BPG Use of Leather in Book Conservation

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This page covers the use of leather and leather substitutes as repair material in book conservation. It was originally based on the summary write-up from "Pre-Meeting Symposium: The Current Use of Leather in Book Conservation" which took place May 29th, 2018 in Houston, TX prior to the 46th AIC Annual Meeting. Henry Hebert and Marieka Kaye moderated that symposium and authored the proceedings published in the Book and Paper Group Annual 37 (Hebert Kaye 2018). 
This page is intended to grow and develop from the original presentation. It differs from the published version by incorporating additional information from the original presenters. We also welcome the addition of other essays on the topic of leather in conservation. Please get in touch with the compiler at bookandpapergroup.wiki@gmail.com.
The BPG Wiki pages on Board Reattachment and Animal Skin and Leather are relevant to this topic.
Wiki Compilers: Katherine Kelly
Wiki Contributors: Emilie Demers, Ségolène Girard, Henry Hebert, Marieka Kaye, Katherine Kelly, David Lanning, Dan Paterson, Jim Thurn, Kristi Wright, your name could be here
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==Introduction to Symposium Henry Hebert, Marieka Kaye==
When confronted with the treatment of a damaged leather binding, conservators have many choices about which materials to use. The traditional approach is to repair “like with like,” selecting a tanned skin of the appropriate animal and dyeing it to match. In the past 20 years, many techniques that make use of alternative materials such as paper or cast acrylic media have been described in the conservation literature. With so many options available, how are conservators choosing which materials to employ?
This symposium offered an opportunity for wider dialogue about the materials used to repair leather bindings and a chance to ask questions or relate lessons learned at the bench. Speakers presented on all aspects of this material, from manufacturing, evaluation of “vintage” repair techniques, decision-making, and use of new materials.
Henry Hebert, Conservator for Special Collections, Duke University Durham, NC
Marieka Kaye, Head of Conservation & Book Repair, University of Michigan Ann Arbor, MI
==A Virtual Tour of the J Hewit & Sons Tanner and the Leather Manufacturing Process David Lanning==
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J Hewit & Sons has been in business for over 200 years, producing leather from goat, calf, and sheep skins. Many of the skins are sourced outside the United Kingdom, from Scandinavia, New Zealand, or the Indian subcontinent. Skins arrive at J Hewit & Sons in one of three different states: wetsalted, pickled, or native tanned. 
Animal skins are made up of many layers of tissue, containing hair and glands for the secretion of oils and sweat. The leather manufacturing process involves several steps to remove or alter these components prior to tanning, including washing in large drums, liming with sodium sulfide or hydrosulphide to remove hair and inter-fiber proteins, and mechanically defleshing to promote penetration of chemicals. 
There are many different types of tanning agents, including vegetable, mineral, aldehydes, and synthetic. These tannins can be used alone or in combination. Good quality bookbinding leathers should be vegetable tanned with slower acting pyrogallol tans. J Hewit & Sons predominantly uses sumac and tara tannins.
After sorting by quality, the leathers may go through several steps to be finished. They are first wet shaved to an appropriate thickness and then dyed in drums. At the same time, the skins may also undergo retanning, archival tanning with aluminum, or fat liquoring to replace lost oils. After drying, skins may be sprayed with additional dye or pigment, glazed, pressed, or embossed with a false grain using a large hydraulic press as a final finishing step. . 
Throughout the presentation, videos and images of each of these processes were shown. The videos are available on the J. Hewit & Sons website, and additional details of the leather manufacturing process are available through J Hewit & Son’s biannual newsletter, Skin Deep. In particular, the "Development of Archival Leathers" (Barlee 2017) and the "The Manufacture of Leather" series (Lanning et. al. 1996-2000) are recommended.
Q: Have you seen any trends recently in the use of your leathers? Are conservators buying less?
