#cuirbouilli

AIC Wiki: BPG Book Decoration

https://www.conservation-wiki.com/wiki/BPG_Book_Decoration

Decorative Techniques

Cuir-bouilli

“A method of decorating a book utilizing the capability of a vegetable tanned leather to be molded when wet. After being thoroughly softened in water the leather can be formed or molded into various shapes, which, on drying, retain those shapes with a remarkable degree of permanence. The wet-mold leather can be more permanently set by drying it under moderate heat, the degree of rigidity obtained cuir-ciselé being determined by the drying temperature. A faster method, and one that produces extremely hard and rigid shapes, is to dip the molded leather into boiling water for anywhere from 20 to 120 seconds. This is the process that gave rise to the name "cuir-bouilli." Such a process involves the partial melting of the fixed tannin aggregates in the leather. At a temperature approaching 100C. these aggregates become plastic and can be made to flow and redistribute themselves throughout the fiber network of the leather. On cooling, the fibers become embedded in what can best be called a tough, three-dimensional, polymer network or resin. [...] The leather actually sets so hard that some books bound in this manner required no boards. The decoration itself was executed by cutting the leather lightly while damp, after which the design was hammered in relief. The shaped leather was then immersed in boiling water, and dried, and the depressions were filled with molten wax so as to preserve the designs.The molding of leather was known in Saxon times in England, and was widely practiced during the middle ages in both England and on the Continent. The motifs used were generally mythological animals and interlaced foliage.” (Roberts & Etherington, 69-70) 

Cuir-cisilé [cut-work]

“A method of decorating a bookbinding in which the design is cut into dampened leather instead of being tooled or blocked. The design is first outlined with a pointed tool and then dampened. It is then brought into relief by depressing the background, usually by stamping a succession of dots into the leather very close together by means of a pointed tool. Certain parts of the design are sometimes embossed from the flesh side of the leather, and in such cases the decorating must be done before covering.This technique of embellishment, which may well have been the highest manifestation of the medieval bookbinder's art, was widely practiced only during the 15th century and only in certain areas, principally southeastern Germany and in Spain. No English and Flemish and practically no Italian examples are known.The finest cuir-ciselé bindings have been identified as the work of Mair Jaffé. More recent (and excellent) examples were produced in France by Marius Michel, c 1866.” (Roberts & Etherington, 70) 

http://jacksparrowcostuming.net/images/sccabards1.pdf

“Leather Decoration an Overview: Decorative Techniques Used

The decorative motifs in medieval leatherwork often seem to echo designs in other media, including stone sculpture and illuminated manuscripts. (Cowgill 40 – 41) The concept of horror vacui is prevalent – the idea that designs be adapted to fill the visible space. (Cowgill 42) This is seen from scabbards to shoes, from belts to boxes. Symmetry and balance are also important design elements. In some cases, the imagery on leather items is very similar to that on woodcuts, with rather flat designs and cross-hatching to delineate background from foreground. Other designs incorporate fairly high relief to create more realism. Color is used to enhance these effects. Abstract designs of floral work and interlace are also very common. The workmanship on medieval leather items ranges from fairly simple and crude to incredibly ornate and skillful.

Based upon images in medieval manuscripts and paintings, many leather items like shoes and accessories were brightly colored. Leather dye soaks into the item to provide all over coloring. A variety of dyes for leather were recorded in The Plictho, a 1548 Italian dye manual by Gioanventura Rosetti. Ways to color leather red, blue, green, yellow, and black were included. (Rosetti 65 - 83; 159 - 180) [...]

Examples of dyes used on vegetable tanned leather are even rarer. There is one simple method to dye vegetable tanned leather black that has been used for a very long time, however. It uses a chemical reaction between the tannins in the leather and iron oxide. This reaction is the basis for oak gall ink, recorded in On Divers Arts by Theophilus in the 12th century (Theophilus 42 - 43). Vegetable tanned leather exposed to rusty water (or a combination of iron and vinegar) will quickly turn black. This is now being used as a spot testto check the tannage of unknown pieces of leather found on archaeological sites. (van-Driel Murray, 2000 316) This reaction also occurs when leather is in contact with iron-rich soil. This can significantly change the color of leather items after burial, making it hard to determine the original color and decoration.

Leather items were also brightly painted, although little paint survives in archaeological contexts. There are several extant European examples of cases painted in a variety of colors, including red, white, and yellow in the German Leather Museum. (Figures 1 – 7) Many of these have a black background, which could either be black paint, or the black iron oxide dye. Traces of cinnabar (vermillion) paint have been found on a girdle from Anglo- Saxon York, (Mould et. al. 3393) as well as on two scabbards from medieval London. (Cowgill 40) In his treatise Il Libro dell'Arte (The Craftsman's Handbook), Cennino Cennini mentions that leather should be coated with gesso before being painted. (108) Oil paints and egg tempera paint will work on leather, but the included examples are probably oil based paint.

The application of gold leaf was used on expensive leather items, particularly book bindings, religious cases, and showpieces like parade shields. This was a very specialized process, since it involved stamping the leather two times with each stamp – once to form the impression and then again to apply the gold. (Waterer, 1968 38; Gall, 1967 28) The stamps had convex decorations, which when pressed on the leather made sunken designs to hold the gold and keep it from getting worn off. They were usually heated, which helped the design stay crisp, since books were often covered in alum tawed leather, which doesnt take stamping very well. (Salaman 1) To apply the gold, the leather was covered with a base coat (usually red paint), followed by a coating of glair (egg white, vinegar, and water) – a process very similar to how gold was applied to illuminations. (Salaman 8; Gall, 1967 28) (Figure 7) [...]

