Collection Care blog

This rather ancient looking Qur’an is deceptively young. In fact, it is thought to date back to the early 18th to late 19th century. The style is typical of African manuscripts originating south of the Sahara, and was presented to Lt. Heygate of the British Army, in Nigeria in 1916.

Front

Front Open

 Above: Manuscript in its wrapper. Below: Manuscript sandwiched between its boards with the wrapper open

It has a number of components; starting from the inside, there is an unbound textblock with thick tanned, haired goatskin boards on top and bottom. This in encased in a goatskin wrapper, which then fits into a goatskin satchel. This multi-faceted construction is similar to other 19th-century Qur’ans from West Africa, south of the Sahara.

Satchel

 Satchel lying on inert grey foam, with acid-free tissue padding to retain shape

First page

 Left: Manuscript open at first page with the letter detailing its origin inserted

As exciting as it is to have this fascinating object in the studio, it is responsible for some real headaches as a result of one particular element of its composition. Before an object comes to the studio to be worked on, a conservator will often carry out an assessment of its condition and write a treatment proposal, estimating the time and materials likely to be used. In this case, when my colleagues carried out the assessment, a large proportion of the textblock was ‘blocking’. This simply means pages were sticking together, which meant that most of the book was unreadable.

Strangely, in the period of time between the book arriving in the studio and the point where I took it out of the safe to work on, around a third of the textblock had released itself. This is not something conservators are trained to expect; most things get worse over time, so to see something improve without our intervention was exciting!

The only conclusion we can come to is that the studio’s environment is slightly different to the one the manuscript came from. The difference in the moisture levels in the air is the most likely culprit. 

Pigment detail

 Detail of yellow pigment, orpiment

On closer inspection the ‘sticky element’ was discovered to be yellow dots painted intermittently within the text areas. These were tested by our Conservation Science team, and found to be orpiment (a poisonous, arsenic-based yellow pigment) mixed in a medium of gelatine. It is the gelatine that is fairly hydrophilic, which would have softened in a humid environment and stuck to anything in direct contact with it.

So the obvious solution to this is to change the humidity levels around the volume further, to release all of the sticky dots. If only it were simple! The brown ink you can see in the image is most likely iron gall ink, which has been used as a writing medium since ancient times. Its main characteristic is that once it’s a few years old it turns from purplish-black to brown. Another, less innocuous ageing property, is its potential to ‘burn’ through the paper it sits on. The extent of the damage can depend on the recipe the scribe followed to make the ink; some are more acidic than others. But it can also depend on the level of humidity the ink has encountered in its lifespan. The introduction of medium to high levels of moisture, even in vapour form, can solubilise ions contained in the ink, which can catalyse the oxidative degradation of the cellulose fibres of the paper. This leads to weakened paper and potentially a severely damaged collection item.

Text

 Detail of one of the illustrations amongst the text

So keeping it dry is the best option for the ink, but pulling apart the pages without moisture could lead to skinning off the top layer of fibres, or even tearing paper.

We’re still deciding what to do about this sticky dilemma, but as ever with conservation decisions, we will have to balance our need to enable access by our readers to collection items with the wellbeing of individual items. Never a dull moment!

Jo Blackburn

When items from the Library’s collection (and from other institutions) are exhibited to the public, it is important to ensure that none of the other materials used as part of the display (fabrics, foams, plastics etc.) will cause problems, for example by becoming acidic or releasing reactive gases as they age. As a result we work closely with the British Library’s Exhibitions Department to test the stability and compatibility of any new materials that are under consideration for use.

The ‘Oddy Test’ is an accelerated corrosion test developed by conservation scientist Andrew Oddy at the British Museum in 1973. It is used to predict potential off-gassing from new materials to determine whether they are safe to use with collection items in an enclosed space. The suitability and compatibility of a material coming into close contact with a collection item is predicted by measuring (semi-quantitatively) the extent to which a new material will release harmful volatiles over a long period. If enclosed in a small space, volatile components such as organic acids, solvents, oxidants and sulphur compounds may reach dangerous levels of concentration capable of damaging objects through corrosion of metals or degradation of organic matter.

Fabrics Testing

 Fabrics for testing

Enclosed spaces could include showcases for exhibition, storage crates, contained shelving or individual item storage boxes. It is important to test all of the materials that the collection item will be exposed to in order to ensure the item is not at risk of damage. For example in the case of a new storage box for loan transport we would test a small sample (approximately 1g) of the board, fabric, adhesives and foam which make up the box.