Lanning: There has been a lot more demand for our archival, aluminum retanned leather recently. Business is steady, though. The Managing Director’s son is currently studying chemistry and intends to follow in his father’s footsteps.
Q: Have you done any fold endurance testing?
Lanning: Yes. The Craft Project carried out 10 years ago included many specialized leather testing techniques, which had a big impact on our processes. The aluminum retannage that Hewit’s is using now was influenced by this study and the report can be found on our website (Barlee 2014).
Q: Why isn’t sheepskin a good bookbinding leather?
Lanning: The naturally high fat content in sheepskin creates voids with its removal during processing and it is prone to tear or delaminate. The climate actually has a big effect on the animal whilst it is alive, so Hewit’s is acquiring sheepskins from warmer climates. But it still isn’t recommended for durable bookbinding leather.
Q: You mentioned that a lot of the machines that you use are quite old. Are machines like those still manufactured?
Lanning: Most of our machines are well over 70 years old! Today, there are companies in China, India, and Italy that manufacture tannery equipment.
Q: Is there a detrimental effect of the alcohol in consolidant recipes? It appears to be pulling the moisture out of the skin and maybe that is making the problem worse. Isopropyl alcohol appears to be moving the dyes less than ethanol, so maybe it’s the lesser of two evils.
Lanning: Yes, that is true. In fact, we recommend against the use of spirit-based dyes for that very reason. Traditionally, we would try to rehydrate the skins with some sort of oil, but I know that is a point of contention among conservators.
Sarah Reidell: There has been a lot of great research about the effects of consolidants in AIC posters recently (Mahony and Pearlstein 2014; Knight 2016). SC6000 has waxy components that don’t age well. Cellugel is at least hydroxypropylcellulose but contains an added fragrance. I suggest just making it yourself, rather than purchasing it.
Q: I have some naturally aged skins in my personal collection and some are terribly degraded. Do you think that is due to the tannage used? Or other factors? Also, do you have naturally aged skins at Hewit’s?
Lanning: Dye can obscure evidence of the type of tannage used. With an undyed skin, you can often see discoloration along the edges from oxidation, if the skin has been tanned with catechol (poor quality) tans. Hewit’s has some naturally aged skins at least 80 years old.
Q: Have there been changes in the processing or manufacture of alum-tawed skins in the last 30 years? Some older skins that we have in our lab tear very easily.
Lanning: There shouldn’t have been a significant change in manufacturing, but alum-tawed skins do need to be conditioned if it is very dry in your space. You may want to humidify them a bit and see if there is a change.
David Lanning, Sales and Marketing Director, J Hewit & Sons, Ltd
==A Brief History of (a) Time: Reflections on 53 Years of Leather Conservation at the Boston Athenaeum Dawn Walus==
Founded in 1807, the Boston Athenaeum is one of the oldest independent libraries and cultural institutions in the United States. The collection contains books, paintings, sculpture, works on paper, and decorative arts. The history of conservation at the institution can be described in two major periods: 1807–1962, “before conservation,” and 1963–present. Before the establishment of a conservation program, many books were sent to commercial binders for binding and rebinding, often in half or quarter leather with decorative paper over boards. The building did not see proper environmental controls until the last renovation in 2003, so the collections were regularly exposed to excessive heat, air pollution, and coal dust from the heating system, which probably contributed to the deterioration of collections. 
In the 1950s, a former elevator operator was put to work applying a product called Liquick Leather to damaged or deteriorated leather bindings. Liquick Leather is a scientifically formulated plastic designed to retain its flexibility for many years. The instructions suggest cleaning the binding before application with carbon tetrachloride, a substance with known toxic effects. The product was applied to leatherbound books, as well as parchment and cloth bindings. It was usually applied only to the spine and was sometimes toned. Today, the coating is often brittle and occasionally adjacent Liquick-treated books stick together. Images of books with Liquick Leather coatings from the circulating and special collections were shown.
