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The role of computer technology in analysing art

Whilst working at the Chester Beatty Library with the astonishing Ruzbihan Qur’an, I spent some time wondering whether there were ways in which computers could assist with our analysis of the manuscript. Some things I wanted to find out seemed almost within reach, and certainly could be done manually, such as checking to see whether the jadval (frame lines) were all exactly the same dimensions on each page. A minor thing, but it might help us to understand whether the same mistara (ruling device – see here for some very clear examples) was used throughout. Equally, I wanted to compare other divisions of the layout on each page – the size of the onvan heading panels, and the size and position of the decorative side panels. Any anomalies might help us to understand if different quires were worked on by different people, or using different tools, or maybe just at different times. However, I’m limited by my own knowledge and skills when it comes to this kind of analysis – I can manually take measurements of each page but the book is over 800 pages long, so it would certainly be laborious, and then I would have to pick out of the measurements those which matched and those which differed. I’m fairly competent in Excel so could find a way to do this, but I felt sure there must be easier ways…

…And of course there are, and already some exciting methods are being exploited to interesting ends in the fields of art history, bibliography, and codicology. Since I began thinking about this many examples have crossed my path, including a paper given at TIMA last year by PhD student Alex Brey, who used the statistical programming language R to look for variations within certain elements of a Seljuk Qur’an: for example, to find differences between the verse markers, which may help to identify the presence of different hands. His research aims to find out exactly the things which most intrigue me about Islamic manuscript workshops – how many people may have been involved with producing a manuscript; how tasks were divided up within the studio; and how (or, indeed whether) a consistent design aesthetic was achieved when undoubtedly more than one artist was involved. Alex’s blog also delves into other areas where technology interacts with art history. This post is a very interesting discussion on whether computer vision algorithms can effectively look for compositional similarities in paintings (and indeed, what benefits exist from training computers to do this).

Image matching software is another area of interest for art historians and scholars, and already has some very exciting applications.  This Ukiyo-e Search website looks for similar prints across multiple online collections, meaning that comparing impressions, colours (and fading) and so on of the same print is exceptionally fast and easy. You can also upload your own photo of a print, and search to find matches. The Broadside Ballads Online from the Bodleian Libraries has a similar function called ‘Image Search’- you can clip an area from one of the digitised ballads, and search to see where else it appears. As woodblocks for these ballads were used over and over again, by gathering together all the similar images we can also start to see how the woodblocks age as wormholes and cracks appear as white gaps in the printed image. There are a couple of very good images of this in this blog post: Of ballads and worms.  The degradation of woodblocks can be instrumental when it comes to dating and analysing print impressions: here is an excellent poster from the University of Oxford Department of Engineering Science’s Visual Geometry Group which demonstrates this, and the role computer aided image-match technology can play in understanding the order in which prints were made. In fact, if you don’t follow any of the other links in this post I would still recommend you look at this one!


Love and Devotion at the Bodleian

This week I visited the Bodleian Library’s current exhibition Love and Devotion: From Persia and Beyond, which is dedicated to illuminated manuscripts from the Persian tradition combining poetry and images. The exhibition is the perfect size for this kind of material: small enough to allow one to spend time looking closely at each object, but just big enough to leave one feeling satisfied and better informed.

Some beautiful manuscripts are on display, and the exhibition shares some wonderful stories perhaps less well-known in the Western world, such as the love stories of Layla and Majnun, Khusraw and Shirin, and Yusuf and Zulaykha. My previous post on Persian illuminations at the Chester Beatty Library features illustrations of some of these characters. I was also particularly interested to see a frontispiece signed by the master illuminator and calligrapher Ruzbihan, as whilst at the Chester Beatty Library the conservation studio spent a lot of time conserving a Qur’an signed by him. Ruzbihan came from a family of well-renowned artists and calligraphers, and as well as their skills in book arts they were also responsible for the design of various calligraphic inscriptions on buildings across Shiraz. It was said that artistic competitors of the family were “mere eaters of crumbs from their table”.

The team I worked with at the Chester Beatty are keen to continue research into the Ruzbihan Qur’an, so perhaps in the future I will have more of interest to post here. In the meantime, here is a poster I displayed recently at the Institute of Conservation’s triennial conference, which details a little about the ongoing treatment and research into this beautiful manuscript and the workshop that produced it.

