of any one title however can be found with different colors and gilt. This book is an example. The new book being added to the database today has gold gilt on the cover in places where the other book shown here has red ink. Other color differences can be seen. I believe that the “gold gilt” book is the older book based on Altemus patterns but I cannot be sure since the interior of the books are identical.