gypsography

from The Century Dictionary.

• noun The art or practice of engraving, as inscriptions, upon natural gypsum in some one of its forms, as alabaster.
• noun The art or practice of engraving on casts of plaster of Paris.

from the GNU version of the Collaborative International Dictionary of English.

• noun The act or art of engraving on gypsum.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun The art or process of engraving on gypsum.