The first conservator at the athenaeum, George M. Cunha, made major changes. Discrete collections were prioritized for treatment with a new emphasis on more thoughtful repairs. One of the first priorities was the King’s Chapel collection. It is the oldest colonial library in Boston and features 17th-century theological works bound in leather. An image of the only incunabula in the collection was shown. It had been rebound in 1821 in a style more appropriate for the 19th century than the 15th century, and rebacked sometime prior to 1963. Of the treatment, Cunha writes, “I have never seen a better example of butchery on such a costly book.” This serves as evidence of a shift from rebinding as repair to a more intentional approach, with consideration of the binding and its significance. For the highest value materials, Cunha tipped descriptions of the treatment inside the back of the book. A common treatment of the time was to clean and treat leather bindings with castile soap, potassium lactate, and British Museum leather dressing. Cunha experimented with accelerated decay testing of leathers available at the time, and those samples still exist.
In the modern era, treatment decisions are made more selectively. During the presentation, several recent treatments, including rebacking in leather, rebacking with toned Japanese or Korean tissues, and full rebinding in leather were discussed.
Former von Clemm Fellow Lauren Calcote conducted research on the identification and removal of Liquick Leather. Using FTIR, the product was identified as polyvinyl acetate (PVA) and was successfully reversed with acetone, except in cases where the leather was severely deteriorated (Calcote 2016). Associate Conservator Evan Knight compared the visual effects of Klucel-G in various solvents at various concentrations as well as application by brush and by spray (Knight 2016). A solution of Klucel-G in isopropanol is the current protocol for leather consolidation. 
A recent shelf-cleaning project on a collection of large leather volumes was also described. The bindings were covered in dust and soot and the leather was flaking and powdery. The cleaning was undertaken after learning of a staff member’s allergies, which worsened after working in close proximity to the collections. Since treatment, the staff member reported that the allergy symptoms have not returned. This serves as a reminder that the materials we work with can cause harm and that small-scale efforts can make a difference. 
Q: Is Liquick Leather still produced?
Walus: Yes, but under different names. 
Q: Did Captain Cunha record notes in all or most of the books treated during his tenure? 
Walus: No, he just concentrated on the highest priority and valuable collections. There are lots of notes in those books, but most of it is very generic information. There are no specific notations about the source of materials, for example.
Dawn Walus, Chief Conservator of the Boston Athenaeum
==Understanding the Material Properties of Leather, Old and New William Minter, Katie Wagner, Kristi Wright, Holly Herro, Laura McNulty==
Leather is an ideal material for covering books and members of the book trade have been discussing the quality of leather since the early 19th century. A bookbinder determines quality from training, experience, and interaction with the product, but how do you identify the quality of the tannage? There was an anecdote that T. J. Cobden-Sanderson actually tasted leather to judge the acidity. For the modern conservator, however, simple testing may be possible using the equipment available in a standard conservation lab. A leather discussion group, consisting of the members of this panel, was formed 2 years ago to investigate questions about leather quality and use within the bookbinding and conservation community.
Historical tanning processes, from ancient to medieval, were described in the presentation, comparing the methods and materials used to the ones described in David Lanning’s presentation. Also included was an overview of scientific research into the mechanisms of leather degradation beginning in the 1800s, proceeding through the Printing Industries Research Association (PIRA) test (Plenderleith 1967), and followed by the establishment of production standards. Binders disliked the working properties of the early leathers produced adhering to the standards and, thus, the more recent STEP, Environment, and CRAFT Projects emerged in Europe, which aimed to improve those properties (Larsen, Vest, and Kejser 1994; Larsen 1996; Barlee 2014). 
Members of the panel have been conducting an ongoing survey on how bookbinders and conservators interact with leather. An email questionnaire was developed to ask how individuals select leather for purchase, what qualities they think contribute to longevity or workability, their preferred type of tanning, and if they have noticed changes in the quality of products available on the market. Some early results were described. Many survey participants select skins by color, grain, thickness, and workability. Binders would prefer to purchase leather made with specific tanning agents but would like samples of the material before buying. Responses from tanners indicated that they would be open to changing production methods if there were sufficient demand. 
