Moses Leaving for Egypt (Perugino)

Transcription

Well, good afternoon, everyone. Welcome to the National Gallery and welcome to the first talk in a series around our new exhibition, Making Colour. My name's Ashok Roy. I'm the Gallery's Director of Collections. And this is Dr Caroline Campbell. Caroline and I have worked together over a number of years to put on the Making Colour exhibition and we thought it would be interesting to have a conversation about some of the aspects of mounting this exhibition; some of the things that we thought about and even some of the things that we haven't been able to include. Obviously, although the Sainsbury Wing galleries are fairly large we are limited in scope in the things that we can show. And you might have noticed that although we've tried to cover all the, sort of, principal colours of the spectrum in the exhibition those of you that have seen the exhibition will realise that we haven't, for example, been able to say anything about the colour black or black pigments or indeed the colour white, if you call white a colour, and white pigments. And we will say a little bit about those subjects during the course of this afternoon. But I'm going to begin just to tell you a little bit about the origins of this exhibition. Not everyone knows that the National Gallery has at the back of the building a scientific laboratory on the top floor. And you can see that there, it faces onto Orange Street right at the back of the Gallery. And that has been there since 1975 when the National Gallery Northern Extension was built. In fact, it's an older institution of the Gallery than 1975 and it moved from another part of the building. The function of the Gallery's scientific laboratory really is to study the National Gallery collection and the primary purpose of that work is to understand paintings better for their conservation needs. Now, as a result of analysing paintings we, of course, have over the years begun to gather a lot of information about the materials used by painters traditionally, or the painters of, the creators of the National Gallery pictures. And so, we've been gathering, or trying, as it were, to write the story of the technique of European painting. And one aspect of that story is the history of the use of colouring materials, that is pigments, in paintings in European works of art. The business of actually analysing paintings is quite a scientific and technological affair and we have in the laboratory, these are some of my colleagues in the scientific department, working with scientific instruments which are, have been chosen as means of understanding the material nature of tiny samples of paint taken from pictures in the collection when they're undergoing conservation treatment. And these samples are taken in order to understand the constitution of paint, including the pigments used by painters. So it's a very scientific and technological matter. Now, we have a bit of a tradition actually at the National Gallery of explaining to our various publics how pictures are made. And, in fact, going back some while we had an exhibition called Art in the Making which concentrated on Rembrandt's painting technique. And this is going back to the late 1980s. And you see here two late, great portraits by Rembrandt and a didactic panel from that exhibition which tried to explain how Rembrandt had created these works of art. And the techniques that we used to elucidate painting technique are the same techniques that we've used in Making Colour to tell our visitors what kind of painting materials, particularly pigments, were involved. And we did the same a little while later for impressionist painting in a second Art in the Making show. We also try to make available to the public information on the techniques of painting in this collection through a regular journal which is published in conventional form. It's called the National Gallery Technical Bulletin. It appears every year. And we make that journal available with no charge on the Gallery's website now so you can explore its content going right back to the foundations of the Technical Bulletin in 1977. So it is a very good way of understanding the techniques of painting in pictures in the collection here. Now, I mentioned the techniques that we use to understand the way paintings are made. One of the classic means is to make what are called paint cross-sections. And you see here a paint cross-section from a picture by Monet. It's actually a 20th Century picture. This is Irises from about, between 1914 and 1917. And this is a tiny really miniscule fragment of paint which is mounted for examination under the microscope. And I show it to you because not only is it very revealing as to Monet's materials, it's also, I think, a very attractive image in its own right. And by looking at a sample such as this we can tell the pigments that Monet used to create that passage of paint. And you can see he's one for mixing a lot of pigment together. In the under-layer which is from a yellowish-green area you can see a deep green pigment, it's a pigment called viridian, a mauve pigment called cobalt violet and a number of other materials. And we're