Maddeningly Faded: Paint & Conservation

Featured String: Why’s That Robe Pink?

Featured String: The Story of Colour

Moving around paintings from the Renaissance and earlier, it’s often possible to see surprisingly rosy pink robes, or saints whose bloody executions don’t appear to have shed any blood. This is hardly down to the squeamishness of painters! Not only were Medieval and Renaissance painters well used to scenes of suffering and bloody death, living in a time when the death penalty was a public spectacle, but from the 13th Century onwards the Franciscan movement directly encouraged the lengthy contemplation of the suffering of Christ (and the saints) as a way of becoming better people. Painting, in a society that was still largely pre-literate, was a big part of communicating this.

So why aren’t these paintings showing up in their full bloody glory?

It’s down to paint. One specific type of paint.

Madder Lake is made from the madder plant, a relative of coffee. Extracts from the plant’s roots, treated in the right way, produce both pigment and dyes used for making beautifully vivid red cloth and paint. The compound responsible for this red is called alizarin, and has since been synthesised.

Painting people wearing clothes dyed with madder using paint made from madder is just common sense. It means the colour is an exact match! It also produced beautiful glazes, which meant it was a go-to for artists who wanted their work to appear to its best advantage.

The amount that madder and other red lake pigments fade in contact with light depends a lot on what other paints it’s mixed with, because of their different chemical compositions.

Why does it fade? The short answer is “chemistry”. Dyes and pigments work by absorbing certain wavelengths of light and reflecting or transmitting the rest. The colour you see is whichever light wavelength is transmitted. Absorbing light takes energy, and sometimes that energy can cause a chemical reaction, which changes the structure of the stuff the dye or paint is made from. Once the structure of the pigment molecules changes, it reflects different wavelengths of light.

How likely this kind of destructive chemistry is depends on the nature of the pigment–what it’s made from. The ones that occur in nature, like madder, are more likely to to lose their colour. Red paint can often degrade faster because it absorbs higher energy (shorter wavelength) light. The more energy that is available, the more likely it is that those chemical reactions will happen.

madder.jpg

Credit: Daniela R. Leonard, An Exercise in Fugitivity: Investigating the fading of red lake pigments, e-conservation Journal 5, 2017

Where do colours come from?

Before people began to understand things about chemistry and colours and how they worked, we had to rely on what we saw in the natural world, instead of making our own colours.

That meant using minerals, like lapis lazuli and lead, which could be expensive to get hold of (lapis lazuli came from Egypt and Afghanistan and was expense to ship to Northern Europe!), or poisonous–many women became sick from using white lead paint on their faces as part of their make-up routine. Other natural mineral dyes like vermilion (made from the mineral cinnabar) or smalt (made from cobalt) degraded badly over time or in exposure to natural light, just like madder. Vermilion gets darker, and smalt loses its bright blue hue.

Plants provided dyes and pigments too, like indigo, weld (yellow), and madder. Even animals, like the Murex shells used to make Tyrian purple–one of the reasons purple was associated with Emperors was because it was so expensive to make a purple dye! Carmine red, too, traditionally came from the shells of tiny insects.

So natural pigments were often expensive, unstable, and unsafe! That’s a lot of incentive to come up with synthetic ones.

The first synthetic pigment was Prussian Blue, “possibly” invented in the 1770s by a German paint maker named Diesbach–by accident. A happy accident, as the pigment, as well as being much cheaper than lapis lazuli, can also be used to treat heavy metal poisoning.

The first synthetic dye, which also replaced a far more expensive source, was also discovered by accident! 18-year-old lab assistant William Henry Perkin was trying to synthesise quinine, a substance used for treating malaria, and instead created a vivid purple dye.

It’s not just the pigments

Making paint doesn’t just involve pigment. To get it to stick to the surface and move smoothly around instead of just being a dry powder, it needs to be suspended in a fat-based substance. Traditionally that’s been either egg, or oil. But what’s the difference?

Egg tempera paint is usually made from pigment powder and egg yolk, which is very fatty, and is used as a binder (fat binds things together), and some kind of agent, usually an alcohol or acid (wine or vinegar). Until the Renaissance, it was the main paint used in works of art.

Egg tempera has a flat, glossy, translucent finish, and it dries really quickly. It can be layered up easily because of that, like modern watercolours can, and used to create very delicate colour transitions. Andrea Mantegna used this type of paint.

The downsides of tempera are that egg isn’t a very waterproof binder, which means that works made from it had to be kept where they would be dry or risk being washed away. That does mean tempera paintings were also less likely to get faded by exposure to light! The other problem is that tempera is a very brittle paint, and unless it’s used on board instead of canvas, cracks will appear and chunks will flake off, spoiling the picture.