Method

The original Oddy Test has since been developed into the 'three-in-one' method, but the theory is the same. In the original setup samples of the material in question are placed into three separate test tubes. Approximately 1 ml of de-ionised water is placed in a vial inside each of the test tubes to maintain a high relative humidity. In the first test tube a clean metal token of copper (Cu) is suspended over the sample on polyester thread, in the second a token of silver (Ag), and in the third a token of lead (Pb).

The Oddy Test

 Schematic of the 'three-in-one' Oddy Test. Image source

The test is evaluating the extent to which a new material corrodes these metals, and any alloys containing them. Copper, silver and lead are used because they react to a different set of gaseous pollutants, but results are applicable to all material types. Copper detects chloride, oxide and sulphur compounds, silver detects reduced sulphur compounds and carbonyl sulphides and lead detects organic acids, aldehyde, and acidic gases. Three identical test tubes with metal tokens and de-ionised water are setup as a control.

The containers are sealed up with glass stoppers and secured in place with heat-shrink tubing. To mimic the aging conditions they are placed into a heated oven held at 60 °C. This replicates a ‘natural’ ageing process of approximately 5-6 years. When 28 days have passed the containers are removed from the oven and the tokens are examined. The presence of volatiles is indicated by any corrosion or tarnishing of the tokens. The extent of corrosion gives a rough indication of the level of off-gassing. If the tokens show no signs of corrosion then the material is deemed suitable for use with collection items. 

Oddy tests in the oven

 Sealed jars containing Oddy Tests in an aging oven. Image source

Further Oddy Test developments have seen the 'three-in-one' test where all three metal tokens are placed in the same container over the sample, making sure they are not touching each other or the sample. The interpretation of the results is somewhat subjective given that visual cues such as changes in lustre, colour or texture are used to classify the suitability of the test material for use.

Stability of the materials can be further tested with the use of Image Permanence Institute ‘A/D’ strips. These strips measure the short-term release of volatile organic acids. Oddy testing is just one of several tests that a material must pass before it is accepted for use near a collection item. For example infrared spectroscopy allows us to determine the chemical composition of the sample, enabling us to predict its likely behaviour. Surface pH measurements give an indication of the way in which the acidity of the bulk sample changes over time.

By working with conservators and the Exhibitions Department in this way, we help to ensure that the Library’s collection can not only be displayed in the best possible manner, but that it is also preserved for future generations.

Christina Duffy (@DuffyChristina) and Paul Garside

Further reading

The British Museum published the results of material test results (Oddy and pH) carried out on materials at the BM from 1996-2004

Bamberger et al., Studies in Conservation, Vol. 44, No. 2 (1999), pp. 86-90

Robinett and Thickett, Studies in Conservation, Vol. 48, No. 4 (2003), pp. 263-268

In February this year the British Library hosted a course called ‘Recreating the Medieval Palette’ run by pigment expert Cheryl Porter who is also Director of the Montefiascone Project and a freelance conservator. Those of us attending were a small group of conservators and material specialists from the British Library and other institutions hoping to deepen our knowledge of the materials we work with. The course was an interesting mixture of theory and practice, with the morning lectures covering the basic colour groups and the afternoons providing a more hands-on approach giving us the opportunity to prepare and paint out the pigments and inks on a variety of papers and parchment.

Recreating the Medieval Palette

 The group painting out some examples of earth colours made from rocks and minerals – the oldest pigments used by our ancestors

Alongside the history and manufacturing processes of the pigments we learnt about their chemical composition, visual characteristics, behaviour in response to their environment and modes of deterioration. This is essential background knowledge when undertaking a conservation treatment.

The medieval alchemists didn’t worry too much about health and safety in their search for vivid and enduring colours; hence the highly poisonous production methods for concocting pigments such as lead white, red lead, lead tin yellow, verdigris and cinnabar/vermilion. When preparing the pigments for painting, the powder has to be mixed with a binding medium to give viscosity and adhere it to the page. We experimented with different binding agents – egg white and gum arabic – which changed the working characteristics of the pigments when painted out.