Vegetable tanned leather can be molded into fairly complex shapes, depending on the heat of the water used to dampen it. Cuir bouilli (boiled leather) is a technique used to make very hard leather items like armor and drinking vessels. The water should not be boiling; the best temperature is between 140 and 180°F, based upon personal experience and other re-creationist experiments. Once soaked in the hot water, the leather becomes very elastic and stretchy, and can be formed into curves and shapes. Once it cools, it can still be molded, but not to a great extent. After such heating, the leather is more compact and significantly harder. Leather items can also be dried in an oven on low temperature (approximately 150°F or so) until all the water is evaporated. Such items need a last (mold form) inside to keep the leather from flattening while drying. [...] Items hardened in this way can also be decorated with paints, dyes, and stamping, although stamping must be done after the initial soaking and stretching, but before the final drying for the design to remain clear on the leather. (Figure 12)

Stamping (called engraving or punching in some sources) is probably the most common method of decorating vegetable tanned leather. It depresses areas of the leather, creating designs. The leather is dampened, and then a metal or wooden stamp is pressed into the leather, usually by hitting it with a mallet. Brass or clean (not rusted) iron is used for such tools to prevent dark marks on the leather.

Stamping is easily recognized on items with repeating single motifs, especially on book bindings and scabbards. Many of the stamps were quite simple designs like fleur-de-lis, cinquefoils, and latticework, but more complex designs have also been found. (Figures 13) [...] In contrast to single motif stamps that create a specific image, some designs were created by using a stamp to fill in the background, creating a picture in the negative space. Such designs are contrasted with single motif images because multiple copies of the same subject arent identical. (Cowgill 43; Egan and Pritchard 46) (Figure 3, 4, 6, 14) Backgrounds of round pimpling (Figure 14) were very common.

[...] Designs can also be pressed into the leather using flat and pointed tools that are not hit with a mallet. This technique is called modeling (or engraving in some sources), and can be used to create rounded shapes and figures, and free-form floral designs. These specialized tools can be used much like pencils, with harder pressure making deeper designs. [...]

In contrast to stamping and modeling, embossing pushes the leather up from the underside to make the designs. These appear as low relief raised decoration. Embossed areas often include a leather plug that supports the raised up portions of the design from behind. Most embossed leather items are made from wood and covered with leather, such as box lids or shield covers. This makes it difficult to tell if the design was made from the back (embossing) or from the front (modeling) – in fact, some authors do not distinguish between the two forms. (Cowgill 42) (Figures 1, 4, 5) [...]

Many of these techniques were combined into large scale items, usually boxes and cases covered in leather. (Figures 1 – 7) The German Leather Museum has several cases that appear to combine incising, stamping, and modeling-embossed areas, many of which are brightly painted. Several crown and coronet cases, as well as cases to hold relics and other religious items, are still preserved in museums – often with the original contents. These cases contain a variety of design styles. Many have an all over design of scrollwork, while others display mythological and religious scenes, such as interpretations of Saint George and the Dragon. (Figure 5) Heraldic displays often accompany crown cases, presumably the arms of the royalty.

Comparison to Modern Re-creationist Leatherwork

Modern re-creationists recognize the necessity of leather for items like shoes, belts, and pouches. Items covered in leather, such as boxes, chests, and carrying cases, seem rarer, however. These items appear to have been very common in medieval Europe, but usually arent seen at modern re-creationist events. Many garments would also have been made or trimmed in leather, but are not commonly used by re-creationists.

[...] Most items are not decorated correctly, however. Some re-creationists assume there was no decoration or color at all, based upon utilitarian items found at excavation sites. This is because the leather from these sites comes out of the ground a uniform brown/black color, and most items do not show any original coloration at all. [...]

At the opposite extreme, floral scroll work is common to both modern and medieval leatherwork, but is rarely used for decoration by the re-creationist. The Western Floral and Sheridan type of work is very similar to the scrollwork on many of the cases and boxes, with flowing Acanthus leaves and open circles for specialized decoration. But this type of design is not often pursued by the modern re-creationist. Compare Figure 15 to Figure 18 to see the similarities and differences in the floral work. 

In addition to these examples of period designs and how they are used (or not used) by the modern re- creationist, the way space is filled in can be very different between the modern and extant examples. Many modern examples often contain just one design element, with lots of open space. As can be seen on the extant examples, this was not usually the case for medieval leather items. Virtually all of the items from the German Leather Museum appear to have all visible surfaces covered with designs, some of which do not seem to fit with the main design. This includes small vignette scenes on the sides of boxes, as well as corner decorations that complement the central image. All over designs, and those with all over backgrounds, appear to be almost completely absent in modern re-creationist leatherwork. [...]

The use of color has changed significantly as well. The variety of colors on the German museum pieces is amazing. With the greater range of colors in acrylic paint available to the modern re-creationist, the pure heraldic hues would be easy to reproduce. Most modern leather items are only dyed or very simply painted, though. Painting an entire piece is usually not done, and modern leather dye doesn’t create the same effect seen on the painted originals. Modern leatherworkers will use stains and antiquing techniques to highlight the grain structure, letting the leather show through. The re-creationist leatherworker seems to follow this practice, which appears to be a modern aesthetic rather than a medieval one, based upon the highly painted examples.

