Historical Painting Techniques, Materials, and Studio Practice

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Figure 2. Fourier traniform irifrared spectra of gypsum bumed at 500 ° C: (a) anhydrite sample before
treatment with water; (b) slurred in water for two days, the sample still consists of anhydrite; (c) slurred
with water for ten days, the sample now consists of dihydrite.
kind of oven had been in use in the Mediterranean civilizations since early
Roman times (19). The painter's manual of Mount Athos actually describes
the baking of gypsum in a similar type of kiln (20). This manual suggests that
the product from the burning process would be soluble anhydrite, which,
soaked in water, would form the dihydrate product again.
In Cennini's directions for the preparation of the gesso sottile, the burnt
gypsum should be soaked in water for about a month. Lindberg states that
Thompson's translation of the word rinuoua as "stir up," referring to stirring
the water every day, is not correct. Thompson may have mistaken the "n"
for "m" (21). Rinuoua literally means renew or change. Lindberg further
argues that siinarsiscie means "to dry," dismissing Thompson's translation of
"rots away" as incorrect. Lindberg offers the following interpretation: the
water should be poured off the soaked gesso every day until the gesso is
almost dry, which simply means that as much water as possible should be
Federspiel 61