Because it isn’t waterproof, tempera paintings were often varnished to preserve them… causing other problems, like darkening the original colours, with otherwise would have been perfectly stable over time on the basis of their binder, although not necessarily their pigment.

What about oil paints?

Oil paints are made with pigment powder and oil, usually linseed oil, which can be diluted and made less thick with turpentine or other solvents. Although they’ve been in use in Europe since the 12th century, they didn’t really become popular until the Renaissance–around 1500CE.

Oil paints are thick and the thicker a coat is the longer it takes to dry. This means that artists could blend and mix their paints on the painting, and had longer to correct mistakes or create specific colours. Compared to the flat, precise colours of tempera, artists who used oils–like Mantegna’s friend and contemporary Bellini, could create more nuanced, lifelike images.

Oils are also more flexible, which means that they can be painted onto canvas, instead of flat boards, and they’re waterproof–in fact, some of the earliest uses of oil paints were to waterproof and colour fishing equipment!

There are downsides to oils too, however. While the binder in tempera is stable, oil paints by their nature get darker, yellower, and more transparent as they age–so the oil painting you look at isn’t the one that was painted 500 years ago!

Varnishing paint

Until the 19th Century, applying varnish to the finished painting–whether it was made with oils or with tempera–was what was normal. Because varnish is so thin, and traditionally made from natural substances (tree resin or shellac), it’s very vulnerable, and even if the paint behind it is okay, the varnish can discolour, or crack and flake, effecting the way the painting looks. However, these natural substances make paintings brighter initially than modern, synthetic varnishes can.

Because varnishes discolour over time, conservators have to remove and replace them if a painting is to stay looking as close to the way it did originally as it can!

How to stop or reverse degradation of paintings and…

Conserving works of art is a big part of the job of a gallery. The National Gallery not only restores and maintains conditions for the paintings in its collection, but also analyses them using X-rays and other techniques to see what previous versions lie under the surface canvas and what specific paint pigments were used. This can teach people lots both about how the artist worked and how to protect the paintings from degrading any further.

They also take care of the frames and supports of the paintings, which help to keep them looking their best!

Conservators at English Heritage go into depth about their process here:

As these art dealers note, past conservators have done things differently, sometimes painting over older paintings to make them look more in keeping with the fashions of the time. Conservators don’t do that any more!

…how not to do that.

Seeing conservation of paintings broken down like that may make it look easy, but it’s painstaking work! Even professionals can get it wrong or be highly misleading.

We all remember this, after all:

fresco.jpg

Source: New York Times, 2012

It’s definitely better to leave the conservation of artworks to the professionals!

A little last word


I’ve talked about this before, but the story of pigments and colours is a great way to learn about the whole of history, using art as your way in:

Now I know, because of a placard on a painting that I saw at the V&A Museum some years before, that a lot of medieval paintings have “white” cloth because the cloth was originally painted red using a paint made from the plant madder, which because of its organic base and short wavelength of red pigment, is particularly susceptible to fading in natural light (one very good example of this is Raphael’s cartoon for The Miraculous Draught of Fishes)

also know, because I watched (several) BBC 4 series in the intervening period, that a lot of paints during the Renaissance underwent a change in composition of manufacture which continued all the way through the Victorian period (when dangerous green dyes made of arsenic manufactured from the mining waste […] were gradually replaced with safer new alternatives), and onward into the mid-twentieth century as synthetic pinks and purples were discovered. This information in this paragraph has been itself synthesised from three separate BBC documentaries (one about colour, one about dangers in the Victorian home, and one about the history of chemical discoveries), and the delightful William Morris Gallery in Walthamstow.

Mineral pigments, I learnt from one of those documentaries, are much more long-lasting, like the blue used in many of the Marian robes in the medieval paintings in the Sainsbury Wing: this blue is derived from Lapis Lazuli – available to view in its natural state in the Natural History Museum’s geology and mineralogy galleries, or in carved and jewellery form in the Egyptian galleries at the British Museum.

The process of colour creation continues to this day. In fact, there has been a recent and well-publicised art world spat about this, between hipster pigment creator Stuart Semple and celebrated British artist Anish Kapoor, whose arresting, often red-heavy work has been displayed and is still displayed at both the Tate Britain and the Tate Modern.

In this story of colour, answering a simple question about a bloodless St Sebastian painting in Room 57, I’ve taken you through knowledge collected by chance viewings of documentaries, and through the V&A Museum, the Natural History Museum, the Science Museum (where else would you go to learn about the chemical processes in making dyes and pigments?), the William Morris Gallery, the British Museums, and the Tates. I’ve taken you on a whirlwind tour of a good six hundred years of pigment history moving forwards, and could just as easily take you back through time to talk about the evolution of Madder – with a visit to Kew Gardens – or the historic uses of Lapus Lazuli and Cadmium, and how trade in mineral pigments helped develop connectivity in the ancient and modern world.

 

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