Venetians Added Ground Glass to Renaissance Paints

In the current issue of "Science News", Barbara Berrie and Louisa Matthew, from the conservation department at the National Gallery of Art, report on new discoveries in the paint formulation of sixteenth century Venetian paintings. It seems that ground glass was added to the powdered pigments upon grinding in linseed oil to increase transparency and to speed the drying time of the paint. Microscopic traces of glass were found in samples of Lorenzo Lotto's pigments viewed by Berrie "using scanning electron microscopy, energy-dispersive spectrometry, among other sophisticated analytical techniques"

"Upon closer examination, Berrie found high-quality silica in a form routinely used by Venetian glassmakers. During the Renaissance, they obtained it from quartzite pebbles along the Ticino River in northern Italy. They would then grind the quartzite into a fine powder."


Lorenzo Lotto
detail: Allegory of Virtue and Vice, 1505, National Gallery of Art

"For the Venetians to be able to use this ultrapure source of silica was a real technological innovation. Traditionally, glass was made from sand, which is loaded with impurities such as iron. The iron gives glass a green tint. Using pure silica, helped Venetian glassmakers to create their colorless cristallo. Perhaps Lotto was trying to achieve the same clarity in his paintings. He was layering these paints so thinly, he must have been taking advantage of glass' optical properties, says Berrie."

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And I highly recommend the color histories found on:

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