I’m not convinced regarding varnishing. I feel that it destroys the beautiful matte texture of egg tempera on gesso. I have yet to be happy with a varnish, and resist doing it to the very last moment … if ever. So why varnish? Usually to protect the painting from dirt and dust, and to even out the differing eggy glossy and watery matte finishes. Varnish is just a film over the top, and should be removed and replaced every 30 years or so anyway – presumably by very busy expert restorers. Yet egg tempera paintings have lasted the distance since before the Renaissance, and restorers believe they were probably never varnished. Egg tempera painter Altoon Sultan writes in her book, The Luminous Brush, that a conservator at the Metropolitan Museum of Art in New York told her that varnishing egg tempera paintings is not necessary – he recommended burnishing! Rubbing the surface of the paint with an agate stone, or a soft cloth increases the sheen, as per gilding, and makes it more water resistant. I experimented with this on one or two older paintings which are well and truly ‘cured’ (this can take 8-12 months).
Results are impressive. I’m convinced – I will never varnish again! It is also illuminating about how successfully I managed to ‘temper’ the pigments with the egg mixture, as any raised surfaces and chunky bits not mixed correctly tend to create issues and drop off!
It just takes more time… but this goes hand in hand with all things tempera. But the sheen, the final patina of the surface is just truly beautiful, and worth the effort.