Summary 

[...] And the tools of a modern leatherworker may be of zinc covered steel instead of brass or wood, but many of the stamp designs available now would not be out of place in a medieval workshop. 

[...] Modern, rather than medieval, ideas and uses of decorative techniques seem to dominate in re-creationist leatherwork. While these obviously appeal to the modern person, they are not the same as what a medieval European would appreciate in leatherwork. Items decorated in such a way would probably seem very strange and out of place, based upon the extant examples - just as some of those examples seem garish and not what was expected to the modern re-creationist. This difference in appeal is at the heart of the aesthetic difference and makes recreating accurate items difficult.

 http://www.personal.utulsa.edu/~marc-carlson/leather/leather.pdf

Leather-working in the Middle Ages: Period Leather-working techniques: Cuir Bouilli/Hardened Leather FAQ

Authored by: Marc Carlson

“A. Simple Soaking

The first, and the easiest, is to soak the leather in cold water (as long as you want to, suggestions range from 15 minutes to 12 hours or longer) then form it and let it dry. This may not seem all that great, but if you've seen a vambrace after it's been sweated into after a summer, you know it can harden up quite a bit. If you tool the leather while it is wet [hammer it], you will make it even harder.

Soaking leather to make it harder is really more appropriate for vegetable tanned leather.

Some people have suggested soaking the leather in lye or urine, but I have no idea if these actually work any differently than using normal water.

B. Hot Water Soaking

The hotter the water you soak it in, the harder it will be when it dries. However, each bit of leather has it's own point at which the water is TOO hot, and will be cooked by it. [...] It becomes very hard and brittle, but that's the penalty for over ambition.

I tend to get it about as hot as I can stand to put my hand into, and maybe a trifle hotter, but as long as it doesn't burn me, I assume it shouldn't burn the leather. [...] The hotter the water, the more structural changes you get which results in harder leather.

C. Boiling Water Soaking

If you decide that you want to place your leather into boiling water, and be warned that many people consider this a patently silly thing to do, you will want to be prepared to have your leather shrink and harden very quickly. I would advise actually placing the whole form you are working with and keeping it in the boiling water for not more than about 2 minutes. What this does is to cause chemicals in the leather to liquify and polymerize (see later discussion below) until it shrivels into plastic hardness.

D. A Variation on Boiling Water Soaking

If you take cold formed leather and while it is still on the form and pour REALLY hot water over it, letting it drain off [...], it will scald the surface of the leather and harden the outer layer without altering the inner layers at all. By the time the water's soaked the rest of the leather, it has been cooled [...] sufficiently that the temperature's dropped back down to the 120-140F range.

You can also presoak the leather in water, then pour the boiling water on top. This either heats up the water inside the leather, so you don't have to wait for it to soak in, or the cooler water slows the soaking process, letting the outside of the leather harden more fully.

E. Baking

According to J.W. Waterer, Cuir Bouilli is made by soaking vegetable tanned leather in water until it is thoroughly water logged, then molding it to form and drying it in a constant temperature of 50C (or 122F).

Baking the wet leather can make it even harder, say in an oven, but you run the risk of steam scalding it and making it shrink. [...]

Chaucer, in the fourteenth century makes frequent reference to the peculiar form of moulded leather known as cuir bouilli. [...] 

NOTE: When heating the leather, do NOT touch the leather to any hot metal (Since using heated tooling materials is how book leather is embossed). [...]

F. Hammering

http://www.personal.utulsa.edu/~marc-carlson/leather/leather.pdf

Leather-working in the Middle Ages: Period Leather-working techniques: Cuir Bouilli/Hardened Leather FAQ

Authored by: Marc Carlson

“Cuir-bouilli (From the Oxford English Dictionary, 2d Ed.) Forms: 4/5 quir-, quyr- boilly, -boily, -boyly, -boile, -boyl(l)e, quere- boly, qwyrbolle, coerbuille, -boyle, 6 Sc. cur-, corbule. [F., lit."boiled leather."]

Leather boiled or soaked in hot water, and, when soft, moulded or pressed into any required form; on becoming dry and hard it retains the form given to it, and offers considerable resistance to cuts, blows, etc.

The word was in common English use from 14th to 16th c., after which it is not found till modern times, when it appears as borrowed from modern French. 

1375 Barbour Bruce xii. 22 On his basnet hye he bar Ane hat off qwyrbolle. 1386 Chaucer Sir Thopas 164 Hise Iambeux were of quyrboilly [v.r. quereboly]. 1400 Mandeville (Roxb.) xxvi. 123 ai hafe platez made of coerbuille. 1413 Lydg. Pilgr. Sowle iv. xxx. (1483) 80 A feyned hede formed of playstred clothe other of coerboyle. 1513 Douglas ?neis v. vii. 77 Thair harnes thaim semyt for to be Of curbule corvyne sevin gret oxin hydis. 1880 C. G. Leland Minor Arts i. 1 Solid or pressed work, known as cuir bouilli, in which leather after having been boiled and macerated, or rendered perfectly soft, is moulded, stamped, or otherwise worked into form.

