Italian Gesso 1kg

This dry ground natural gypsum (calcium sulfate) is made according to an old process near Siena, Italy. Gesso Oro per Indoratori is quarried and processed in Colle Val d'Elsa, the birth place of Cennino Cennini, in the same locale where he obtained his gesso for "gesso sottile." Gesso (Italian for gypsum) was used since before the Renaissance and mixed with glue size to prepare wood panels and frames for painting and to adhere gold leaf.

Softer than chalk (3 Mohs scale of mineral hardness), its hardness of 1.5 to 2 makes a soft white gesso that is easier to polish to a smooth finish for gilding bases and painting grounds. Calcite or chalk, being a carbonate, effervesces on exposure to acids, whereas gypsum alabaster, when so treated, remains practically unaffected.

Recommended in Cennino Cennini's treatise on painting, Il libro dell'arte (often translated as The Craftsman's Handbook), to make "gesso sottile" for painting grounds. It makes a brilliant white gesso that can take a high polish for gilding. Add to oil colors and mediums as a transparent filler and to give body or in tempera as a white filler.