Scientists find glass painting secret

WASHINGTON -- How did paintings by Tintoretto and other Venetian Renaissance artists get their special glow?\nUsing an electron microscope, Barbara Berrie, senior conservation scientist at the National Gallery of Art, discovered one of their secrets: tiny bits of glass the artists mixed with their pigments.\n"By looking beyond the limits of their usual practice and transforming materials from other trades to their painting, the great artists of the Renaissance created a palette that gave them an immediate and lasting reputation as brilliant colorists," Berrie said.\nIt was long thought that Venetian painters, glassmakers and ceramic designers each had their own ways of concocting paints and dyes, probably getting the ingredients through apothecaries, as in most of Europe.\nBut Louisa Matthew, head of the Visual Arts Departments at Union College in Schenectady, N.Y., found evidence that Venice developed a special market for dyes and pigments a century before other European areas did.\nShe was poring through the Venetian archives for information on how local artists did business. Among the dusty wills and tax records, she came upon an inventory of 102 items drawn up after the death of shop owner Domenico de Gardignano. He is identified in Italian as "dai colori" -- "among the men in the color business."\n"There are certain pigments that contain glass mentioned in the 1534 inventory, but by no means all," Matthew said. "Because (customers) were all buying colorants in the same place, we hypothesize that they traded ideas and ingredients including materials not on the shelf."\nPeople from many different trades bought supplies at de Gardignano's shop and were likely to have shared both ideas and materials, Matthew surmised.\nThat possibility led to Berrie's examination of paint samples under an electronic microscope. She discovered rounded bits of powdered glass, only thousandths of an inch thick, in two paintings by Lorenzo Lotto -- one in a red gown worn by St. Catherine, another in an orange-red coat worn by Joseph in a Nativity scene.\nGlass was also discovered in a yellow pigment used in a Tintoretto painting of Jesus at the Sea of Galilee.\n"They're also teaching me a lesson: to try to go beyond the bounds of what I know and what I think is right," Berrie said. "It's a good trick for an old artist to teach a new scientist something"