Casing is a term to describe the moistening of leather prior to working it.
Vegetable tanned leathers become pliable when moistened. They can then be shaped, cut, or stamped more easily than when dry. As the leather dries out it retains the shapes that have been worked on it.
Chrome tanned leathers are less accommodating to these processes, even when cased, although that tanning process does make them more flexible.
The amount of wetting required for successful casing depends on a great many factors. Advice tends to vary from "sponge some water over the surface and wait a few minutes" to "immerse in water for a few moments, drain, and leave in a plastic bag for an hour". Experience, water, and patience seem to be the main requirements ~ quantities depend on the type and thickness of the leather, the work to be done, and the experience of the craftsperson.
Suitable leathers can, with skill and technique, be moulded to fairly complex shapes such as face masks, or carved with simple or complex outlines. These may be combined with patterned stamping and staining to provide decoration.
Casing is also the term used for describing the covers of case-bound books [122932] (Books made with a separate book blocks and covers.)