able, if we're not able to identify these pigments just from their optical properties, we're able to tell what they are by analysing samples such as that. I'm now going to hand over to Caroline. Quite a shock to see this image suddenly appearing. No, Ashok and I, as Ashok said, we thought it would be good to talk you through some parts of the exhibition and then also to address the question of why we have addressed certain subjects and why we haven't. And as you'll know, those of you who've seen the exhibition, and those of you who haven't, I hope you enjoy it when you do, we start with a room which is really trying to do a very great deal in a very small amount of space. And it's a room that we discussed, I think, very, very much in the two years that we worked together on the exhibition. I should say that the exhibition, it was originally the idea of our Director, Nicholas Penney, who suggested to Ashok that this would be a wonderful subject for a show. And Ashok and I have worked on it together since I joined the Gallery about a year after the discussions for the exhibition started. And we wanted to really demonstrate, I think, that colour doesn't happen in a vacuum in Western European paintings, that there's a long context for the use of colour. Of course, it's one of the most critical things that any maker, in particular a painter, thinks about. But most of that story had to go from the exhibition because it was too complex. So we're trying to represent, or at least draw attention to the fact that Western European doesn't happen in a vacuum and there's a long tradition of the use of colour in antiquity by the display of this very, very compelling portrait from a Roman mummy; from a mummy of the Antonine period found in Egypt in Hawara in the very early 20th Century. An object dating from the mid-first century AD where the sense of engagement with us, or indeed whoever the beholder of this picture might have been it would have been on the front of a mummy is absolutely extraordinary. The colours are quite different, aren't they, we think, to those used in European painting. That's right and there's a much more limited range, I think, at this period. Did you mention that this is a wax�? I didn't mention that. You should. Well, it's very interesting because this mummy portrait, unlike the pictures in the National Gallery collection, is painted in a medium of melted wax so it's beeswax which is the actual binder for the pigment. It's a very durable technique but it's not very flexible. It's a rather difficult thing to pull off successfully. And one thing that I think is characteristic of wax painting is that it's quite difficult as with tempera painting to get a very subtle modelling of light and shade. So although this is a very wonderful image, it doesn't have the sort of quality of light and shade that an oil painting as a portrait would have. No, absolutely not and that's something, of course, which painters have developed hugely in the 750 years or so that are represented in our collection. So really in this first part of the exhibition we wanted to introduce the concept, something which we all know from our days in primary school, but some of us may have forgotten, the idea that colour theory is really centred around, or the conception of colour, how we conceive, perceive and think about colour, and its expression in the physical form of a painting, in the idea of the primaries. And by this juxtaposition which we make in the show between Crivelli's Saints Peter and St Paul of the 1470s and Annibale Carracci's Domine Quo Vadis of the very early 17th Century, you'll see that in both these pictures, painters are using the idea of the primary colours of red and yellow and blue almost instinctively and before there are theories of colour it's something that painters clearly thought about a great deal. Wouldn't you agree, Ashok? I think that's absolutely right. I think there is an instinctive response to the primary colours which is a human phenomenon and it obviously goes back to before the beginnings of representational art. So I think we've, sort of, come in at a point in the 15th Century but, of course, I think these kinds of responses to colour are much older than that. Absolutely, I mean, they're as old as the objects themselves, or indeed the writing themselves, I mean, from antiquity onwards and clearly that's just too big a subject to really address in the space of the show. But we also wanted to allude to the fact that, of course, there are many theories of colour which very much do impact on Western painters from the 17th Century onwards. And, of course, Newton's findings about light were very important also to colour in pictorial form as well. And we're showing several colour wheels in the exhibition, some on the wall and one by Moses Harris, the entomologist, which you see on the slide here, in a book. It's in a particularly beautiful book that belonged to the painter William Etty and was bequeathed by him to the Royal Academy in the 1840s. Can I just say a thing about the Moses Harris? At the centre you see three coloured triangles of representing the three primary colours and where they overlap they're represented