Miranda Hinkley (in the studio): Visitors to the Sainsbury Wing – the area of the Gallery devoted to the earliest works in the collection – are often struck by the ubiquitous use of one particular colour. Painting after painting glitters with gold, one of the most costly, prized, and difficult substances to work with in the history of art. To find out more, I spoke to Philip Ball, whose book, 'Bright Earth', explores how artists have used colour through the ages. We met in front of 'The Conversion of Saint Hubert' – a 15th-century work depicting the saint kneeling beneath a sky of gold – and I began by asking Philip how the extraordinary effect would have been created.
Philip Ball: It was generally applied as gold leaf, so very very thin gold foil. So people would take – they would actually take gold coins – they would literally take coinage, there was no law against doing that then and they would hammer them and flatten them out into sheets, and just keep hammering and hammering away until the gold was almost transparent it was so thin. It was really sort of gossamer thin. And in fact for gold leaf in the Middle Ages a typical thickness is something like only about 2,000 atoms of gold thick, so incredibly thin. So you could get from a single ducat, a florin, a gold coin in medieval Italy, you could typically get maybe 100 or 150 pieces of gold leaf measuring typically something like five to eight inches square.
Miranda Hinkley: So how is the gold leaf actually applied to the wooden panel?
Philip Ball: The panel was first of all prepared in several layers and before the gold was applied typically the painter would apply a red or reddish brown underlayer and part of the reason for that was that because the gold was so thin, because it was transparent, if you put it on white, it actually looked a little sort of greenish. The brown actually shows through the gold sufficiently to give it this rich reddish colour that was what people were after, so…
Miranda Hinkley: You can actually see that here, on the halo there are certain areas where you can see this really strong reddy brown terracotta colour coming through.
Philip Ball: There are areas here where it looks as though the gold has actually been worn away and you can see the underlayers. So it would be stuck there typically by egg white, by a substance called glare, so egg white mixed with a little bit of water, and that would just be painted over the brown layer and then the gold leaf would be laid down very, very carefully on top of that. It is a very delicate process – anyone who’s ever handled gold leaf very quickly finds out how difficult this stuff is to handle. It sticks to everything, so you had to be quite skilful to be able to apply this stuff…
Miranda Hinkley: And not end up with it all over your tools and your fingers rather than the canvas…
Philip Ball: Exactly. Which is always what’s happened to me when I tried to do it. But once it’s down on the surface, these wooden surfaces even though they might look quite smooth once they’ve been painted with the underlayers, actually there’s lots of little pits and crevices in them and so the gold would stick into all of those and it would look… it wouldn’t look very shiny… it would look a little flat, a little matt, and so to get a shiny surface, the artist would then burnish the gold and this meant rubbing it very gently with a hard object, often a stone, or often actually a tooth, a dog’s tooth was sometimes recommended for this. And this would just smooth down the surface and so that you got this shiny layer.
Miranda Hinkley: So why, Philip, did gold stop being used so much in art works? Because one thing that you notice as you move out of this particular wing is that there’s just a lot less of it.
Philip Ball: Well, in the Middle Ages the main reason gold was used was symbolic. If you were making an altarpiece, as many of these paintings are, and as this picture of Saint Hubert is, then you would want to use the most precious materials to make it an offering to God. But towards the end of the Middle Ages and the beginning of the Renaissance, artists began to be less concerned about those symbolic values and more and more concerned with rendering things as they saw them. And the trouble with gold, if you look at gold leaf, it’s not actually how golden objects tend to look. And this was something that was commented on by Leon Battista Alberti, one of the key art theorists of the early Renaissance in Florence, and he recommended that artists really ought to set aside their gold leaf and start trying to represent golden objects using pigments, so browns and yellows and whites. And he pointed out that if you used gold leaf, the problem was that you were then at the mercy of how the light was falling on the object. You might want the gold to look very bright and shiny, but if the light wasn’t right, it could actually look quite dull, particularly if it was in a church only lit with candlelight. So you could get a much more reliable appearance of gold if you used pigment, so that was really the motivation behind this changeover.
Miranda Hinkley (in the studio): Thanks to Philip Ball.