The exhibition at the Bodleian finishes this weekend (April 28th), so please rush to visit it! It is also worth pointing out that their online information about the exhibition is extensive and includes high quality images, as well as a very useful interactive map and timeline.

Mughal art

I’ve just returned from the British Library’s exhibition Mughal India: Art, Culture and Empire which has many beautiful miniatures and manuscripts on display (although in some corners of the exhibition the lighting makes is next to impossible to view them). I kept on getting tangled up with a young man and older lady, perhaps his mother, who pored over the pages of calligraphy whilst I stood next to them leaning as close to the illuminations as I possibly could in order to examine them. I overheard some of their conversations and it seemed he was attending Persian calligraphy classes so was particularly enthusiastic about some of the scripts and hands of master calligraphers on display. It made for a nice atmosphere as I was very happy to be among fellow enthusiasts of this kind of art. However, in spite of the fact that there was a section entitled ‘The Art of Painting’ and many references to how Akbar established a formal art studio, there was virtually nothing about the materials or techniques used. Even the captions for the paintings failed to mention details of media and substrate – annoying as some of them appeared to be on textile rather than paper but no mention of this was made. I think some explanation of how pigments were traded and prepared would definitely assist the viewer in understanding the unique colours and appearance of Mughal art. Anyway, it reminded me of something else in the British Library’s collection which gives a tantalising view of how a Mughal studio may have looked and what tools master artists were using. Image

This colophon portrait from the Khamsa of Nizami (BL Or. MS 12208, f.325v) was added at the request of the Emperor Jahangir and dates from 1611-1620. It shows the scribe of the text Abd al-Rahim at work, whilst the painter of this miniature Dawlat sits opposite, drawing his portrait. It’s interesting to see the tools of their trades around them, including the shells used to store paints in, and reed pens. There is also a box full of instruments that at a glance are hard to identify – it would be great to be able to magnify this image further and try and work out what they all are. Miniatures like this can be really helpful for us to see what they were using, and how they might have worked. This one is clearly fairly idealised; it’s hard to imagine that a master calligrapher could produce beautiful work without having some kind of solid support beneath his paper, but nevertheless it does give some indication as to how the artists involved with book production were working.

Suleyman the Magnificent

Last year I was given the project of conserving and remounting a collection of disbound folios from the wonderful Sultan Suleyman the Magnificent manuscript. It was a fantastic project as I ended up working on 18 folios in total, giving me a chance to really get to look at the pigments, style, and techniques used by the artists. Here is some information about the manuscript on the Chester Beatty Library’s website: Suleyman the Magnificent’s Funeral Procession. Below is one of the wonderful illuminations from the series, showing a river crossing on horseback:

Crossing a river

Crossing a river

Briefly, it’s a Turkish manuscript dating from 1579 (AH 987), commemorating the life and deeds of Sultan Suleyman the Magnificent, who had died just 13 years previously. A bound portion of it survives in the Library, but these 18 folios had been removed and mounted separately, probably at the request of Chester Beatty himself in order to display them more readily. Like many of the disbound folios in our collection, they had been sandwiched between panes of glass taped together at the edges and inlaid into thick window mounts, probably done so that they could be handled easily. However, this mounting method can cause problems – the weight of the glass can flatten any 3-dimensional areas of pigment, and place stress upon the paint layer. Any humidity in-between the glass panes can cause a bloom to appear or in the worst cases (thankfully very rare) pigments or varnish can stick to the glass. Additionally, when such items are requested for photography the reflectance of the glass makes it very difficult to get high-quality digital images.

Before removal of mount - showing old glass panes and discoloured window mount

Before removal of mount – showing old glass panes and discoloured window mount

Several of these folios had been requested for photography, and so it seemed like an excellent opportunity to remove the whole series from glass and re-house them in conservation grade mounts and boxes. Any conservation problems that were observed could be treated at the same time. Upon removal from the glass it became clear that there were a various kinds of damage that would need some attention, the biggest conservation issues being cracking and flaking pigments, and some rather large tears in the paper itself. As I removed each folio from glass I undertook examination and consolidation immediately so that the fragile pigments did not remain at risk for longer than necessary. As is often the case, the white lead and other colours containing this pigment were where the most flaking had occurred.