as making the colour black, or absence of colour. And this is quite a new thought, that the primary colours, when combined as pigment or as paint, make a very dark colour. If you actually work with red, blue and yellow, mix them together you get a, sort of, rather, a sort of dark sludgy brown, that's true. But in the theoretical sense, the product is black. So, and, that's very acute of Moses Harris to understand. It is extremely acute of Moses Harris. And isn't it true that he was somebody who looked at butterflies' wings and then tried to expand from that? That's right, although what he didn't know about butterflies' wings, the actual colour in the insect wing doesn't arrive from pigment in general but it arrives from the actual cellular structure of the wing itself and the way that the cells interact with light. And there's no actual pigment there in most cases. It's amazing. But yet he used that to produce a theory of colour which actually works in a pictorial sense. And didn't you tell me he is a printer as well? That' s [overtalking]. That's right. That's right. I found that fascinating when I went to look at the object in the Royal Academy Library about a year-and-a-half ago that he's a printer and so he's very, very, very interested - it's very interesting to have these, you know, one of the art and the science combining and, of course, that's something which we think about here at the Gallery but we suspect that some of our audience don't, we don't think about the crossover of these forms as much as perhaps we should. And we hope the exhibition enables people to do that. One, I just wanted to mention very briefly a subject that Ashok has worked on almost more than anybody, and that's the relationship between new 19th Century theories of colour, particularly this theory by Michel Chevreul who was the director of the Gobelin tapestry workshop in Paris and who produced this fascinating and very, very much used by painters theory of colour. That if you put opposing colours, colours on his colour wheel. I'll see if I can get this to work that are opposite each other, such as blue and orange here, the colours stand out more strongly and really a very classic example of that is Renoir's painting here where you can see the orange-yellow of the skiff against the blue of the water that the two women are boating in. And there is such an interesting conjunction between theories and paintings in the late 19th Century that's almost unsurpassed, isn't it? I think that's right. This particular colour theory or colour effect was one that appealed tremendously to the Impressionists but they couldn't really have exploited it, I don't think, without some of the new inventions on the artist's palette in the 19th Century. And I think the Renoir's a very good example of that because that bright orange colour is actually a new 19th Century pigment called chrome orange. And although you can get a colour which approaches it by mixing red and yellow, you don't quite get the same colour intensity as when the pigment has that intrinsic colour. So the availability of chrome orange and here Renoir set it against another 19th Century invention called cobalt blue exploits this complementary contrast effect at particularly good advantage I think. And as Ashok mentioned, the theory and practice are very strongly connected and artists' materials; I mean, Ashok was just saying that without these new materials the Impressionists couldn't have made these great colouristic effects. And we've tried in a very, very microcosmic way to give just some sense to visitors of, of course, the intrinsic relationship between painting and materials in a juxtaposition of two three objects I thought probably one might not think of doing but it actually works very well, of Elisabeth Vigée Lebrun's self-portrait, which we show on the screen here, where she presents herself as if she is painting outside en plein air wearing this straw hat which itself is a reference to a great portrait by Rubens also in our collection. But in the most perfectly, you know, controlled form; all her colours are laid out on her palette in proper order. She looks as if she never got any mess on her dress when she painted. And then you have the absolutely diametrically opposed example of the reality of Turner's Chelsea palette; a palette found in his Chelsea studio when he died and one of his paint boxes, a medicine box which was repurposed for the purpose of storing his pigments. And Turner's fascinating because he's really at the cusp of this development of technology in this box, there is some paint, there are some bladders filled with paint and then there are also some bottles as well. Exactly. Your making the point about Elisabeth Vigée Lebrun made me think just now what new materials she might have had available to her. And, in fact, looking at this self-portrait, it strikes me there's only one new pigment at that period that appears before this picture was painted. And that's a new blue called Prussian blue which was invented at the beginning of the 18th Century. And I assume, but I don't know, that the sky in this picture must be Prussian blue. It has the look of Prussian blue. I