Basically Cuir Bouilli is a means of making hardened and stiffened leather. Although there is some disagreement among some leatherworkers as to how this is accomplished, there is a significant amount of evidence to think that it was done by molding wet vegetable tanned leather. This leather can be formed into any number of forms, which, on drying, will retain that shape. The wet leather can be set more firmly by drying it under moderate heat, the degree of rigidity obtained being determined by the drying temperature. A faster method, which produces extremely hard and rigid shapes, is to dip the molded leather into boiling water for anywhere from 20 to 120 seconds. This technique causes the partial melting of the fixed tannin aggregates in the leather, making them plastic, causing them to flow and redistribute themselves throughout the fiber network of the leather. On cooling, the fibers become embedded in what can best be called a tough, three-dimensional, polymer network or resin. [...] 

There is a great deal of confusion about the term "cuir bouilli" in the literature about leather. Some sources seem to think that it was shaped/hardened with wax, others by wetting, shaping, and drying.”

[...] 

By DR OBUV (From the Crispin Coliquy, 21 January - 27 January 1999)

"The cuir bouilli is the leather of ox or cow 'bouilli' in wax mixed with various gums, resins, and pastes, which are kept secret by the sheath and scabbardmakers. Article 13 of the statutes of the sheath and scabbardmakers of Paris, which are dated 12 September 1560, allows that it is forbidden for the trade to make leather bottles with any other leather than cow or ox, because other leathers are not suitable, and that the above-mentioned bottles must be 'boulues' with only new/fresh wax and nothing else, and stitched with double-seams from both sides [i.e. double-looped hand stitch, not a running stitch-ED], strong and durable." -- Roland de la Platiere, 1788 in 'Encyclopedie Methodique' [Paris,1790]

Key here are the various ways in which "bouilli" and "boulues" are used. Literally "boiling" the leather, as in dunking it into a vat of hot waxes is the immediate and easy assumption, but upon removing the object and its "last", the waxes would rapidly cool and leave an object encased in a mess solidified waxes.

"The Shoemaker uses several kinds of wax. [...] Bootmaker's jacking/wax is made from two pounds of collophony [NB -- highly refined/brittle pine rosin from Colophon, Lydia. The German edition has 'pitch' or 'black pitch' here] and one pound of yellow wax [NB -- raw beeswax] with lampblack [NB -- powdered carbon from oil fires] to suit, all melted together. This jacking/wax is used by Bootmakers to penetrate the leather of jack boots and to make them stiff as wood... The Shoemaker uses this wax for certain heavy shoes that the lower sort and peasants wear, but while making it he reduces the amount of colophony."

"Having one pair of boots... over their boot trees and previously wet, but now dry, take a coarse wood rasp, which is rubbed over the whole boot-leg to remove the fluff which stands up on the flesh; after this you proceed with the jacking/waxing... The place for jacking/waxing must be a room with a chimney, paved or tiled [NB-- "...where there is no fear of fire" in one edition]; near the top of the chimney, outside, is attached an iron chain which dangles to within six inches of the floor or there-abouts. You ready yourself for jacking/waxing by putting a small portable stove or lit brazier on a table to your left, on which you place a kettle containing the following recipe: One pound of yellow wax, two pounds of colophony, which is pine rosin, and lampblack to suit. You also furnish yourself with a swab, this is the name of a large dauber formed from a bundle of linen rags bound together, and have on your right, on the ground, some loose straw... Begin your task by lighting a little straw, which you wave under the bootleg to singe it, in other words to burn the rest of the fluff from the leaher that the rasp did not remove; afterward dip the swab in the BOILING [NB -- emphasis added] jacking/wax with which you coat the entire bootleg. Then continually rotate the boot-tree with your hands over a steady straw fire so that the heat makes the jacking/wax penetrate. You put on six sucessive coats in the space of an hour, being very careful to occasionally moisten the bootleg so it will not scorch, and so it takes two hours time to jack/wax one pair of boots. The bootleg now jacked/waxed, leave it to cool... When the bootleg has been jacked/waxed, and once more is thouroughly cold, it is full of lumps caused by the boiling jacking/wax with which it was coated and saturated; to remove them take an old knife, and using the blade as a scraper, scrape off all these lumps, then rub with a piece of cold wax that you spread very evenly with a stiff brush or burnishing stick, etc., and you finish-off by polishing and shining with the palm of your hand". -- M. de Garsault, 'l'Art du Cordonnier' [Paris, 1767]

"Lacquered [NB -- literal translation from German] Boots -- A type of stiff boot with or without tops, which are made with the flesh out in the same manner as the jack-boots, and which are given a glossy finish with the following lacquer:

Powdered gum mastic... 1/2 oz. Powdered ivory-black.... 1 oz. White poppy oil... 1 oz. Spikenard oil... 1/2 oz. Asphalt... 1/2 oz. White wax [*]... 1/2 oz.

Add the ingredients seperately, mix in the oils."--D. G. Schreber, 'Der Schuster' [Leipzig, 1769].

While not necessarily a jacking/wax, this formula is interesting. Schreber discusses the superiority of all English boots, and the polishes for them, but says they can't quite get it right. [*, this usually denotes highly refined beeswax that has been rendered and filtered to the point of being nearly pure white--harder than raw yellow beeswax].

