The Girl’s pearl earring isn’t the only part of the painting that looks like it is semi- translucent, as if you can almost see right through it. In traditional painting technique, artists applied thin translucent glazes over opaque underlayers to modify their colour. The underlayers have good covering power, and reflect light. The glazes on top contain pigments that are translucent in oil, so light passes through them.
Background
When Vermeer painted the background, it had a smooth, translucent green surface that was glossy like enamel. Over time, the dyes have faded and degraded, so some of this effect has been lost. Vermeer built the background up with two layers. First he applied a thin layer of charcoal black. Then when it was dry, he painted a deep translucent glaze on top. The colourants in this glaze – indigo (blue) and weld (yellow) are translucent in oil. The other components in the glaze – chalk, alum, lead white and a little red ochre – wouldn’t have done much to affect its clarity. Vermeer’s glaze is thicker than the varnish (which was applied during the 1994 treatment).
Blue headscarf
Yesterday you learned about ultramarine, the blue pigment that Vermeer used in the Girl’s headscarf. He painted the left side of her head in light blue layer to show where it faces the light. The right side in shadow is a darker blue applied on top of a dark underlayer. To unite the two sides and to give extra intensity, Vermeer applied a blue glaze in a zigzag shape over parts of both.
The ultramarine-containing glaze is transparent to the naked eye, and also transparent to infrared. This means that it seems to ‘disappear’ when we examine the painting with infrared reflectography and near-infrared imaging.
Varnish
Optical Coherence Tomography (OCT) didn’t only reveal the original glazes in the ‘virtual cross-section’. It also shows the varnish that conservators applied to the surface of the painting during the treatment in 1994. An isolating varnish was brushed on before the conservators filled and retouched the damages. It saturated the colours of the original paint. It also separated the original materials from the restoration materials, which would make it possible to remove any retouching in the future. At the end of the treatment, the painting was given a final varnish.
Varnish is applied to paintings to saturate the colours and protect the surface. Think of a pebble on a beach. When you pick it up out of the water, the colours are bright and saturated because the stone is wet. When it dries out, the surface is rough and the colours are dull and matte. The varnish on a painting is like water on a pebble.
Unfortunately, varnish layers often become yellow and brittle over the course of time and when exposed to UV rays. This is the reason why paintings are ‘cleaned’. Conservators remove old yellowed layers, and it is almost always varnish previously applied by other restorers. Nowadays we slow down the yellowing process by protecting paintings behind UV-filtering glass, and by choosing varnishes that do not change colour anywhere near as quickly as the ones used in the past.