The group has been performing tests in an attempt to correlate skin stability with the tanning process used. A number of modern and historic leather samples have been collected and are currently being tested for moldability, wettability, shrinkage temperature, pH, and response to a modified PIRA test. Additional testing efforts currently underway at the Smithsonian were also described, including how proteins are altered during tanning and insight into protein degradation over time. 
There are many other avenues of cross-disciplinary leather research with zoo archeologists or archaeological conservators, particularly since the breeding and diet of livestock has significant effects on the quality and thickness of the animal skin. The composition of herds and agricultural practices have changed significantly since colonial times.
Q: What size of sample is required for testing of the leather?
Minter: A set of five 2″ × 2″ squares has been required for our testing, but most labs that will do testing just need one square that size. Bigger sample sizes and a larger quantity of samples is of course better.
Q: Why are American conservators so “behind the ball” on research into leather?
Minter: Good question! It may be because, without naming names, a lot of institutions who have the resources to conduct research aren’t using leather in their treatments. 
Herro: The results from the questionnaires and discussions with longtime book conservators in the US suggest that there is little awareness of European efforts in testing and discussion of production standards.
Audience comment: Maybe research isn’t happening because there isn’t much of a leather trade in the US, and thus no need to preserve industry jobs. CCI has lost a number of scientists focused on proteinaceous materials in the last few years, but hopefully that will be turning around soon. 
William Minter, Senior Book Conservator, Pennsylvania State University Libraries
Katie Wagner, Rare Book Conservator, Smithsonian Libraries
Kristi Wright, Contract Book Conservator, National Library of Medicine
Holly Herro, Senior Conservator, National Library of Medicine
Laura McNulty, Pre-Program Conservation Volunteer, National Library of Medicine
==Love it or Hate it: Tanned Leather in Institutional Conservation Programs Compared to Private Practice James Reid-Cunningham==
Trends in the choice of material used to repair leather bindings have shifted in conservation labs serving cultural institutions. Leather was once the primary material used but, over time, library conservators began using Japanese paper almost exclusively as a repair material. Comparing private practice to working in an institution, very few clients are interested in minimal intervention; no one wants to just put their broken binding in a box. While the “less is more” approach is acceptable in a lab serving a research library, a client will typically adopt the opposite view. The private practice conservator must balance what the book needs and what the client wants, and often what the client wants is leather.
A great deal of the presentation focused on reversibility. The full method of preparing a leather-bound book for rebacking with new leather has many steps. The process is difficult and can be quite invasive to the original binding; however, one must ask the question, “Invasive compared to what?” Adding a Japanese paper repair adhered over the leather tends to fail by shearing off the grain layer of the original leather. While polyvinyl acetate (PVA) is commonly stigmatized due to nonreversibility, even water-soluble adhesives are nearly impossible to reverse without affecting the original leather, simply because of the amount of moisture required. In reality, few repairs to a leather binding are actually reversible.
Many of the leather rebacks that we encounter as conservators were completed by skilled binders apprenticed in the book trade, but some were done quickly to avoid the high cost of rebinding in leather. As a result, poor repairs were executed. But because a repair technique was executed poorly in the past, that does not necessarily mean that conservation professionals should give up on it. Great care can be taken to add structural components under the leather reback, including board reattachment or reinforcement through strong textile extended linings, rebuilding broken sewing supports, or board tacketing.
Many books may have no binding left or require a new binding. In those cases, rebinding in a period style requires using tanned leather because it was the most common covering material during many historical periods.
Models of training for professionals in the field have also dramatically changed. The historical model of training bookbinders included apprenticeships for many years. At present, book conservators have to learn many skills in a short period of time and, as a result, less time is spent on craft. Basic skills handling traditional materials appear to be on the decline. It may be that program-trained conservators tend to end up in institutional labs, while bench-trained conservators end up in private practice. 
