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Storing Leftover Gesso
It is common to prepare more gesso than can be used in a single session. While refrigerating leftover gesso for short periods is standard practice, gesso often spoils if not handled correctly.
When chilled, collagen glue naturally gels, turning liquid gesso into a firm, tofu-like mass. For short-term storage (several days to a few weeks), spray or pour a thin layer of alcohol over the surface of the gesso, seal the container, and place it in the refrigerator. Before reuse, pour off the alcohol and warm the gesso gently in a bain-marie until it returns to a liquid state.
Do not place a cold glass jar directly into hot water, as this may cause the glass to crack.
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Long-term storage method
(after Ksenia Pokrovsky)
Gesso spoils from the surface inward. To slow this process, a mild antiseptic can be used that does not interfere with the gesso’s structure or performance.
The recommended preservative is phenol (carbolic acid). It is commonly available at drugstores as an oral antiseptic spray (e.g., Chloraseptic), which contains approximately 1.4% phenol and is sold for sore throat relief. These sprays are tinted with food dyes (red or green); the dyes are not colorfast and dissipate quickly, and they do not affect the color of the gesso.
Alternatively, phenol may be purchased from Natural Pigments as a 4% carbolic acid solution. Either option is suitable.
Procedure
1. Scoop the gesso into manageable chunks.
2. Place the chunks on paper towels generously sprayed with phenol.
3. Spray the gesso pieces themselves with phenol.
4. Wrap the gesso securely in the treated paper towels.
5. Place the wrapped gesso in a sealable plastic bag.
6. Store the bag inside an airtight container.
Refrigerate the container. Do not freeze. Freezing permanently damages the binding properties of collagen glue and renders the gesso unusable.