Once consolidation was complete I was able to repair the tears in the paper. I decide upon two strategies for undertaking this: where the tears extended into painted areas I used remoistenable tissue, made in the studio using a fine kozo tissue and a combination of wheat starch and a special methyl cellulose as the adhesive; but if the tears were just in the undecorated margins I used fresh wheat starch paste and tissue.  The reason for this is that the remoistenable tissue can be reactivated using only a very small amount of moisture, meaning that I could avoid putting the water-sensitive pigments at risk. However, the remoistenable tissue does dry to leave a very slight sparkle – unnoticeable on the glossy pigment surfaces, but potentially distracting in the plain paper margins. Therefore in the margins I used wheat starch paste to complete tear repairs as it dries to a more matte finish.

However, rather than going further into depth about the conservation treatments here, I really wanted to comment further on the details I noticed when examining the folios under a microscope. Pigment consolidation affords the conservator the opportunity to examine more closely the working techniques of the artist, and although missing areas of the paint layer are disappointing to observe they can allow us glimpses into the underdrawing that is usually hidden by the dense pigments above. Here are some of the details that I noticed on this manuscript:

  • Red underdrawing was visible in many places, not only where the surface layer had been lost but also where the outlines had never been filled in.

    Red underdrawing visible showing readjustment of feet

    Red underdrawing visible showing readjustment of feet

  • Interestingly, black underdrawing was also visible – it seems curious that an artist would use two different colours to undertake their sketching out, unless perhaps the intention was that the black remains slightly visible through the pigment layer and then acts as a guideline for the final details.

    Underdrawing visible below pigment losses

    Underdrawing visible below pigment losses

  • From the verso thick layers of underpainting were often visible, showing how the images were built up – solid blocks of colour, to which finer details would be added afterwards.

    Underpainting of basic colours visible from verso

    Underpainting of basic colours visible from versoSame area seen from the front, showing details painted on top of basic coloursSame area seen from the front, showing details painted on top of basic colours

  • A variety of blind tool marks appeared when viewing the illuminations with raking light, including blind ruling to mark out margins and other straight lines, blind compass marks (with holes visible in the middle), and even grids into which patterns could then be slotted.
    Viewed in raking light blind ruling is visible, showing how the page was marked out

    Viewed in raking light blind ruling is visible, showing how the page was marked out

    Compass hole visible in centre of wheel

    Compass hole visible in centre of wheel

    Blind ruled grid below pattern, showing how the space was measured out prior to decoration

    Blind ruled grid below pattern, showing how the space was measured out prior to decoration

  • Gold was used in a variety of ways, including to speckle the paper, draw borders, and to signify gleaming metal armour and other details. Interestingly speckling and gold borders often seem to lie below heavily pigmented areas, showing that perhaps the design of the page layout was more fluid than expected, with the artist adding the figures and scenery having to paint over previously applied gold in many places. This shows how lavishly gold was used, if the workshop could afford to effectively render areas of it invisible.
    A thick gold border has been painted over as the layout of the page changed. As pigment has flaked it has become partially visible again

    A thick gold border has been painted over as the layout of the page changed. As pigment has flaked it has become partially visible again

    Gold speckling is visible in areas of pigment loss - where it was never intended to be visible

    Gold speckling is visible in areas of pigment loss – where it was never intended to be visible

  • Gold was also used alloyed with different metals or mixed with pigments. A combination of yellow and gold seems to appear a few times in these miniatures, and the armour demonstrates several shades of gold.
    Different shades of gold visible

    Different shades of gold visible

    Two different shades of gold are visible: a yellow, more matte gold (possibly mixed with pigment), and a brighter, more burnished gold seen on the helmet and sleeve details.

    Two different shades of gold are visible: a yellow, more matte gold (possibly mixed with pigment), and a brighter, more burnished gold seen on the helmet and sleeve details.

  • Silver also appears in some of the illuminations, although unfortunately it has a tendency to tarnish and blacken. In this manuscript the silver has in places been over-painted with fine black lines that delineate fish and waves in delicate detail.