"For Jacking The Flaps of Cartridge Boxes Let the flesh side of the leather be shaved smooth, & put outside. When 'tis well dried & warmed, rub it with the following composition, of: 6 pounds of rosin; 1 pound of beeswax; 1/2 pint of spirits of turpentine} all dissolved together and put on hot. Frequently hold the flap to the fire till enough of the stuff enter the pores of the leather, rubbing well. When cool, size it... with a size made of rawhide, rubbing it well. If spirits of turpentine cannot be had, beeswax will answer; but it does not penetrate the leather so quick... To save the jacking stuff, the flaps should be cut out before they are jacked; but it is said that the jacking should not come where the leather afterwards to be sewed as it will be too hard; ... You will try the jacking, both before and after the sewing, and determine which is the best way." -- Timothy Pickering on Jacking cartridge box flaps, Vol. 56, p. 5 [No date, c. 1775]

"We would go to a turner or wheelwright, and get head blocks turned, of various sizes, according to the heads that had to wear them, in shape resembling a sugar loaf; we would then get some strong upper, or light sole leather, cut it out in shape, close it on the block, then grease it well with tallow, and set it before a warm fire, still on the block, and keep turning it round before the fire, still rubbing on the tallow, until it became almost as hard as a sheet of iron... We made the scabbards of our swords of leather, by closing on a pattern of wood, and treating it similar to the cap." -- Recollections of a Revolutionary War Soldier [reprint 1854 edition]

Now then, as we have before us an accumulation of descriptions of the process of hardening leather with heat, pitch, rosin, etc., let me launch a question... since "bouilli", in Abel Boyer's 'Royal Dictionary Abridged' [London, 1700] gives, in addition to "boiled", "warm, boiled, seething, or bubbling up", "to gush out", and even "baked" in connection with "boul"--derived words, what are we led to believe? Under "cuir" he gives "visage de cuir bouilli'; a wainscot face. P. Faire de cuir d'autrui large courroye, To be free of another man's purse." Now wainscot seems to be a stretch, but the connection with wood [as in Garsault's "hard as wood"] is tempting..

...Firstly, just because Chaucer mentions leg-guards of "quirboily", how/why do we assume it was heat and water only, rather than heat and "bouilli" painted-on? Why not dope-hardened leather? Waterer's assumptions aside, why couldn't Chaucer's "quirboily" be doped-hardened leather in the 14th c. as well? Post 1560 in England and France, the suggestion is saturated with rosin, etc., just that the Brits start calling it "jack"ed by the 17th, and drop the Franco-phonic "quirboily" from the vocabulary all together.

Any confusion here regarding "waxed leather", which I agree is NOT "cuir bouilli", is purely accidental I assure you. The problem is in the French use of "cire" for bloody everything vaguely resembling a waxy substance. A bit of care, however; in my translation from Garsault [above] I carefully wrote jacking/wax, where in the French text it's just "cire" [wax], though the French author seems to use "cire" for everything from currier's dubbing, shoemaker's "coad", and "machine" [white coad], up to and including what Pickering just calls "jacking stuff". Garsault also discusses "heavy waxed shoes", [gros souliers cire's]. In this case he says that the un-dyed and un-curried shoe uppers are smeared with a wax [cire] composed of "mutton tallow, a little wax [cire again -- beeswax presumably] and a little more lampblack". This mixture is applied with a dauber dipped in "le cirage chaud" [the warm wax-mix]. Nothing in the text suggests that this form of "wax" stiffens or hardens anything. Quite the contray, it loads it with warm tallow. As a matter of fact, the English term "waxed leather", as in waxed calf, etc. merely refers to a heavily grease-stuffed, blacked on the flesh, uppers leather. In fact, elsewhere Garsault says that blacking on the flesh is more "English", and the French usually blackened their uppers on the grain with dye or stain rather than sooty grease. In French, "waxed leather" is clearly NOT "cuir bouilli".

(https://www.researchgate.net/publication/285833635)

A 15th-century Flemish enclosed garden in cuir bouilli. Production, degradation and conservation issues of a small painting on leather 

Authored by: Lieve Watteeuw and Marina Van Bos

“ABSTRACT An early 15th-century figurative cuir bouilli coffret lid, with remains of original polychromy, belonging to the town museum in Nivelles (Belgium), was studied and conserved in 2013. Cuir bouilli is the medieval Norman-French term for ‘boiled leather’. The technique was widespread in Flanders and Paris in the High Middle Ages. The scene depicted is an ‘enclosed garden’ with the Virgin and Child. The cuir bouilli artefact has been severely damaged by environmental conditions and previous restorations. There are large lacunas in the deformed and hardened leather support, as well as in the pictorial layers. This paper explores the historical context of the artefact, the production of the material, its use and conservation history. Results of reflectance topographic imaging (RTI) are followed by physicochemical analyses and the treatment protocol to stabilise and validate the importance of this lost technique of medieval leatherworking.”

“The technique of cuir bouilli or boiled leather was popular in Italy, Germany, Paris and Flanders in the High Middle Ages, not only for cup, bottle and relic cases, armour (including parade shields), bookbindings and bookboxes, but also for covering and decorating small, highly sophisticated coffers with chivalric love scenes and other subjects. Paris and Flanders were known for the production and export of these luxury goods through trade routes that reached across Europe (Didier 1978, Cherry 1982). Cuir bouilli objects were produced by specialist leather workers, associated with the guild of the cordoeaniers (Middle Dutch term derived from the French word cordouanier), and needed skilful craftsmanship.”