Malachite

 Malachite or ‘mountain green’; a naturally mined carbonate of copper

Lead grinding

 Grinding lead white pigment on glass in a figure-of-eight motion

Making some of the lake colours provided an opportunity to see some real alchemy. A lake is a dyestuff made from organic matter which is precipitated onto a colourless mineral base. Plants such as buckthorn, weld and saffron were used to make a variety of colours, and insects such as kermes and cochineal produced shades of red.

Mixing saffron

Painted-out medieval blues

 Left: Experimenting with mixing saffron (yellow) with verdigris (green). Right: Painted-out medieval blues; the brighter colours are mineral-based azurite and ultramarine and the subtler shades, indigo and woad

We also had an opportunity to learn about inks used in manuscripts. This was extremely interesting from a conservator’s point of view as we discovered that inks can often be identified by the way in which they deteriorate over time. The earliest writing implements were reed pen and quill, and the group’s attempts at writing with these proved that both skill and practice were required!

Reed pen

Quill pen

 Left: Practising writing with reed and quill pens. Right: A quill and block of Chinese carbon ink

Colour sample sheet

   Left: One participant's colour sample sheets

 At the end of this highly informative and entertaining week we went away having learnt a lot from Cheryl’s wealth of knowledge and experience, as well as having enjoyed stories of her adventures collecting and researching pigments. Our array of sample sheets will also provide a valuable visual and chemical reference for identifying pigments in the future.

Vicky West

We recently rehung the R.B. Kitaj Tapestry If not, not in the St Pancras Entrance Hall after it was removed for conservation cleaning. You can read about the process and all the gritty details (hoho!) here.

Working with a 6.75 metres high by 6.75 metres wide tapestry is no mean feat and required the help of many people, so we thought we would honour all those involved by immortalising them in a time-lapse video! (Best viewed with Chrome)

The rehanging required the erection of scaffolding several days before and the hoisting of the tapestry up to the top platform. For safety purposes the rehanging was undertaken under darkness when the library was closed to the public. It was just like Night at the Museum, but in a library...and without anything coming alive...but exciting nonetheless.

Collection Care staff were guided by tapestry experts from Textile Conservation Ltd. and we are really pleased with the result. Come visit the British Library and take a look for yourself!

Christina Duffy (@DuffyChristina)

Our next exhibition; Comics Unmasked, Art and Anarchy in the UK, opening on
May 2nd, will be a surprising one to many. It promises to challenge myths, expectations and stereotypes; and to explore subjects such as politics, violence, gender, sexuality and breaking social conventions.

The relatively good condition of most of the comics from our collection certainly challenged our expectations. For a number of readers, myself included, comics are seen as a relatively modern and populist genre, with striking graphics and minimum text. Conservators often associate anything modern (i.e. 20th century) and mass produced with poor quality paper; similar to the paper used for newspapers that becomes friable and yellows quickly when exposed to light. A few such items, one example shown below, did come to the studio requiring minor edge and tear repairs, but contrary to our expectations the majority of the comics were printed on good quality, often glossy, paper.

Matching tissue paper to support the damaged edge.

Conservation is usually very privileged in getting a preview on the items going into the exhibition, but not this time. Out of over 200 items prepared for display only a handful required conservation work. In the majority of cases the work was limited to flattening of folded pages followed by mounting or supporting a concertina style strip within a book.

Pressing objects between wooden boards

Comic strip opened up and supported within a volume

The first items to be prepared for the exhibition were not that recent either, one example being: ‘The Scourge of Monthly Expositor of Imposture and Folly’ from 1813 showing John Bull preparing for General Congress. This item also needed repair to the edges and mounting.

Concertina style comic strip before conservation

With objects from our collection being in ship-shape condition and one third of all objects in this exhibition coming from other institutions, conservation had a lot more work to do on loans. All items loaned had to be condition checked, some in-situ and others in the studio. Most of those worked on in the studio were paper-based, but we also condition checked unusual objects, such as Judge Dredd’s Helmet and Ally Sloper's Ventriloquist Dummy!

Ally Sloper's Ventriloquist Dummy

  Left: 

Sadly, we didn’t get any visits from Superman, Spiderman or Catwoman in the studio; but we did get to meet a ‘super heroine’ when the new poster advertising the exhibition was unveiled in the St Pancras Entrance Hall in mid-March!

The Comics Unmasked exhibition will be the UK’s largest exhibition tracing the history of the British mainstream and underground comics. It is a must for all lovers of comics, while for others it will be a trip down memory lane re-visiting well known comic characters, and meeting those we heard about but never met!