Q: A lot of design bindings and artists’ books are bound with chrome-tanned leather. Should chrome-tanned leather be used to repair those bindings?
Reid-Cunningham: I’m not sure if there is a reason that a repair requires vegetable-tanned leather. It’s just easier to pare. The appearance of colors and surfaces of mineral-tanned skins are often very different than vegetable-tanned skins, so it could be appropriate to use in those cases.
Q: How do you manage the client’s expectations about how the finished treatment will look when repairing with an alternative material like Japanese paper?
Reid-Cunningham: I keep samples on hand to demonstrate how the repair will blend with the appearance of [the] original. Conservator Christian Scheidemann once said that the goal of conservation isn’t to make the object look new, the goal is to make it look like a healthy 40-year-old.
Q: Have you noticed a correlation between the better quality archival leathers and the difficulty of paring?
Reid-Cunningham: Newer archival skins are much easier to pare, cover, and tool than they used to be. The first aluminum-retanned leathers produced in the 1980s were very stretchy. 
James Reid-Cunningham, Cambridge, Massachusetts
==Materials Used for the Application of Japanese Paper Repairs in the Conservation of Leather Bound Books Emilie Demers==
Books have historical importance both in the text and the materials used for their construction. A binding can provide a great deal of information about the context of its production, such as the geographical location, the socioeconomic status of the owner, the bookbinder’s skill, and common binding practices for the period. Skills in preparing leather for bookbinding allow for a better comprehension of the materials and how they behave under various conditions, which is crucial in book conservation. Although the art of bookbinding and leather preparation is important and still considered in conservation, the large numbers of books in need of conservation treatment have spurred development of many new techniques to create strong and stable repairs that do not require the use of leather. Japanese paper, which is both cost effective and time efficient, has proved to be an effective substitute. As part of its use in a leather binding repair, Japanese paper may be coated with various materials to change the color, surface texture, or sheen. The effects that these coatings have on the physical strength of Japanese paper are unknown.
To investigate this question, a selection of materials were tested on Kurotani #3 Japanese paper from the Japanese Paper Place: Burnt Sienna Golden acrylic paint, Cellugel (hydroxypropylcellulose and isopropanol), SC6000 (emulsion of mixed waxes and acrylic polymers in aqueous isopropanol), and Jade 403 polyvinyl acetate. Samples were made with up to four of these layered coatings, applied by brush. 
To observe how these materials affect the physical strength of Japanese paper, a fold endurance test was performed. To test the viability of these coatings over time, two-thirds of the samples underwent up to two rounds of accelerated aging prior to fold endurance testing. One hundred twenty samples were adhered to board with Lascaux 498 adhesive and an ESPEC humidity cabinet LHL-112 was used to age them at 30°C and 65%RH for 18 days. Sixty of those samples were aged again at 35°C and 65%RH for 21 days. A Tinius Olsen model 4C012A tester was used to conduct the fold endurance test. 
The results from the fold endurance testing show that, without accelerated aging, each of these coatings increases fold endurance. After one round of aging, the strength of toned Japanese paper without additional coatings was increased, while the fold endurance of all other samples was reduced. After two rounds of aging, all the samples decrease in strength; however, the toned Japanese paper coated with Cellugel and SC6000 had close to the same strength as the unaged sample with the same coatings applied.
Emilie Demers, Graduate, Queen’s University
==Replicating Original Leather Surfaces with Textured Repairs Sarah Reidell==
Sarah Reidell and Grace Owen-Weiss co-created and published a technique for creating textured repair materials in the 2010 Library Collections Conservation Discussion Group (Haun and Beenk 2010, Owen and Reidell 2011). Now referred to as “textured fills,” these materials are composed of a thin layer of acrylic media and a repair substrate cast on a silicone mold bearing the negative pattern of a leather or textile surface that matches the original. This method has been successfully employed in the conservation treatment of bound volumes, cased photographs, and objects with leather or other textured components. 