    Detail of silver used to represent water with fine details of fish and waves painted over the top

    Detail of silver used to represent water with fine details of fish and waves painted over the top

  • Other evidence pointing at the tools and techniques used by the artists include the shape of some of the ruled lines – here you can see how a blown-up detail of a spear appears to split into two, suggesting that a nib rather than a brush was used for this detail. A split reed nib, like a fountain pen nib, would spread if too much pressure was applied and cause this double-line effect. Another possibility is that something like a mapping pen was used.

    Detail of line

    Detail of line

  • Another interesting detail shows how some errors were dealt with – by scraping away the surface of the paper. This was a technique long used by artists and calligraphers that worked with parchment, where the substrate would allow a certain amount of scratching out. Hard Islamic paper due to its surface coatings and burnishing also allows a certain amount of this to take place.

    Detail showing how an erroneous border was scraped away

    Detail showing how an erroneous border was scraped away

Evidence of how such illustrations were created becomes easy to see if you subject them to detailed visual analysis. One can begin to work out the order that such things were created in, even without vast knowledge of the historic treatises, by noticing how pigments overlap (for example, gold borders often have details executed in other colours creeping over them, therefore telling us that the borders were done near the start). It would be really interesting to start cross-referencing some of this visual information against the recipes and guidelines that appear in historical treatises – to see if the working practices recorded in literature are faithful to what was actually taking place on the studio floor.

An illustration from the manuscript showing patterned tents

An illustration from the manuscript showing patterned tents

All images © Courtesy the Chester Beatty Library Trustees

Griffen Mill visit

 The Conservation studio at the Chester Beatty Library uses suppliers of materials and equipment from all over the world; however one of our favourite paper suppliers is right here in Ireland. Chris and Mike at Griffen Mill, based in County Mayo, make handmade papers suitable for conservators and bookbinders – we particularly like to use their Islamic-style paper called Akbar for endleaves. In the spring they kindly agreed to let us visit their papermaking workshop – below are some photos of my attempts at making paper.

Dipping the paper mould

Couching the newly formed sheet

Whilst we were there, Chris directed us in a little investigation into recreating a few historical recipes for the kind of surface tints and coatings that are found on Islamic papers, and we also attempted burnishing the surface to get a high shine. Islamic papers would be carefully prepared prior to calligraphy or illumination taking place, using processes such as tinting (white paper was not favoured), applying a coating, and burnishing. Surface coatings and sizes were used to create a smooth glossy, non-absorbent surface; vital in order to allow the reed pen used for calligraphy to move smoothly across the paper. Burnishing brings a beautiful gloss to the paper, but also helps to make it flexible and supple, and gives the paper the ‘drape’ characteristic of Islamic and Arabic books.

Here are some of the coatings that we tried out: 

  • gum tragacanth: soaked in cold water for 45 minutes and then strained. We painted this on in two layers, allowing it to dry in between. Although it didn’t initially produce a particularly glossy appearance, following burnishing it moved well, felt beautiful, and displayed a soft sheen
  • duck egg ahar: using the whites of duck eggs mixed 50/50 with water, to which we added a few lumps of alum. The mixture was then moved around using fingers to agitate it. It is supposed to eventually curdle, although we found if this did happen it certainly wasn’t visibly evident. After agitating it for about 30 minutes we strained it. For a more comprehensive recipe see the link at the bottom of this post. The ahar was painted on in 2 coats, and was really shiny once dry. The surface burnished up really well
  • tea and saffron tints: white paper was not generally desirable for Islamic works of art – instead a soft tint was preferred. We experimented with gently toning the paper using saffron and tea in water. I have been wondering whether using natural pigments like this might be a suitable way to tone repair papers – however a quick check in the studio showed that tea water has rather a high pH and so might not be suitable. Still, it would be interesting to carry out further tests
  • gelatine: mixing watercolour pigments with 4% gelatine in order to tint and shine at the same time
  • wheat starch paste: mixing pigment with thin wheat starch paste in order to create a tone and gloss simultaneously. This might be a good way to tone up paper for repair of manuscripts, and maybe gives depth rather than just a flat colour. Again, worth further experimentation

In order to burnish the prepared paper, it can be rested on any smooth surface. Curved wooden boards or stones were traditionally used, an image of which can be seen on this blog: The curved surface would’ve limited the amount of movement needed from the papermaker as it reflects the natural reach of the arms. The paper could be rubbed with dry soap prior to burnishing in order to increase the slip of the burnishing stone on the surface. Stones such as agate were traditionally used, but anything smooth such as glass or conch shells were also used. We tried using a round glass paperweight, which worked excellently and was comfortable to hold in the hand.