was also sorry, go on. Go on, no. Thinking about Turner, many of you will know that there's a film about Turner's life about to appear, I think in the autumn. And so we are very sorry that it hasn't appeared now so many, many people would come to see his palette and his colour box. But I think we're having an event in early September when two of the people who've been involved in fact I know we are two of the people who've been very much involved in the making of the film are going to come and talk about that. And Joyce Townsend from Tate is also going to talk later in the summer about Turner's materials so we will have some link to it. But it was very good that Ashok mentioned Prussian blue because the rest of the exhibition from this introductory room looks at the colours, though as Ashok said, we haven't really, we haven't treated white or black and we are also looking at some, two colours which are not strictly colours but are important to how we think about Western painting colouristically and that's gold and silver. But that would be to jump ahead. But our exploration of blue starts from the extraordinary stone, the mineral, the semi-precious stone, lapis lazuli which as you probably know was mined from one single source in Afghanistan and then used, brought to Europe along various trade routes and used particularly in painting to give a sense of celestial quality. It's often used, not exclusively of course, for the robe of the Virgin Mary. And in these paintings such as the Giovanni da Milano and the Sassoferrato on the screen there seems to be some connection between the intense blue of this that this mineral produces in pigment form and also the meaning of these paintings, of these devotional works. I think one thing that's very interesting about the images you've chosen is that unusually for a mineral pigment or indeed any source of a pigment, the colour of the mineral, the colour of the pigment particles that you see under the microscope and paint on the picture, they're all very, very consistent. It's exactly the same colours you see in the mineral. Where very often when some natural material is used to generate a pigment, the actual colour you get isn't quite as wonderful as in this case. But this is a unique material and it's a unique colour and I think that was celebrated. That was always celebrated. And, absolutely, but it might be interesting to look at azurite which is another blue mineral which is used more, though not exclusively at all, in northern Europe than in the south of Europe. This is Altdorfer's great painting from the collection of Christ leaving his mother. Because azurite is, of course, a slightly in paint it has an almost green-bluish effect, but that's not quite the colour of the mineral is it? No, not at all. No. By the time you grind the mineral and mix it with medium there's one effect, particularly with oil that the mineral is a copper-containing ore and it's chemically quite active and so it tends to react chemically with paint medium and that tends to shift the colour of the paint. And that's one of the things that goes on so it either darkens in some cases or it becomes greener than perhaps the artist intended. So it doesn't have that stability that ultramarine That ultramarine does. No, exactly. When it's used in and ultramarine is stable whether it's used in either a tempera or in oil, isn't it? Absolutely. Completely. Unlike some other pigments. No, it's one of, it's very interesting to see how painters in the past, possibly more than today were so sensitive to the question of their materials and how their materials reacted when mixed with a particular binding medium. It's something which you had to think much more of, I suspect, when it was more difficult for you to actually get your pigments and your materials of paint. And since there are so many things I want, we want to talk about I thought I might just skip through very quickly into green which is the next room. And we've tried to organise each room really round a, sort of, theme. And one of the themes of green is that you have to think of your medium, the question we've just been discussing, but also the relationship between the development of landscape painting and the and green pigments. Because painters had to mix their pigments really in the earlier period, they had to mix their yellow and their blue together to get green and sometimes that leads to rather unstable results. Although it's not an unstable result in the painting we're looking at here, the Pollaiuolo, but that has darkened because of a material that the painter used, a resin he added and that has the effect that here, the green of the landscape here and also of the tree has become a rather more murky brown, completely unintentionally. I suppose there's a point about landscape painting and colour in general that if you are painting landscapes you have a need for a greater range of greens than any other colour for in a different context. If you want to represent a green drapery, well, you might be guided by the pigment that you have available but if you have to represent nature you need to be accurate in that sort of way, so, you need a great range of colour. And