The exhibition poster showing a female posing after vanquishing a generic super hero

Iwona Jurkiewicz

The R. B. Kitaj Tapestry If not, not was rehung in the St Pancras Entrance Hall last Monday night after being removed for intense conservation cleaning. The tapestry is based on the painting of the same name by R.B. Kitaj, and measures 6.75 metres high and 6.75 metres long; it was the largest in the world when created by the Master Weavers of the Edinburgh Tapestry Company for the British Library. The tapestry had not been cleaned since its installation at St Pancras in 1997 and was displaying visible surface dust which had to be removed.

View of the British Library foyer with the Kitaj Tapestry hanging on the wall

 The Kitaj tapestry

The tapestry was taken down on 28 September 2012 by Collection Care staff guided by experts from Textile Conservation Ltd. who would undertake the mammoth task of cleaning at their studio in Bristol. 

The tapestry was taken down and rolled before being taken away for intense conservation cleaning

Samples of thread of various colour and locations were removed to monitor fading and colour change in the tapestry. A remarkable eight miles of  warp was threaded vertically between steel rollers during its production.

View of the vibrant threads on the back of the tapestry after being removed from the wall.

The tapestry was originally hung using lengths of beige hook and loop fastener. Six lengths divided into three pairs (10 cm apart) were stitched along the top edge. Along the sides were lengths measuring about 55 cm with gaps. These lengths were removed and the turned in sides were released by cutting and removing the stitching. It was here where casings from carpet beetle larvae and degraded moth cases were found. Luckily these were desiccated and no signs of damage were apparent. (Read more about how we deal with pests in a previous post: The Bookie Monster: attack of the creepy crawlies!).

Where to start with cleaning such a huge tapestry? With a hoover of course! The optimum level of suction was determined and the entire front and back surfaces were cleaned using a low powered vacuum suction. The hoover dust consisted of fine dust, brick dust and larger fibrous dirt found mainly on the front. This bag of dust has been retained by Collection Care staff for further scientific analysis. We are very serious when it comes to dust as you may have read in A-a-a-chooo! Collection Care’s Dust Busters.

Once clean it was important to ensure that no insects or eggs remained in the weave. The tapestry was rolled and taken to Harwell Document Restoration Services where it was placed in a freezer unit at -18°C for two weeks. It was fully defrosted over four days and taken back to Textile Conservation Ltd. where a new lining and Velcro hanging system were attached, as well as reinforcement work on any loose stitching. It was then rolled with interleaving layers of tissue and wadding and wrapped in Tyvek and bubble wrap before making its way back home to the British Library.

The tapestry was scheduled to be rehung on the opposite wall to where it was originally placed providing a wider range of viewing angles, and allowing visitors to get up-close to the tapestry on the stair levels. An impressive scaffolding system was erected and new battens were attached to the wall. The tapestry was hoisted up to the top platform after a thorough treble check that it was facing the correct way around!

Scaffolding assembled.

 The tapestry was placed on the upper platform when the scaffolding was fully installed

The Textile Conservation Ltd team took the top platform and began by attaching the top Velcro strips to the horizontal battens.

Conservators preparing for the reinstallation of the tapestry

The tapestry was then carefully lowered down in stages by scaffolders. 

Lowering the tapestry

This provided a controlled unrolling allowing Collection Care staff to hook the sides onto the battens without any air gaps.

Protective tissue paper was removed as the tapestry was unrolled.

 Protective tissue paper was removed as the tapestry was unrolled

When the scaffolding was removed a few days later the final result was terrific!

The R.B. Kitaj tapestry

The tapestry has regained its vibrancy of colour and is a magnificent feature in the British Library Entrance Hall. You can read more about the construction of the tapestry in this Telegraph article from 1997, and more about the artist in the National Galleries of Scotland website.

Christina Duffy

With St Patrick’s Day upon us it seemed fitting to take a closer look at some green pigments used throughout art and history.

Green earth pigment

Green earth pigment (or Terre Verte, Stone Green, Verdetta, Celadonite) is composed of clay coloured by iron oxide, magnesium, aluminium silicate, or potassium. The clay was crushed, washed and powdered. It was used since the time of the Roman Empire until the end of the Renaissance and was highly popular in medieval painting, especially for underpainting of fleshtones. An example is shown below in The Annunciation (1398-1311) by Duccio di Buoninsegna. Here faces were first painted with the green pigment and then overlaid with pink to give a realistic hue. In this case the pink has faded giving the impression of green skin. Green earth pigment was sourced from regions in the south of France and in Italy around Verona.