Burnishing paper

Varying pressure by the burnisher can lead to a visible difference in surface texture and gloss – sometimes burnishing on top of a patterned surface (such as carved wood perhaps) was done deliberately in order to create a subtle pattern in the paper, caused by the recesses and raised areas of the surface below (like taking a rubbing by pressure alone).

Apart from all our discussion and experimentation with Islamic-style methods, we were able to quiz Chris and Mike about many aspects of papermaking and hear about their experience as papermakers. I was particularly impressed by the labour of love it was to move their ‘pig flattener’ (big rollers used for calendaring) down the country lane and into the workshop (which took two days using a winch, a few inches at a time).

The ‘pig flattener’

I highly recommend visiting their website which has many interesting sections, including an illustrated history of papermaking. The online shop provides more details of their papers (the range covers papers for conservation, bookbinding, and artists’ papers) which excitingly now includes two different 19th century-style watercolour papers. Sample books are also available.

Further information about preparing Islamic papers can be found on this wonderful website by a contemporary calligrapher: http:// under tools and techniques for ahar recipes.

Persian and Indian pigments

At the start of this year we had a special guest in the studio in the form of Julia Poirier, a conservator from the Derry and Raphoe Diocesan Library Project, who came to work with us at the Chester Beatty Library for a fortnight. Whilst here, she conserved a collection of disbound Indian illuminations and has written up the project here:

As this followed hot on the heels of my conservation treatment of three Persian illuminated folios, there was lots of talk about the pigments typically used in Indian and Persian art: commonly seen pigments include ultramarine (lapis lazuli), malachite, azurite, verdigris (a general term for copper-based greens), red lead, vermillion, cinnabar, safflower, madder, carmine lakes (kermes and cochineal), orpiment, Indian yellow, lead white, carbon black, and precious silver and gold. However, this list is by no means exhaustive and many more pigments were also used.

In the Conservation lab we have several samples of powdered pigments available for experiments, mainly purchased from the magnificent Cornelissen’s who still supply traditional artists’ pigments. We decided it would be worth mixing up some of these pigments in order to paint out some colour charts which we could then conduct various tests upon.  The pigments we had available included mineral-based (lapis lazuli, azurite, malachite); synthesised pigments based on copper, lead and mercury (verdigris, lead white, red lead, vermillion); an organic red from plant root (rose madder); carbon black, and silver. For more about pigments, Boston’s Museum of Fine Arts has an excellent database.


Aside from the silver, mixing up the pigments followed the same procedure: the powder and a small amount of gum arabic (a binder harvested from the acacia tree) were worked together using a glass muller on a tile, until the particle size of the pigment was reduced and a smooth paint texture was formed. A small amount of water could also be added in order to loosen the viscosity.  We also attempted making a purple pigment by combining lapis lazuli and rose madder, as the conservation of Per 163. 82  had raised questions about which combinations of pigments may have been used to make purples.

Turning silver into a paint proved to be a much more laborious task, as silver leaf and gum arabic were mixed using just fingertips in a shallow bowl (traditionally a shell was probably used as the mixing and storage vessel). Even taking it in turns and working on it for a few hours at a time, it still took several days to break the silver leaf down into particles fine enough to be used as a paint.

Silver leaf

Turning silver leaf into a paint

Once mixed, each pigment was painted out onto Indian Islamic-style paper (surface sized and burnished).  We painted out several squares of each pigment so that we could have a control for each colour, and then separate areas on which we could experiment with applying consolidants.

Verdigris, malachite, azurite, lapis lazuli, rose madder + lapis lazuli, rose madder, vermillion, red lead, lead white, carbon black and silver

Mixing and painting out the pigments was revealing in itself, as we were able to learn first-hand more about the handling properties of each. Some, like the malachite, proved difficult to work with as the particles are large and heavy, making the paint difficult to manipulate. The coverage provided by malachite was also fairly poor, showing why layering of the pigments was a necessary step for miniature artists. Others, such as red lead, provided opaque, even coverage immediately and were fluid and easy to handle.  Two tones of purple were achieved by combining rose madder and lapis lazuli (see below), but it would of course be possible to create further variations using these two pigments.

