Monday 26 August 2013

Hello from the Getty Conservation Institute – What paint is this?

When we talk about modern paints, we are referring to those based on synthetic media that were developed during the 20th century. For example, the binder in oil paints is made from natural vegetable oils, often linseed oil derived from flaxseed, whereas an acrylic paint is made from synthetic polymers manufactured from petrochemicals.

We generally rely on the artist’s description and close examination to get some idea of what paint it is. But the artist may not remember what paint they used, visual appearance can be inconclusive, and even if we did know what product they had used, the manufacturer is unlikely to reveal everything about it because of commercial sensitivities. So for an accurate assessment, it is necessary to do chemical or spectral analysis.

GCI Assistant Scientist, Herant Khanjian, with the FTIR microscope. The results from the analysis are on the computer screens behind 

While I have been at the Getty, we have been completing the analysis of some samples taken from paintings in the Modern Paints Aotearoa exhibition. The first we looked at were some tiny black scrapings that were taken from Stalagmites – Stalactites, 1964 by Theo Schoon. They are so small that you cannot see where they came from on the painting with the naked eye.

Image credit: Theo Schoon, Stalagmites - Stalactites 1964, oil on board, Auckland Art Gallery Toi o Tāmaki, purchased 1989 

GCI Assistant Scientist, Herant Khanjian placed a piece of the sample on a tiny ‘diamond window’ (a hard transparent platform) where it was flattened with a very small metal roller. The sample was then placed under the objective of the FTIR (Fourier transform infrared spectroscopy) microscope.

 The image of the sample on the diamond platform is projected on the front of the microscope 

FTIR uses the infrared radiation to analyse and produce information in the form of a spectrum (or chart) that is characteristic of the sample components. In the spectrum are bands which represent chemical bonding between two particular atoms or group of atoms in a molecule. The information is compared with spectra of other known material for identification. The results were a little confusing so we also did a solvent extraction. This means that a solvent was dropped on the sample to draw out the organic components which were analysed. The results were a lot clearer this time, and it appears that the paint is oil and alkyd.

You can find out more about Herant Khanjian here:

- Sarah Hillary, Principal Conservator

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