A little while ago I had the opportunity to attend a lecture on 3D modelling of Van Gogh’s Sunflowers hanging in the Van Gogh Museum in Amsterdam. This was part of the University of Queensland World Science fair, with a guest speaker Emeritus Professor John Drennan, specialising in electron microscope and conservation work of some of the world’s most famous paintings.
This ‘mega’ microscope works by firing a beam of electrons to create an image of the specimen. It is currently used in examinations of medical biopsy samples, molecular and crystalline structures, forensic samples, fabrication of silicon chips. But electron microscope can also be used by art conservationists to examining the characteristics of various surfaces.
The Industrial revolution of the late 19th century saw new possibilities in pigment sources and paint colours available to artists. Synthetic pigments could be utilised, and artists could achieve colours and their combinations previously not possible. (Something that made Impressionists very excited!) One particular change that was happening is the use of zinc oxide instead of lead in oil paints. Unfortunately for the artist, over time zinc oxide reacts with oil to make tiny bubbles appear on the surface of the painting. Naturally, this is making conservationists very nervous in the museums around the world! Imagine a painting of a beautiful girl praised for her glowing skin – only to find her covered in what looks like pimples 70, 80, 100 years later! (An issue identified in Frederic Leighton’s Winding The Skein at Art Gallery of New South Wales.) Certainly a nightmare for any guardian of precious art of the past centuries!
Van Gogh is an artist of depth, guts and a certain je ne sais quoi – an artistic charisma if you like. He worked profusely over only about a decade to leave behind almost unbelievable amount of work. Van Gogh loooooved sunflowers. In fact, he made seven paintings of sunflowers! (One of them was destroyed in the bombing of Tokyo, so only six remain today.) Chemically speaking, the specific challenges with Sunflowers come from the varnish that was applied to the painting after Van Gogh’s sister-in-law (to whom his paintings were entrusted) died. Varnish, meant to protect the painting, can also discolour it, reducing the artist’s intent of colour and vibrancy. Attempting to remove the varnish (or ‘clean’ the painting) requires application of a solvent to the painting’s surface. When dealing with rare and hugely expensive artworks, it’s a major operation!
So what can we achieve with the electron microscope? The conservationists collect flecks of paint that fall off the surface of the painting, or take a spec of paint at the edge, and then place them under the microscope. As electron microscope is capable of magnifying the image 8,000,000 times, only a tiny spec of paint is needed, and no painting surface is damaged in the process. The powerful technology is able to then slice the specimen into layers of about 200 molecules thick and recreate a 3-dimensional image of the sample. Gives a whole new meaning to the phrase “break it down”, doesn’t it?
The main issue with Sunflowers is porosity – very small (microscopic 😉 ) holes in the painting. The researchers and the conservationists wanted to know how big these holes are and how far they extend to avoid letting the solvent go through the varnish into the painting itself. In fact, when you begin to look into the chemistry of paints and other substances coming in contact with them – it’s mind boggling! 
For instance, chrome in paints goes yellow over time. Changes can happen in canvases themselves. If a painting is waxed for stability at the back of the canvas, that wax can move through the painting, reacting with the varnish! At a recent exhibition of “The Greats” at Art Gallery of New South Wales, I saw a beautiful 18th century portrait of a girl grieving the loss of her pet bird: Jean-Baptiste Greuze’s Girl with a Dead Canary (1765). The painting originally showed a yellow bird lying on green branches. Now it’s a white bird on blue branches! The painting is touching, but the blue twigs can mess with your head.
The point is that the chemistry is very much alive in these artworks. Who knows what other problems are hiding there that may not have surfaced yet? Art is not ‘immortal’, and the race to preserve them allows us to keep hold of the connections to our past. When you walk through the streets of Rome and step on the stones that have born the weight of soldiers, emperors and slaves – doesn’t that give you goosebumps? That human connection to our past is the reason people dedicate their lives to preserving objects, dwellings, and paintings of those that shape the culture of our world, somehow mutating into a part of our identity.
The aim of projects like Professor Drennan’s is to understand the chemistry of the painted canvas, and, if possible, to slow or even stop the changes. Of course there are methodological challenges here. Firstly, how representative is the sample of paint from the edge of the canvas? We are assuming that the artist takes the same care and fastidiousness when preparing the edge as he does working on the centre of the canvas. That’s a fairly loose assumption. Secondly, the artist can change the type of paint, canvas, and other ‘chemistry’ that ends up in his work. How many artists really paint with longevity in mind? From my experience they want to be acknowledged NOW, and preserving the work for someone 300 years from now is a distant thought. But for us as viewer of today, the retrospective look at the great masters gives us a sense of self and inspires us in so many ways.
Another interesting point raised by the professor was the tension between connoisseurs and conservationists. As technologists, conservationists have to focus on scientific methods to fight against the damage of time, oxygen, light, and chemical reactions that slowly eat away precious art. On the other hand, connoisseurs have made careers on examining brushstrokes, stylistic elements, and making comparisons with other works in the artist’s canon. Indeed, there are limitations with every method. While traditional connoisseurship offers a subjective analysis, the use of electronic microscope is limited by its expense, availability and the access to the artworks’ samples. I would love to see them working together to save, expand knowledge and inspire.