Lapis lazuli, rose madder, and combinations of the two (middle row)

Following preparation of the pigments and painting out the samples, we were then able to experiment with applying consolidants to some of the samples to see how they reacted. This is an ongoing project which I hope to detail at a later date. In the meantime, I have observed that the silver already shows signs of tarnishing, revealing just how quickly the processes of degradation can take place.  Additionally, we have observed that the carbon black has cracked in places, perhaps suggesting that we had included too much binder in the mixture.

Silver showing signs of tarnishing

For me, perhaps the most useful element of this experiment is that I feel much more able to identify some of these pigments in manuscripts, having had the experience of preparing them myself. The particular, unique tones of malachite, for example, seem suddenly much more obvious to my eye, which can be very useful when deciding upon conservation treatments. I also have renewed respect for the craftsmen that prepared these pigments, as the time and effort taken to grind them down was much greater than I had conceived of.

Persian illuminations

 The three loose folios below are from the Khamsa of Amir Khusraw, an illustrated Persian manuscript in the Chester Beatty Collection, dating from 1485 and produced in Herat. The Khamsa is a collection of five classical romances from the Persian tradition. The romances featured in these particular folios are Shirin and Khusraw (left and centre), and Laila and Majnun (right). 

Persian illuminations are meticulously crafted paintings on paper. The Islamic-style paper used is surface-sized and burnished heavily to provide a smooth, glossy surface for the calligraphers and painters to work upon. The painting is then built up in layers of pigment, burnished between applications in order to create opaque, jewel-like lustrous colours. However, the layered structure of the pigment strata can cause problems with flaking and losses, whilst the characteristics of certain pigments used can cause specific problems: lead white has a tendency to flake, copper and lead- based pigments can cause corrosion and discolour, whilst silver tarnishes quickly (visible in the river in the image above right).

The materials and techniques used therefore mean that flaking pigments can be a problem inherent in this kind of art. Conservation of such objects involves examining the folio methodically under magnification in order to identify flaking, cracking,  and areas of loss, and to ascertain whether there is a risk of further losses being incurred. If at-risk areas are found, the problem pigment can be ‘consolidated’ – this means applying tiny amounts of adhesive to strengthen the bond between paper and pigment. Using a very fine brush, tiny amounts of a cellulose-ether based adhesive are introduced next to the crack or lifting flake. The paper substrate should then absorb the adhesive, and using capillary action drag it through the fibres, so that the adhesive locates itself between pigment and paper without the conservator having to touch the pigment layer directly.

© courtesy of the Trustees of The Chester Beatty Library

Khusraw entertains Shirin at his palace in Armenia (Per 163.82)

This particular folio  exhibited several areas of flaking pigments, visible in the red railings, white tiling, and the purple robe of Shirin herself. The purple pigment proved to be particularly problematic: flakes were exceedingly cupped and lifting, and introducing adhesive around the edges did not seem to encourage the pigment to flatten and re-adhere.
© courtesy of the Trustees of The Chester Beatty Library

Purple pigment under magnification

This image shows the extent to which the flakes curl away from the paper, and how blue underpainting is visible where losses have occurred.   An additional problem was that the small amount of moisture from the adhesive appeared to be causing some mobilisation of the purple pigment (a reaction that has not been seen before), suggesting the presence of an unstable organic red in the make-up of the purple.  This has prompted further research and reading on my behalf into the purples used in Persian manuscripts. Unfortunately, another method attempted (using a nebuliser to introduce a very fine mist of consolidant) did not appear to stabilise the area or secure the lifting flakes either, so in this instance it was decided that the folio is too fragile to be displayed, as further handling and movement could result in pigment loss. Further investigation into what the purple pigment might be may allow us to reassess the treatment of the folio at some point in the future. 

Conservation of the other two folios was much more straightforward. Per 163.120 (Leila and Majnun in the desert) is now on display in The Arts of the Book gallery at the Chester Beatty Library.

All images © courtesy of the Trustees of The Chester Beatty Library