“Cuir bouilli is a process used to change flexible, vegetable-tanned leather into rigid, moulded and often intricately shaped objects (Davies 2006). For shaping of the vegetable-tanned leather, heat and moisture were used, as indicated by the term ‘boiled leather’. No written medieval sources describing the production of decorated cuir bouilli objects survive, so knowledge of the process relies on the important studies of the Scottish leather historian John William Waterer (Waterer 1981 and 1986). More recently, Davies and Payton (2001) described at least three different ways to make cuir bouilli. Experimental reconstructions of cuir bouilli objects, using different recipes, by a group of leather conservators and craftsmen (Neno et al. 1995, Carlson 2003), found that the leather used would be half or fully tanned and that, in response to different requirements, a large range of methods, materials and techniques could be used in varying combinations.

The hypothetical production stages for relief images like the Nivelles cuir bouilli panel could be as follows: the vegetable-tanned leather, made supple with moisture and heat, was stuffed, shaped and nailed to the rigid wooden coffer support. The stuffing material was probably modelled beeswax or stearin wax. To shape the leather, to create its topography, ‘cushions’ were possibly made by lacing a thread through an awl hole and attaching the flexible leather and stuffing to the rigid wooden support on the bottom. Then the decoration was done: lines were incised through the upper layer of the leather (epidermis) with different thicknesses of knives or needles. Contours were created with deep v-shaped cuts (e.g. the St George figure), decoration with thin incisions (e.g. the leaves of the trees) and final details with a needle point (e.g. the eyes of the figures). On the Nivelles panel, an iron-gall ink was very probably applied to darken the surface (see the analytical results below). For the incision and pouncing stage, the leather was probably kept heated and moistened for suppleness. Once dry, the leather would be hard and rigid. Next, gold and silver foils were applied (e.g. on the halo and the crown of the virgin, on the armour of St George and on the sky background). This was followed by pouncing the leather in the sky with heated metal hand tools, or punches (e.g. the little round shapes in the upper area). Finally, polychrome layers were painted on the leather with a brush and finished with small red and white dots (e.g. the little red dots for the cherries or apples (?) in the trees). No varnish was added by the cordouaniers, but probably a wax layer.” 

“Shape and tool identification with reflectance transformation imaging (RTI)

For better plotting and understanding of the moulding of, and incisions in, the cuir bouilli, the panel was digitized with omnimulti-directional lighting. The technique of the RICH Project portable mini-dome is based on reflectance transformation imaging (RTI), a technique of imaging and interactively displaying objects under 260 varying lighting conditions to reveal surface phenomena (Watteeuw et al. 2013). The shaded and the sketch filters were able to reveal the image and its topography very exactly. The xyz height profile and measuring tool monitored 40 mm depth variance in the panel. The highest point of the topography is the arm of the Virgin, the lowest points are the outer edges. The main v-shaped incisions are 1 mm wide and 0.85 mm deep (e.g. the contour lines of the figure of St George), smaller lines are 0.7 mm wide (e.g. the horizontal lines in the fence) and, finally, the incisions creating St George’s fine hair are 0.5 mm wide and less deep at 0.4 mm. The circular hand tool, or punch, used for the background has an inner diameter of 1.8 mm. The little circles were hand pressed with great regularity, as 21 of them show a variation in depth of between only 0.87 and 0.89 mm. The observations with the RTI technique gave remarkably precise information on the craftsmen’s tools: it was possible to define with certainty three different knives used to incise the image, and one small hand punch used to complete it.”

“For 130 years, the object was stored in an overly dry environment. This caused the leather to shrink and break in several places, specifically in the most fragile areas where the incisions in the leather are deepest. The cross section of a sample (SEM backscattered image) documents the extreme fragility of the leather. The surface wax layer on top of the leather became tacky and brownish.”

“XRF measurement of the silver foil on the armour of the knight. As the x-ray beam penetrates the silver foil, not only is the foil measured but also the underlying layers (Mn, Fe, Cu and Zn are indicative of the iron-gall ink used to darken the leather).”

“Non-invasive x-ray fluorescence analysis was used to reveal the craftsman’s palette. In addition, some small samples were taken for complementary μ-Raman analysis and to illustrate the paint-layer buildup. 

All red parts in the painted scene are vermillion based. The red paint layer is applied directly onto the leather support as evidenced by a paint cross section. The flesh tones contain vermillion in combination with lead white. Lead white is used for the white dots on the angel’s robe and for Mary’s veil. Lead white in combination with orpiment is used for the pale yellow dress of the Virgin. Analysis of the yellow colour of the fence also shows the presence of orpiment. Moreover, orpiment was present in all analysed vegetation areas (like the leaves of the trees or the grass). Although now hardly discernible, the original colour must have been green, meaning that a blue pigment must be present as well as the yellow orpiment. Indigo was recommended by Cennino Cennini: ‘A mixture of some of this color (orpiment) with Bagdad indigo gives a green color for grasses and foliage’. The presence of indigo was confirmed by subsequent μ-Raman analysis of a sample taken from the leaves of the tree in the upper left corner. The bright paint layers were enhanced by gold and silver leaf. Silver leaf was used for the armour of St George. 

The silver leaf, which has now turned almost completely black, originally added to the splendour of the object. A cross section of a sample from the background at the top revealed two layers of metal: the underlying one is gold leaf, the upper one is silver leaf. It is hard to deduce why these two layers were superimposed onto the leather. In some areas of the cuir bouilli panel, no paint is applied, meaning that the colour of the leather forms part of the completed image. As evidenced by XRF analysis, the leather was darkened using iron-gall ink (elements Fe, Cu and Zn). These analyses revealed that the pigments used for painting on the leather are closely linked to the palette used for panel painting in the Low Countries at the beginning of the 15th century. In this context, the Nivelles enclosed garden is a rare addition to the corpus of works in the so-called pre-Eyckian painting tradition.”

