How many different materials can you burn to make black pigments? What does the most important white pigment in Western art have to do with horse poop? It’s all there in black and white.
Lead in the Girl
Just like x-rays of the human body, x-rays of paintings show differences in absorption of the radiation by different materials. The differences depend on the thickness of the materials, and the atomic weight of the elements in them. Lead white appears white on an x-ray because it is ‘heavy’: i.e. it has a high atomic weight.
Since lead white is a component of the ground, the x-ray shows marks where the ground was spread over the canvas using a knife.
Paint that contains a lot of lead white are also x-ray opaque: her eyes, the highlight on the pearl, her shirt, the highlights in her headscarf, and the left side of her face. The Girl’s face contains a lot of lead white where she faces the light. This creates a strong contrast between the lit and shadow areas, which reinforces its 3-dimensionality.
As black as she is painted
Vermeer seems to have used two different black pigments: charcoal and bone black. Sometimes he mixed them together. Perhaps he was trying to achieve a specific colour. Charcoal produces a bluish black, whereas bone black is brownish. The black pigments that Vermeer used in the Girl are mostly hidden beneath the surface, or mixed with other colours. As you’ll find out in a blog in a couple of days, the background of the Girl wasn’t originally meant to be black.
Charcoal is made by charring wood (usually willow or grape vines) inside a closed vessel in a fire. A charcoal stick can be used for drawing, but can also be crushed and mixed with a binding medium to make ink or paint.
[fig. 12e: sample 21 with charcoal]
This cross-section is from the background of the Girl, where Vermeer applied charcoal black as an underlayer beneath a translucent glaze. The splintery black particles are the charred wood fibres.
The other black pigment that Vermeer used was bone black. What is it made from? Bones, of course…but also animal horns or ivory. Because bones are mostly made of calcium phosphate, the elements calcium (Ca) and phosphorus (P) can be detected with the scientific techniques SEM/EDX and FIB-TEM. These particles are also usually rounder and smaller than charcoal splinters.
Vermeer used a mixture of charcoal and bone black in the underlayers beneath the clothing (which I’ll discuss in a later blog post).