so, hence a lot of mixed pigment. And a lot of thought. And then, of course, the discovery of new pigments in the 19th Century was a complete godsend to painters, wasn't it? It was, yes, particularly amongst the greens, I think, as you say. Yes. And these two pictures which we're showing in the show, a great two landscapes of very similar sizes actually, and rather interesting as a pair together, Philippe Rousseau's mountainous, sort of, valley of 1860 and Cezanne's Hillside in Provence of about 30 years later. And these sorts of effects were only really possible with the new range of green pigments which were available to painters. And they were also stable too, or more so than previous ones. Yes, absolutely, yes. But I suppose in a way the Philippe Rousseau has a slightly different intent in terms of the intensity of the colour that he proposes for his landscape which is a much more, sort of, traditionally naturalistic, kind of, depiction. In fact both landscapes contain a 19th Century invention called viridian which is a very strong, deep green colour. But in the Rousseau it's there in mixed paint and so its, sort of, particular colour quality is a bit submerged. Whereas in the Cezanne it, sort of, sings out at you. Yes. Is it? It's in the dark green, exactly where you are. And then there's another pigment called emerald green which is the middle distance, very intense rather light yellowish green. Exactly. So, that's another 19th Century material. But I think, Ashok, you wanted to say something about one mineral source which we don't� which we're not including in the exhibition which was very important for greens and that's malachite. Exactly. The reason we didn't include malachite as an example of a traditional green pigment is it's quite difficult to find very clear examples of its use in our collection. And yet it's quite an important pigment traditionally, rather more for wall painting and fresco than it is for easel painting. It happens we have in the collection a series of detached frescoes by Domenichino and they show landscapes in which there's a great deal of malachite. It's really the only green pigment. They were rather too large to take Put downstairs. Exactly. But the images you see, just to show you what malachite looks like in its, sort of, massive mineral form, this enormous vase is called the Demidoff Vase, it's in the Metropolitan Museum of Art in New York, and it shows a particular, rather deep, intense green colour of mineral malachite which you would think would make it a very good pigment for all kinds of painting. But it happens that when you grind it up it doesn't have a very intense colour and that's particularly the case when it's mixed with a paint medium like oil. It works quite well in egg tempera, as all pigments which don't have pigments show their intrinsic colour rather better in the egg tempera than they do in oil, generally speaking. But the image you see here; this is malachite which is ground to different levels of fineness. So this is very coarse, this is, sort of, medium coarse and this is fine. And what this shows is, the more you grind it up, the less powerful the colour becomes because the pigment particles scatter a lot of white light instead of just green light. And so you need to, in order to make a workable paint, grind the pigment quite finely. So that makes it less suitable for easel painting than you find in wall painting where it works very well. The example I actually have, this little picture which is connected to the world of Perugino, it's an egg tempera picture and, in fact, there is natural mineral malachite which looks like this under the microscope in the landscape. Of course, this is a picture which is under your curatorship so, where there is malachite in pictures, they tend to be in your pictures. They do, they tend to be in the earlier part of the collection. And this is a very, very beautiful little picture and one which I very much hope we can find a more close attribution than associate of Perugino, don't you? It's a bit of a puzzle, isn't it? It's a bit of a puzzle but it's a very, very, very beautifully and very skilfully painted thing. Yes, I shall pass over this to another moderately early picture but not in this collection. This is a Madonna and child, Virgin and child, by Botticelli which was acquired not so very long ago in a way by the National Gallery in Edinburgh. And it's very interesting, it's a picture in oil and it contains malachite. But it contains, very interestingly from our point of view, two quite different kinds of malachite and you can see that in these paint cross-sections. The paint of the robe, which is a very dark green colour, has these very angular mineral-like particles and these are mineral malachite, bound in egg tempera. But the leaves of the rose are painted with the same pigment but if you look closely at the particle form, these are actually spherical rather than angular. And we used to think that this was a sign that an artificial form of malachite had been used. But it's now known that there is a natural source which has this particular kind of particle form. So although it is possible to find artificial, that is