In a fit of either temperament or sanity, many artists decide to paint or plaster over their own work to make way for something better. Art historians call this "over-painting." And for years, researchers have wanted a way to peek underneath the over-paint to see what came before the final product. Sometimes these hidden drafts let us see what came before a classic work of art, and sometimes they reveal something entirely unexpected. And terahertz radiation is the revolutionary discovery that makes it possible to go beneath the over-painting.
Terahertz radiation was recently used on a painting under restoration in the Uffizi Gallery in Florence. Giotto's Polittico di Badia, was painted in the 1300s, so anyone examining it had to take the utmost care. Terahertz imaging revealed that it was painted on fabric laid over wood, typical of the painting techniques of the time, that Giotto used lead paint to make the white parts stand out, and that the painting was absolutely lousy with gold. The painting if of a solemn angel, rendered in umber, surrounded by a golden halo and golden wings, and wearing a golden robe. Gold foil was used under paints to make the painting radiate heavenly light.
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