The Annunciation by Duccio di Buoninsegna: The Archangel Gabriel announces to the Virgin that she will be visited by the Holy Spirit and bear the son of God. Held at the National Gallery

Malachite

Malachite is a copper carbonate hydroxide mineral (copper(II) carbonate), and is green due to the presence of copper. It was used as a mineral pigment in green paints from antiquity until about 1800. It is fairly lightfast and very sensitive to acids meaning its colour can vary.

Brazilian malachite specimen highlighted by spheroidal rosettes of azurite (source) 

Artist Pietro Perugino used finely ground malachite in his 1503 painting Nativity to colour the bright green garments of the worshippers. 

Green pigment malachite is found in Nativity by Pietro Perugino (1448-1523)

Malachite has also been found in the King George III copy of the Gutenberg Bible, held at the British Library using Raman Analysis.

Gutenberg's (42-line) Bible: Opening of Proverbs. Johann Gutenberg, Johann Fust and Peter Schoeffer. Mainz, 1455 British Library C.9.d.4, f.1. Copyright the British Library Board

Cobalt green

Cobalt green is a moderately bright and translucent, but highly permanent, green pigment. The compound is formed by heating a mixture of cobalt (II) oxide and zinc oxide and was discovered in 1780 by Swedish chemist Sven Rinman. It can be mixed with other pigments and is also known as Rinman’s Green or Zinc Green.

Cobalt green (source)

Cobalt green was never very popular due to its high cost and weak tinting power. Researchers at the University of Washington have discovered that cobalt green possesses special magnetic properties and is now being used in the field of spintronics. Spintronic devices are used for computer storage and memory. Cobalt green has found success with spintronic devices as it can be used at room temperature while other materials must be super cooled.

Verdigris

This is a basic copper acetate and is formed when copper is exposed to acetic acid vapours.  The natural patina that forms on copper roofs is often called verdigris, but in non-polluted areas it is in fact malachite (basic copper carbonate).  In polluted areas, though, it is antlerite, a basic copper sulphate.  They are all similar colours so are easily confused, but verdigris in particular causes problems in manuscripts – it goes brown and can burn through the parchment and cause staining on adjacent folios. Verdigris has been used on murals in Pompeii, throughout the Renaissance and on medieval manuscripts including the Lindisfarne Gospels and Book of Kells.

Verdigris (source) 

Verdigris was found to be unstable and unwilling to mix easily with other pigments. In fact the great Leonardo da Vinci warned against its use in his treatise on painting and was leter replaced by the more stable Chrome Green.

Verdigris has been used to decorate the initials on f44v of the Lindisfarne Gospels shown here at 50x magnification (see here for more microscopy images of the Lindisfarne Gospels)

Viridian

Viridian was patented in 1859 and is a hydrated chromium(III) oxide Cr2O3 pigment described as a dark shade of spring green.

Viridian (source)

Viridian was used by Vincent van Gogh in many of his works including Café Terrace at Night, 1888 (Kröller-Müller Museum, Otterlo) and the Night Café (Yale University Art Gallery). Van Gogh to his brother Theo in 1888: "I sought to express with red and green the terrible human passions. The hall is blood red and pale yellow, with a green billiard table in the center, and four lamps of lemon yellow, with rays of orange and green. Everywhere it is a battle and antithesis of the most different reds and greens.” [1]

 Artist Vincent van Gogh (1853-1890) The Night Café, 1888. Oil on canvas currently at Yale University Art Gallery

In many cases a combination of pigments was used to create green colour. Recent analysis of the Sir Gawain and the Green Knight manuscript have shown that indigo (blue) over orpiment (yellow) was used in some areas, while a single mineral green was used in others.

 Sir Gawain and the Green Knight, Cotton Nero Ax folio 129v

Christina Duffy

Reference: [1] Vincent van Gogh, Corréspondénce general, number 533, cited by John Gage, Practice and Meaning from Antiquity to Abstraction

Flavio Marzo, Conservation Studio Manager for the British Library/Qatar Foundation digitisation project reports on the conservation of three manuscripts from the India Office Records.