manufactured malachite in paintings, this particular variety probably comes from a natural source in Eastern Europe. So we're very interested to see that this pigment is actually rather more popular than we'd envisaged in particular contexts. And this is one where two different sorts of malachite are in use. And another subject which is really interesting in terms of artists' materials is the connection between technological developments in other art forms and pictures. And one of the most complicated but one of the most important is the question of the relationship between glazes for ceramics and also glass, and its relation particularly to yellow and orange pigments used by painters. In the yellow and orange room and this represents some objects and two pictures which are on show in the yellow and orange room we've tried to tell in rather, sort of, telescopic form a story of the technology of development of these artificial yellow pigments which are based on... they're essentially lead-containing pigments but they also contain another essential ingredient to give the yellow colour and in some cases that ingredient is the metal tin. And in other cases it's another less familiar metal called antimony. And we've found over the years that a lot of Renaissance pigments and slightly later examples of opaque yellows contain either lead and tin or lead and antimony. And we've known rather more recently that there's a whole variety of materials which contain lead, tin and antimony so they're very, sort of, mixed constitutionally. This is a story which is only beginning to be properly unravelled and it's quite a recent thought and discovery that there's a strong connection between the constitution of these yellows and the materials used for ceramic glazing, including this kind of painted majolica ware produced in this case by the Della Robbia workshop. This is an object in the Bargello museum in Florence. And I think it's very interesting because it shows the very consistent palette that you see in this kind of majolica. You see strong greens, which are based on copper. You see very strong mid-blues, which are based on cobalt colorants. And we now know that the yellow is very often based on this antimony yellow colour. And it was probably begin developed by ceramicists as a colouring material for ceramics but we now know that it's something that was transferred to painting, perhaps particularly by the 16th Century and widely in use in the 17th Century. No, and it's wonderful because it's a very stable glaze and, I mean, in an object like this which often I'm not sure about this particular one, but often they're made for outside as well as inside contexts and even after 400, 500 years of being exposed to the wind and the rain they still have the great intensity of the yellows and the blues, of the greens. And this is clearly something which was very appealing to painters as well. Although it's not quite as stable in paint as it is in a fire, in a fired ceramic. I'd never thought of the idea that it had to resist the elements. This is a new thought but, of course, that's absolutely right. And it would have been something that would potentially be quite resistant to weathering in various ways. Of course, the problem with any kind of ceramic, particularly something on the large scale, when you fire it you rely on there being no faults in the glaze to let the water in behind and then, you know, to have deterioration from that source. Looking at this reminds me, some of these very large objects were made in pieces, weren't they? They were. And I think they were assembled as, you know, constituent figures and the background, sort of, done separately. Why do you suppose that was? Is it just a matter of having to work on a large scale and not being able to fire in one go? I suppose it must be in terms of complexity and indeed in one street in Florence, on the Via Nazionale, if I remember correctly, there's a huge tabernacle which is still, you know, open to the elements. I mean, they were incredibly complicated things to make but they really have lasted extraordinarily and the ware is called Della Robbia ware; it's very much associated with this family. In fact they had a, sort of, trade secret in it really. Although there's a very close connection with other forms of decorated terracotta as well, with majolica or painted smaller-scale ware too. What's very interesting, one of the members of the press who came to our press view, I talked to him about the colour scheme of this kind of majolica and he pointed out something which I certainly didn't know or hadn't thought of, that there's no bright red in any of these objects actually. And he also pointed out that there's contemporary Islamic ceramics which have bright red in them, including iznik tiles and so forth. Oh yes, of course they do because they're all red and blue, aren't they? And yet that technology didn't find its way to Europe and become incorporated into this kind of painting which I think is an interesting thought because there are other discoveries made in other cultures which certainly did find their way into Europe. Absolutely. I mean so much in iznik ware is so much collected