Gesso is plaster, usually plaster of paris sometimes horsehair plaster, applied to a wood surface and carved in detail. It is often then gilded but sometimes finished with other applied finishes.
In some French furniture, the carving underlies the gesso and it is used to give a very smooth surface to allow gold leaf to be applied or to give a very high gloss finish without the difficulty of preparing a wood surface to the same level. Of course, you lose the wood grain when you apply gesso.
President, NAWCC Chapter 174
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