I would like to point to this wonderful sculpture book once more.
Specifically, see Chapter 4: "Plaster of Paris" through "Cleaning Old Casts" on pages 57-72. Also see "Storing Plaster" on pages 88-89.
The Materials and Methods of Sculpture.
Jack C. Rich.
NY: Dover Publications, 1988.
Notes: Reprint. Originally published: New York : Oxford University Press, 1947. Includes index.
Description: xxi, 416 p.,  p. of plates : ill. ; 24 cm.
This work is licensed under a Creative Commons Attribution-ShareAlike 3.0 Unported License.