“After high-resolution documentation and material analyses, tests were executed to evaluate the flexibility of the extremely hard leather by local relaxation with the ultrasonic mister and Gore-Tex patches. These tests produced no results, as the hardened leather has no hygroscopic characteristics left.”

(https://makersgallery.com/rexlingwood/waterer.pdf)

JOHN WATERER AND THE 'CUIR BOUILLI' CONFUSION

Authored by: Rex Lingwood

Goes into differences of ornate cuir bouilli and functional cuir bouilli. Also discusses temperature effects on shrinkage.

“Leather was in many ways the plastic of former ages, ubiquitous, and extremely diverse in its use. Perhaps for this reason it is less prominent in our historical consciousness than more ‘precious’ materials.”

“The term 'cuir bouilli' has been used to describe leather objects of very different visual styles, sophistication, surface treatment, function and method of construction. John Waterer, co-founder of the Museum of Leathercraft, more than anyone else, attempted to understand what the term meant and what objects are properly described by this term. [...] Much confusion surrounds ‘cuir bouilli’ because of the lack written documentation, and the fragmentary and unreliable nature of the information that survives. His assertion that the literal translation of the term 'cuir bouilli' as boiled leather is “meaningless” will not stand scrutiny. The term needs to be understood as a label, a title, not a description of a process and as such it needs qualification and elaboration [...] Secondly, he identifies 'cuir bouilli' with forming processes and not with leather that has been hardened, which is, I believe, a more appropriate indicator. Boiling leads to shrinkage, which causes hardening. Waterer excludes ornamented work (either stamped incised or repoussé), usually Italian, which had not been formed to any appreciable degree but is hardened. The same distinctive type of leather, similarly decorated, is also used to make dramatically formed hardened objects that he does identify as ‘cuir bouilli’. These decorated objects are hardened by stuffing the leather, not by taking it to shrinkage temperature. Any definition of ‘cuir bouilli’ at this stage is going to be somewhat contingent but it seems to me using hardened leather as the common factor corresponds to the result of ‘boiling’ which involves heat, be it hot water resulting in shrinkage or hot fat or hot resin which harden by stuffing the leather. By equating ‘cuir bouilli’ with formed objects Waterer includes work that while firm and stable in form has not been hardened to the degree we see in objects that been taken to shrinkage temperature or stuffed.”

“Further confusion about 'cuir bouilli’ results from the fact that it has been used to refer to two very different types of work. 1) The bottles, blackjacks and bombards (Figure 1) of which the surviving examples are almost entirely of English origin and 2) the highly decorated sophisticated forms of the largely Italian scroll cases, missal cases (Figure 2), boxes, powder flasks and parade shields. The former are formed then hardened using a hot water based process where at least some of the object, usually the outer surface, is heated to shrinkage temperature3. When the object cools it gets extremely hard and when it dries it is nearly impervious to water, and its shape will not be effected appreciably by rewetting it. This process is irreversible. There are a number of ways this surface hardening could have been achieved including immersing it in boiling water and baking it in an oven. These objects are usually japanned.”

“Japanning is a finish (usually black) made of linseed oil and lamp black which is brushed on to the leather in layers and heated and gives the leather a smooth glossy surface.”

“A water hardening process could not have produced the second body of work because the shrinkage it causes would severely distort or completely eliminate the extremely detailed decoration. This work also has a characteristic black colour, which in this highly decorated work tends to go right through the leather, unlike the bottles where the colour is a surface coating. The most likely process involves stuffing the leather with a material that hardens it. There are a few historic references to the use of oils or wax. Waterer correctly rejects oils as these are softening agents. He is also suspicious of wax because he thought it principally as a waterproofing agent. Wax could be used to stuff the leather as it has a reasonably high melting point (60 degrees C.) and it makes it stable at room temperature, and hardens the leather somewhat. However, this work is in fact harder than wax could make it. Stearic acid could be the hardening agent here. Of the acids derived from animal fats it has the longest molecular chain and this means that in the solid state it would be the hardest. It has a high melting point (it must be heated to 70 to 80 degrees C.) and so would maintain hardness at normal temperatures. The leather is immersed in the stearic acid, heated sufficiently to be in the liquid state. The leather must be thoroughly dry during this stuffing operation so the high temperature will not affect the its structure. The stearic acid gives leather the characteristic black colour shifting to brown when less of the material is present. This corresponds to what we see in this category of objects. Pine resin (pitch) is also a possibility.”

“More problematic is how the surface decoration was accomplished. Gall (former director of the Deutsches Ledermuseum) suggests that the decoration was done in the usual way by wetting and then stamping etc. before any hardening.”

“White stuffing that was used for sophisticated repoussé (areas within the decoration were raised by packing a pocket in the leather with thread or similar material inserted through an awl hole hidden in anincised line).”

“Stearic acid makes the leather water resistant. It seems likely that the leather would have to have been heated to soften it sufficiently for carving, tooling etc. if in fact the decoration and forming came after immersion in stearic acid. Such working methods, if correct, are lost.”