A new conservation studio has been set up at the British Library to support a digitisation project as part of the British Library Qatar Foundation Partnership programme. The Library’s Arabic material has been scoped for the creation of a new web portal where, in a year’s time, around 500,000 images will be made available online to the general public.

Front left board of MS IOR/R/15/1/105

The majority of material identified for digitisation comes from the India Office records. Many of the files that form this collection are related to the Gulf area, and so are deeply connected to the history of Qatar and its neighboring countries.

The India Office Records are a very large collection of documents relating to the administration of India from 1600 – 1947, the period which spans Company and British rule in India. The archive is held here at the Library and is publicly accessible.

As the formal document of British presence in the Persian Gulf, IOR/R/15 is a fascinating series within the India Office Records, giving a unique insight into a colonial encounter between European imperial power and tribal shaikhdoms on the Arabian Peninsula coast.

One of the most striking features of these Records is the variety and mixture of formats and features related to different manufacturing techniques. These range from bound printed or manuscript volumes to folders containing loose leaves, folded maps, photographs, miscellaneous textile offcuts and samples of products sold in the colonies during the English occupation. In many cases these records were produced by a local workforce in the countries where the IOR officers were stationed.

This mixture of local craftsmanship and foreign taste (and in some cases even foreign materials) has produced very interesting objects which carry a fusion of western appearance and “Islamic” manufacturing techniques.

In this post I want to present some features of three bound manuscripts from the India Office Records: IOR/R/15/1/105, IOR/R/15/103 and IOR/15/1/161.

Front left board of MS IOR/R/15/1/161

Front left board of MS IOR/R/15/1/103

These manuscripts were produced in the middle of the 19th century and contain collections of letters sent from the British Political Residency in the Persian Gulf stationed at Bushire (or Bushehr) on the south western coast of Iran.

Many of the features of these volumes are traditionally considered to be Western. They were all bound in full leather and decorated with similar finishing tools without the use of gold (blind tooled decoration).

Detail of the tool used to decorate the cover of two of the manuscripts

Detail of the tool used to decorate the cover of two of the manuscripts

They are written in English on western handmade paper. The countermark in the image below indicates that the paper was produced in 1843 in Stowford Mill, which continues to make paper to this day.

Page from one of the volumes, photographed in transmitted light to reveal the countermark

Other aspects of these books have been produced using ‘Islamic’ style binding techniques. For example, the textblock sections are secured with ‘unsupported sewing’. The Western binding technique of using a material (vellum or cord) to sew around, attaching the sections to it using the thread, is absent here meaning that it is only the thread itself securing the sections together.

Another example is the execution of the endbands that you see in the images below. These are typical of Islamic bindings as commonly recognized in the field of the history book by the way they are sewn and by the final pattern and appearance.

Islamic style endband

Islamic style endband

It is clear from this mixing of binding influences that these volumes were not produced in a Western bindery! It is likely that the materials were provided by the India Office, along with specific requests regarding the appearance, which tie in with traditional Western tastes. The rest was down to the knowledge and expertise of the local binders, and what an exciting interesting fusion of styles it has resulted in!

The writing close to the gutter of the book can make it difficult for digitisation.

In these specific cases, we re-housed the books in custom made archival boxes and repaired enough of the damaged paper and boards to stabilise it for future handling.

They will soon be fully digitized and available online on the Qatar National Library web site. The process of digitisation gives conservators the opportunity to assess large numbers of items in a short period of time, enabling them to more fully understand the collection. In this case, it allowed me to appreciate the fusion of binding styles that make these items so interesting. Their content will be made available and their peculiar and unique features will be preserved.

The final product!

Flavio Marzo

Purple coloured pages of vellum are sometimes found in sacred texts adorned in gold or silver lettering. They can be seen in folios 2-5 of the recently digitised Cotton Titus C XV on the British Library's Digitised Manuscripts website. Fragments of the Codex Purpureus Petrolpolitanus (a 6th century copy of the Four Gospels in Greek) demonstrate the use of purple as an indicator of wealth, power and kingship. Purple parchment was once only used for Roman or Byzantine Emperors, but later found use in Anglo-Saxon illuminated manuscripts for the Emperors in Carolingian art and Ottonian art. The discovery of shell fragments in archaeological sites in Scotland and Ireland has pointed to the harvesting of sea snails for a gland which produces the purple colour. 