in Europe and also textiles. I mean, the connection between Turkish textiles and Western European textiles is so intense that sometimes it's almost impossible, or very, very difficult to distinguish between the two. Only the greater specialists maybe this is a good moment to move onto the subject of red. I think it is. Where we're thinking. Yes. Can we just move via, very briefly, via one other yellow point because you've raised that matter and that is other cultures providing technologies and in particular ancient cultural several ancient cultures, we see the beginnings of the use of antimony as a yellow colorant and it goes back certainly to Egyptian times and before. And there's this rather wonderful terracotta relief which comes from a palace at Babylon. This is 600 years old. Here the yellow glaze on the brickwork was done with antimony as the colorant. So, here, ultimately is something that's coming from a culture distant from Europe and also very much earlier than the objects that we've been concerned with. Absolutely, and a very different sort of context of usage as well to most of the paintings in our collection. Exactly. So red; let us Well, red is a vast subject and in for, again, for our red room we've limited to looking at two questions. To looking at vermilion which comes from the mineral cinnabar and also, and as you see in Roman ball painting and also is made in a synthetic form from at least the 8th Century, isn't it? 8th or 9th Century. Just the turn of the 8th and 9th Centuries according to the literature, but yes. And it's a technology which is again, I think, developed in the Islamic world probably and then is used in a more Western European context. Yes, it comes from an Islamic scholar and thinker, a man called Jabir, who was a pharmacist and alchemist essentially and also interested in the origin of materials and alchemy. And, I mean, for me one of the most beautiful juxtapositions in the exhibition has been between these two paintings on the screen. I mean, Masaccio's Two Saints from the late 1420s, from the Santa Maria Maggiore altarpiece and Degas' Woman Having Her Hair Combed from the very end of the 19th, in fact probably also some part of it made in the early 20th Century. And the intense red of Jerome's cloak here is vermilion and it's a wonderful contrast of the differences in this picture of how red lake, which is the other subject of the red room really, which is a pigment which comes from dyes that are used for textiles, mixed here with a bit of white. But the intensity of the red here and also in parts of Degas' painting which is all sorts of different reds, I mean there's an incredible material consistency, isn't there? But very, very different use. Yes I think, is it right that there are four different kinds of red ultimately in the Degas? So there's vermilion, as Caroline says, and there's also a pigment called red lead which is an artificial lead-containing pigment. And that's the more orange-coloured passages here and here. So this is vermilion, this is red lead. And then the darker, more subtle, brownish reds are so-called iron oxide reds like an ochre. In modern terminology they are pigments called such things as Venetian red or Indian red. And they're naturally-occurring earth pigments. And they have a rather wonderful colour quality which is both intense and rather muted at the same time. And then the last red is this, kind of, dyestuff-based pigment that Caroline mentioned which is present in shall I just go back, just for one second? in the blouse of the woman combing the young woman's hair. And that's a very different kind of material and we have a case in the show which shows the origin of the dyestuffs which have been used traditionally both to create pigments for painting and as sources of dyestuffs for dyeing precious textiles, particularly silks. And there are, well, we're representing five main types of the sources of these reds. And we have here, two of which are plant, vegetable in origin. This is something called Brazil wood which is a so called dye wood imported to Europe from the Americas and that is the source of a red dye which could be used to dye textiles or to make a pigment for painting. This is one called madder which is� its root contains a red dyestuff which was used for dyeing and to make pigments. This is called� these three are insect sources. This is something called stick lac and it, these are the secretions of something called the lac insect that lives on a particular kind of tree in India and further East. And that produces a red dye. It also produces a material called shellac which was used as a furniture varnish and so forth. But our interest in it is as the source of this dye for dyeing and pigment making. This is something called kermes which is a European cochineal-like insect. This is actually cochineal which is perhaps more familiar to people as a contemporary, modern source of red dye for, still for dyeing textiles and as a food colouring and so on. Yes, absolutely. So, I mean, what's very lovely about these dye, these pigments based on dyestuffs is that when combined with oil you get the most luscious, I mean, they're sorts of glazes