“The earliest examples of leather drinking vessels date back to about the 13th or 14th century and the highly decorated scroll cases, missal cases, powder flasks etc. that remain only date back to approximately the 12th century with most being much more recent. These objects probably represent the end of a history that goes back much further.”

I found a picture of an ornately tooled Sword Scabbard (https://www.flickr.com/photos/andrea_carloni/4215963536) that belonged to Cesare Borgia (Italy, 1475-1507), but was never completed. 

“The back of the scabbard is decorated with 'CESAR' monograms and clusters of flames, his personal emblem, and the front with scenes of the worship of the Goddess of Peace. The modelled leather is thought to have been first moistened, then worked on in one small area at a time, and finally hardened with specially heated tools. It was never completed, probably because of the splits that occured on the reverse side.”

I want to find more items along this vein, but I am finding searching museum sites with translations from Google translate to be unfruitful (the translation function on many sites does not extend to keyword searches in their collection databases). I have previously been told by multiple individuals that leather tooling of this sculpted nature did not occur within period and therefore, should not be included on SCA recreations. 

I have found multiple examples where a very thin leather has been adhered to a carved wooden surface, which lends to a similar approximate result, but is not nearly so detailed and ends up looking cartoonish.

But then I have also found leather panels that have been worked similarly to repoussé.

1) The Allegory of Music (Northern France, 1570–1590) shows leather than has been blind stamped, embossed, molded and incised (https://www.metmuseum.org/art/collection/search/231781). It was only later installed on a wooden mount. The wood is not integral to the shape of the leather. 

”To create this panel three leather sheets decorated in the cuir bouilli technique, whereby the wet leather was manipulated and molded into the desired shape, were joined together. After the material was hardened and dry, the ornamental details were incised and punched into the surface.”

2) Panel featuring a Satyr (origin unknown, North European, 1530-1550) with embossed and gilded leather (http://m.vam.ac.uk/item/O331596/panel-unknown/). This item references an object in the British Museum for comparison, but no images is available in their online catalog (https://www.britishmuseum.org/collection/object/H_1881-0802-18). However, it sounds beautiful. 

“Panel of embossed leather; with an arabesque pilaster of early Renaissance style consisting of vases, scrolls, cornucopiae, birds, dolphins etc and terminating in an incense burner from which flames are issuing.)

3) Panel with Dolphins (Italy, 1450-1600) “stamped in relief with a vase with a handle on either side in the form of a leaf ornament endining in a dolphin's head. All these ornaments are gilt. The very thick leather is mounted with iron nails on a wooden board of the same shape” (http://m.vam.ac.uk/item/O370942/panel-unknown/).

4)  Panel with Grotesque Mask (Italy, 1450-1600) “stamped in relief with a grotesque mask and leaf ornament. Both these ornaments are gilt. The very thick leather is mounted with iron nails on a wooden board of the same shape” (http://m.vam.ac.uk/item/O370943/panel-unknown/).

5) Another Panel with Grotesque Mask (Italy, 1450-1600) (http://m.vam.ac.uk/item/O370870/panel-unknown/).

6) Parade Shield (Italy, mid-16th century) “Round shields like this example were used in pageants and parades throughout the cities of Italy, and the earliest surviving examples date from about 1500. From about 1450 or earlier, religious cavalcades and ceremonial entries into cities were modelled on Ancient Roman triumphal processions, and mythological and historical subjects were thought suitable subjects for the shields used in such parades. This example is decorated with Roman soldiers and classical grotesques (arabesque motifs with fanciful figures). It is made of cuir bouilli, a technique which involves moistening one small area of leather at a time and then working it with specially heated implements to create relief decoration.

Embossed and tooled cuir bouilli leather, decorated with classical motifs and a central octagonal panel depicting three Romans; a general in the centre flanked by two soldiers. A deep border contains figures of Mars, Hercules and Victory, with Cupids fighting interspersed with arabesques” (http://m.vam.ac.uk/item/O93199/parade-shield-unknown/).

The description of this Parade Shield makes me hopeful that I will find others of it’s ilk. So far I have only found other ornate ones backed with leather, but I will keep looking.

[EDIT: I have already found others thanks to The Wallace Collection.] 

7) Parade Shield (https://wallacelive.wallacecollection.org:443/eMP/eMuseumPlus?service=ExternalInterface&module=collection&objectId=60802&viewType=detailView), 

8) Parade Shield (https://wallacelive.wallacecollection.org:443/eMP/eMuseumPlus?service=ExternalInterface&module=collection&objectId=60803&viewType=detailView), 

9) Parade Shield (https://wallacelive.wallacecollection.org:443/eMP/eMuseumPlus?service=ExternalInterface&module=collection&objectId=60801&viewType=detailView), 

10) Parade Shield (https://www.pinterest.ca/pin/386324474288858620/)

The other examples of tooled leather panels I have found are from just out of period including three Crucifixion panels (https://www.britishmuseum.org/collection/object/H_1868-0627-4), (http://m.vam.ac.uk/item/O128148/leather-panel-de-rijsende-son/), and (http://m.vam.ac.uk/item/O119912/panel-heuvel-willem-van/). And multiple ornate wall hangings (https://www.pinterest.ca/pin/386324474288684608/), (http://m.vam.ac.uk/item/O370332/set-of-leather-heuvel-martinus-van/), and (http://m.vam.ac.uk/item/O369594/panel-unknown/), which seemed to come into fashion during the mid-17th century.