Figure 1: Fragment of the Codex Purpureus Petropolitanus, 6th century, Cotton MS Titus C XV, f. 4v. Read more about this codex on the BL Medieval blog: A Papyrus Puzzle and Some Purple Parchment. 

In 1992 marine shell remains were recovered from caves in Sutherland County in Scotland. Archaeologists used sieves to isolate shells of the whelk known scientifically as Buccinum undatum. These whelks survive in shallow water (down to about 100m) and are found in sand and mud. Their usual capture occurs using baskets or baited pots. The fragmented state of the shells dispersed around the site suggested that they had been purposely collected and broken.

Figure 2:  The sea snail Buccinum undatum.

Another type of whelk mollusc, known as Nucella lapillus (dogwhelk or Purpura lapillus) was found at the Scottish site in Wetweather Cave. Nucella lapillus are found in crevices around rocky shores and estuarine conditions. They are a species of predatory sea snail found around the coasts of Europe and in the north west Atlantic coast of North America where they feed on barnacles and mussels. The deliberately broken shells indicated to researchers that the whelks, which are not edible and were not being used as fishing bait, were being gathered for the production of purple dye.

Figure 3: Nucella lapillus feeding on barnacles. 

Nucella lapillus was also found in Connemara in the West of Ireland in 1919 by J. Wilfred Jackson. Heaps of shells (referred to as Purpura-mounds) had previously been found in 1895, but Jackson noted that the shells had deliberately broken apical whorls (a whorl being a turn of the whelk's spiral shell), but the lower whorl with the mouth had been left intact. The shells were smashed in such a way as to retain the cumella allowing the beast to be removed easily. It was clearly a serious business with one of the Irish Purpura-mounds measuring about 50 by 14 m  - over 200 whelks were found in a single square foot!

The dye is comprised of a mucous secretion from the sea snail's hypobranchial gland and is an organic compound of bromine. The secreted fluid is released by the sea snail as a defence mechanism when agitated. The secretion can be collected by "milking" the sea snails, however this is a very labour intensive process and more often than not the snails are crushed instead. It can take thousands of snails to produce a single gram of pure dye. After salting, boiling and sitting for a few days the gland fluid begins to turn from a pale cream to a purple colour. This process is accelerated by sun exposure. After about 10 days the dye is ready for use.

Figure 4: A purple parchment page of the 6th century Codex Argenteus with gold and silver lettering. 

Christina Duffy  (@DuffyChristina)

Further reading

Pollard, Tony (2005) 'The excavation of four caves in the Geodha Smoo near Durness, Sutherland'. Scottish Archaeology Internet Report 18

Jackson, J.W. (1917) 'Shells as Evidence of the Migrations of Early Culture'

Henderson, George, Vision and Image in Early Christian England, Cambridge University Press, 1999, paperback edition 2010, Chapter 3, pp.122-135, 'The Colour Purple: A Late Antique Phenomenon and its Anglo-Saxon Reflexes'.

As an Imaging Scientist it is very difficult to look at ordinary objects without wondering what they would look like under a microscope. This was just the case when shown a beautiful printing block with a portrait of Steve Fairbairn, founder of the Head of the River Race, etched on the front. Printing blocks like these were used alongside similar-sized blocks containing type in a printing press to commercially produce images and text for publications. But how does it work?

The Fairbairn printing block, belonging to Pauline Churcher of Thames Rowing Club, consists of type metal (lead, tin and some antimony) with a copper electrolytic layer attached with steel screws to a 21 mm thick wooden block

The Fairbairn printing block, belonging to Pauline Churcher of Thames Rowing Club, consists of type metal (lead, tin and some antimony) with a copper electrolytic layer attached with steel screws to a 21 mm thick wooden block

The traditional printing method of letterpress is capable of printing solid colour from printing plates. In order to convey an image with varying shades and tones using a single colour, a reprographic technique called halftone is used. Halftone simulates continuous tone through the use of dots of various sizes, shape and spacing. The image is broken up into many small solid areas for printing. This gives the illusion of a continuous tone – but if we look up-close, we can see that the image is just an intricate pattern of dots.

Halftoning and halftoning close up: A series of dots of various sizes creates an optical illusion of continuous tone when viewed from a distance

This pattern is created using a printing block with tiny holes etched into a metal plate where ink can sit and be transferred onto paper. Below we see what the Fairbairn printing block looks like at 20x, 50x and 200x magnification.

