Van Gogh – Underlying Paint and Research
What do x-rays and Infrared thermography reveal in a painting? Basically, all that exists within, and beneath the top layer of paint.
We are aware that Vincent painted over several of his paintings, and this was largely due to lack of funds. In fact, when the Van Gogh museum in Amsterdam X-rayed 130 of Vincent’s paintings – they determined that 15% of said works had been painted over.
Still life with two sunflowers (F 376 JH 1331) is painted over a portrait of a man wearing a straw hat. (Most likely a self-portrait).
Cottage at nightfall (‘La Chaumière’) (F 83 JH 777) Painted in Nuenen 1885
shows a shepherd with his flock underneath, as does Two baskets of potatoes (F 107 JH 933) also a Nuenen completed work in 1885. In fact, this painting additionally reveals a woman at the spinning wheel underneath.
Glass with Yellow Rose (F 218 JH II44) is painted over a plaster study… to name just a few.
Underlying paint (and nail holes) from the painting in question
It has been determined from sheer scrutiny using magnification, that the painting in question was created using several layers of paint. Of course, this is exactly how Van Gogh applied his oils.
He started with a white ground like Calcium carbonite white with little lead white as his first layer, and add a second layer of perhaps lead white and zinc white or other pigments. Zinc white yielded a higher impasto, though was also more susceptible to flaking.
When Vincent reused canvases, meaning he painted over existing paintings, he employed various methods of concealing the underlying painting. Sometimes he would scrape down the paint, or use a dark color blocking paint before applying fresh ground. Other times he would apply a combination of pigments directly on top to obscure the original, and more often, choice of pigment nearly always included emerald green.
Over the past decade, a number of studies have been carried out by chemists and scientists to determine the degradation and instability of the pigments cadmium yellow, chrome yellow, red lake, and other colors used by Van Gogh. Vincent used his favorite color yellow in many of his paintings, and would employ three different pigments; chrome yellow, yellow ocher, and cadmium yellow. Chrome yellow contained sulfate groups, and as such were susceptible to discoloration by turning a brownish green when exposed to light. We can see this occurring in the Sunflowers series, (and possibly the thatched roof of the painting in question).
By analyzing a selection of Vincent’s work using x-ray spectromicroscopy and related relevant methods, we now know that Van Gogh’s Irises which appear blue were once vibrant violet. The walls of Vincent’s “The Bedroom” were also violet though are now blue, and the floor now brown from pink. This is due to red lead turning white, and essentially appearing faded.
An international team of researchers led by Koen Janssens at the University of Antwerp identified Plumbonacrite (3 PbCO3∙Pb(OH)2∙PbO) as the missing chemical link responsible for the degradation of Red Lead.