which almost make me think of the effect of, sort of, strawberry jam or something. They're very, very rich and they're very, very beautiful. And particularly when viewed through light they have an astonishing intensity. And when put on top of each other in these glazes' form they're magnificent and I do think Tura's Muse, the sleeve of which we show here, is just such a great example of the sort of expertise and the virtuosity of working with these pigments in oil. And I think you've made the point separately that there must be cases where these textiles represented in paintings are painted with pigments which contain the same dyes as would have been used to dye the textile that is represented, if I can make that circular connection between the various things. Absolutely. There's a wonderful, wonderful connection in this instance, not in this painting but in this form sometimes of the materials really being so closely related. I think because we're, we've so much we want to talk about we might not talk about the question of gold and silver but we might talk about what would you think, stability in paintings or what would you? Yes, maybe, because it's not something we deal with at great length. You probably appreciate that one of the great difficulties for creators of easel paintings is to find materials that are durable over long periods of time. And one problem is pigments can lose their colour; it's a phenomenon that we call fading. Or they can become discoloured. And we see both phenomena in actual pictures. And it happens. Those very beautiful lake pigments which make such lovely glazes on paintings, because they are based on dyes and all dyes are vulnerable to light, those pigments that are created from dyes are themselves vulnerable to light. And there are particular contexts where you see their loss of colour in the pictures. This is a pastel portrait and a pastel is essentially a coloured chalk. And pastels are particularly vulnerable to light and this particular example; you can see that the red coat of the sitter, where that passage of pastel colour's been protected by the frame or the mount for the work, the colour's a lot stronger, whereas the area exposed has faded. So there's a strip of more intense colour at the edge. And unfortunately we know if a picture like this is exposed for long periods to, not exactly intense light, to really any light, it will go on fading. So for pastels in the collection and any works on paper, we make sure that the light levels are even lower than they need to be for other kinds of pictures which are somewhat less vulnerable. But the effect of colour change can be quite dramatic and unexpected. This is a famous now, famous example of most unexpected colour change that was detected when Velásquez Rokeby Venus was included in a temporary exhibition here on Velásquez's painting. We had a chance to examine the picture closely in the conservation studio and it was taken out of its frame to look at the edges of the picture and noticed immediately, it was hard to miss, the fact that you can see that the sheet on which Venus lies goes right to the very edge. And although you can't see on this image, we noticed that the colour was quite different at the edge and although we've always known this picture to have a wonderfully, sort of, subtle dark grey sheet, essentially, in fact, in looking at a cross-sectional sample from the very edge, this is what we saw under the microscope. The surface paint is actually made of blue pigment and a translucent red. This is one of the red lake pigments. And this is, of course, vulnerable to light. And it has essentially lost its colour quite dramatically. And we suspect, or suspect very strongly that Velazquez's original concept for this was a sort of royal deep purple sheet for the Venus. Highly appropriate for Venus, of course, to lie on as the queen of love. Highly appropriate indeed, that's right. Absolutely, and so what we've done, we can't in any way reverse the effects of time on the real picture but what you can do is to digitally reconstruct with a computer image what the picture may have looked like and this was done by our colleague in the scientific department. And this is our belief of something of the original appearance of the Rokeby Venus. Very different sort of image. Yes, it's amazing the difference that that very, very subtle change, in many ways, makes to the whole impression of her and the colouristic effect of the picture. And what we really hope that this exhibition does for our visitors is that it enables people to think a bit more carefully about the relations between the materials of painting and the way the colour effects that artists wish to have, and also of the way in which those have changed. And we hope that after seeing the show you will go back up into the rest of the collection and think a bit more about how the materials are reflected there too. So the exhibition is a beginning of what we hope is a wider exploration of artists' quest for colour and for materials in the National Gallery's collection. Thank you very, very much for coming today. Thank you, Ashok, and thank you for listening so patiently. Thank you very much.