The Fairbairn printing block at 20x magnification. These three images show the increasing magnification of halftone detail on the printing block (top 20x, centre 50x, bottom 200x). Ink is brushed over the plate and fills the hollows.

The Fairbairn printing block at 50x magnification. These three images show the increasing magnification of halftone detail on the printing block (top 20x, centre 50x, bottom 200x). Ink is brushed over the plate and fills the hollows.

The Fairbairn printing block at 200x magnification. These three images show the increasing magnification of halftone detail on the printing block (top 20x, centre 50x, bottom 200x). Ink is brushed over the plate and fills the hollows.

Before the inception of halftone printing, images were printed in books and periodicals using hand engraved metal plates or wood blocks. Wood engraving involves working an image or group of images into a block of wood for use as a printmaking and letterpress technique. Ink is applied to the face of the block and paper is pressed against it.

In ordinary engraving such as etching, a metal plate is used and is printed by the intaglio method where the ink fills the removed areas. When the excess ink is wiped away a sheet of paper is placed on top of the plate, and a blanket covers both to ensure even pressure when pressing. The paper is pushed onto the ink creating an image.

The idea of halftone printing is attributed to William Fox Talbot in the late 1850’s. There were many different methods to produce the halftoning effect, and the earliest trials involved directly etching the images formed on Daguerreotype metal plates. However, the time and skill required to perform such an etching, the inability to print images next to type, and the quick to wear out fragile plates, meant that the process was impractical for commercial publishing. The turning point came in 1881 when Frederic Ives patented a commercial halftone method in the United States.

Frederic Eugene Ives inserting a Kromogram into his Kromskop, circa 1899

 Frederic Eugene Ives 

Ives wanted to find a process to convert photographs into small black or white lines or dots, and to use a printing block which could be used alongside text blocks in an ordinary printing press. The lines and dots could vary in size, but had to be small enough that from a normal viewing distance they blended together giving the illusion of shades. 

The “Ives’ process” was gradually refined and photographs were rephotographed directly onto a metal plate coated with photoresist (a light sensitive material). The popularity of the process spread quickly and by the 1890’s it was used widely replacing earlier hand-engraved wood block and steel plate illustrations. This was the standard process for photographically illustrating books for the next eighty years.

A 3D rendering and colour scale display of the Fairbairn printing block shows that the depth of the stippling is about 86 microns.

3D visualiation of the halftone printing block. The dots are typically 86 microns in depth

Electrolytic copper layer

Type metal (or hot metal) is the metal alloy used in typefounding and hot metal typesetting. It consists of mostly lead with some tin and antimony. The type metal in this block has a copper electrolytic layer and is screwed onto a wooden block. The electrolytic layer is very thin and can be scratched easily revealing the type metal underneath.

Electrolytic layer scratches at 100x magnification

Image of losses of electrolytic layer at 200x magnification

 The copper electrolytic layer is easily scratched. Areas of damage where the copper electrolytic layer has been lost reveal the type metal (lead with some tin and antimony) underneath

The printing block is backed with a paper sheet and ink stains pervade both the backing sheet and the wood block giving a wonderful insight into the history of the item. We often forget that collectibles which today gather dust were heavily used at some point in their lives.

Profile of the printing block under the microscope lens showing printer’s ink residue and paper backing under magnification

Image taken of the profile of the block at 50x magnification

Halftones are considered to be what is known as a photomechanical or process print. Other photomechanical prints include line blocks, photogravures, photolithographs and collotypes. Digital halftoning replaced photographic halftoning in the 1970’s and the theory forms the basis for how the CMYK colour space works using dots of cyan, magenta, yellow and black. You can read more about CMYK in a previous @BL_CollCare post: What the CMYK? Colour spaces and printing.

The printing block in this article depicts Steve Fairbairn (1862-1938) and was kindly loaned by Pauline Churcher of Thames Rowing Club. The Head of the River Race is a 6.8 km processional rowing race held on the Thames each year from Chiswick to Putney with the tide. It was founded in 1926 by Steve Fairbairn who dedicated his life to the sport by both competing and coaching to high levels. The race began with 23 entries and today boats well over 400 crews. The coveted prize is a bronze cast bust of Steve Fairbairn - which is the image observed in the printing block.

Christina Duffy (@DuffyChristina), Imaging Scientist