The science of making colour

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The latest digital imaging techniques are literally shedding new light on the ingenious variety of materials that have been used over the centuries to create artists’ paint pigments.

A new exhibition at the National Gallery in London is looking at the history of colour making over time.

Preparations for the exhibition have been given a helping hand with a state-of the art positioning easel that gives the ability to examine great works of art in unprecedented detail.

The easel was provided through the support of the Engineering and Physical Sciences Research Council.

Find out more about the easel and how it is helping conservation work at the National Gallery.

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Ashok Roy - Director of Collections at the National Gallery [AR]

This is the first time any gallery or museum has put on such a comprehensive exhibition on the materials of colour in painting and we've been able to do it because we have such a long history of study of the Collection as well as a very well-equipped scientific laboratory to analyse the paintings that are at the National Gallery.


Today artists are spoilt for choice by the vast array of synthetically manufactured paint colours available for them to work with. But journey back in time and you'll find that the things used to make pigments were often as creative as the great works of art they contributed to, from minerals that contain lead, mercury and copper, to crushed insects and sparkling gemstones.

It's a story that brings together artistic and scientific endeavour and it's being celebrated at the National Gallery in the first exhibition of its kind in the UK. Called 'Making Colour', it spans hundreds of years, from the Middle Ages to the end of the nineteenth century. Ashok Roy is the Director of Collections at the National Gallery.


We have always worked in what you might call a multidisciplinary or cross-disciplinary way. In the National Gallery, we have a long tradition of scientists working with conservators and with art historians and, of course, we bring different skills and different knowledge to understanding the Collection. We've reached that point where we really know a great deal about the way in which European paintings were made and that means the materials that we used to create them, the way those materials behave, something of their technological history, the connections between colouring materials used in painting and what we would call the sister arts of ceramics, glass-making, textile-dying and so on.


The exhibition has been given a helping hand by a recent addition to the National Gallery's pool of equipment. It's a state-of-the-art computer controlled micro-positioning easel. Around six metres long, it's capable of holding and slowly moving around a painting up to 2.8 metres high and wide. It was provided through the support of the Engineering and Physical Sciences Research Council. Their partnership with the National Gallery began in 2010. Joseph Padfield is a conservation scientist at the National Gallery.

Joseph Padfield - Conservation Scientist at the National Gallery [JP]

We use a number of different types of imaging techniques from visible light to infrared, to X-rays to ultra violet light and a number of different textual imaging processes. We decided that it would be easier to move the painting, rather than the camera, because that allows us to put any type of camera in front of the painting. The ones we're hoping to do in the future is one called hyper spectral imaging, where, instead of just taking a normal red, green, blue image of a painting, you actually measure all of the reflected light coming back, the whole accurate colour. So, if you're looking at different types of pigments, you can start to look at the reflected spectrum of these different materials and you might be able to look at doing pigment maps, for instance. Therefore, you can take a picture of the painting and map where different materials have been used, which is an area of on-going research. This is not something you can easily do now, but it's something that people are wanting to be able to do and are looking to do. So it is an area of research that we're hoping to get into in the future and this easel will give us a platform on which to begin.


One of the paintings being featured in the exhibition is Sassoferrato’s The Virgin in Prayer. Dated between 1640 and 1650 it shows the gentle serenity of Mary’s features as she holds her hands together in worship. The soft drape of her cloak is painted in a rich, spectacular, deep royal blue. The folds of the fabric are so convincing that you feel you could reach out and touch them. Ashok Roy describes how this pigment was created.


Sassoferrato's Virgin in Prayer is a very interesting example of the most spectacular use of a pigment called natural ultramarine. This was extracted from a semi-precious stone called lapis lazuli. Before the nineteenth century there was only one known source of lapis lazuli in the world and that's in what’s now a part of Afghanistan, a province called Badakhshan. From famous mines there, lapis lazuli was imported into Europe, and a good deal of it found its way into the manufacture of ultramarine pigment, which was a very precious and marvellous material. In this picture, a seventeenth century painter exploits its absolutely stunning pure blue colour, royal blue colour, in oil paint, which holds up over time extremely well. It's a very stable material as well as being such a pure wonderful blue colour, a precious material and a very beautiful material.


Joseph Padfield says the new easel will not only enhance understanding of how a painting like this is constructed it will also make the detailed examination of great works of art available to a much wider audience because of the images it will help to produce.


Look at it from any distance, you will see one blue, but if you're able to look at it closely, you'll probably see a lot more subtlety to it. You will see the different brushstrokes that will form the shadows and the highlights on the cloak/and allow you to see the detail of how the fabric has been portrayed, how the brushstrokes have been layered one over the top of the other, to see how the modelling has been achieved. You can only do that if you have the very special ability to actually take the painting down and look at it under a microscope, which is only really reserved for a very few people. But if you're able to put that type of painting in a system that'll allow you to get extremely high resolution images of it, it will allow that special experience to be achieved by many people.


The National Gallery's new state-of-the-art easel has also helped inspire another part of the 'Making Colour' exhibition which gives visitors the chance to get involved in an interactive experiment that will feed into future research on human colour perception. It involves capturing the responses of people as they view a picture under different conditions, using a tunable LED light source. So if you want to get a new perspective on an old master, then this unique exhibition is the ideal opportunity to do so. 'Making Colour' is on at the National Gallery until the 7th of September [2014].