Traditional treatment techniques for leather bindings, such as the leather reback, are often invasive. The degradation of modern leather can be influenced by a number of variables outside the conservator’s control, such as delays in the supply chain, manufacturing secrets, and changing formulas. Repairs with toned paper are not as durable and can be more difficult to aesthetically integrate with the original leather covering. Textured infill techniques developed for objects and paintings can be very successful, but often require the mold to be made directly on the object; this is not possible on degraded leather bindings. 
Commercially available, nontoxic, mold-making kits (such as Smooth-On Rebound 25 platinum-cure silicone rubber) can be used to create a negative grain pattern on leather surfaces. Sacrificial surrogate surfaces are recommended for creating the textured silicone rubber mold to avoid depositing oily residues on original objects. Molds of textures that match materials in your collection can be made and then reused repeatedly in your lab.
To create a textured fill, a mixture of acrylic paints and mediums, matched to the color and gloss of the original object, are cast onto the mold. A support layer of thin mulberry paper or similar repair substrate may be added to the back of the acrylic media. When dry, the newly combined acrylic and paper layer can be removed from the mold. This material can be made at low cost and with little training. It does not require hazardous solvents and is more flexible than texturing techniques using BEVA resin. 
Before applying a textured fill to a leather-bound volume, the book must be prepared by surface cleaning, consolidating degraded leather, and completing any internal structural repairs to stabilize the board attachment. The textured fill is an aesthetic compensation that can complement other primary stabilizing repairs. With this method, like many methods relying on paper or textile, the internal repair materials should be doing the work. 
When the book is ready to receive the textured fill, repairs can be prepared in a number of ways. The repair can be shaped by needle puncturing, tearing, cutting, or using a scalpel. Bulky edges can be sanded or pared from the verso to remove excess material and bevel the paper. Repairs can be adhered with either direct wet adhesives or indirect heat- or solvent-reactivated adhesives (Anderson and Reidell 2009). Indirect adhesive methods allow repair materials to be attached in stages, such as adhering over the boards and joints and then going back to complete the turn-ins. 
Matching color, sheen, and texture is important for creating a seamless repair; however, matching just two of those criteria can result in a successful aesthetic integration. Careful selection of transparency ratings on the acrylics allow layering of different colors on the silicone mold to create more vibrant and natural colors. Examples of textured fills on a sample binding and boards were distributed to the audience to demonstrate the effectiveness of different combinations that met only two of the criteria (color and sheen, color and texture, etc.) using the “3-ft. rule” of aesthetic compensation, according to which, a repair material matches the original when held at arm’s length but is acceptably visible at close distance. 
Textured fills are a fast and relatively simple substitute for leather as a surface integration layer for effective structural repairs in bound volumes. They can and should be a part of the wide variety of techniques conservators use to repair bound volumes and other objects with textured surfaces. They don’t replace more traditional leather techniques but give conservators a better ability to simply and quickly replicate complicated textures.
Q: Is it possible to cast the mold directly on the book?
Reidell: Yes, but it’s very risky! In our experiments, we were unhappy with an oily residue sometimes leftover from the silicone rubber. Caution suggests that surrogates are the best option for now. 
Audience comment: I have used a textured fill for a full reback, and experimented with textured fills on different supports, such as Aero Linen and Tyvek. I was able to apply it successfully, but it was stiffer than expected. In future attempts, I would make it thinner and more flexible, and change the number and layers of spine lining. 
Sarah Reidell, University of Pennsylvania Libraries
==SINTEVA Cuirs: An Alternative to Current Materials for Leather Loss Infills Ségolène Girard==
300px|thumb|right|Sample of SINTEVA.
The disciplines of conservator and craftsperson are intertwined and difficult to separate, as the first restorers of leather bindings were bookbinders. There are many difficulties in working with leather, including unknown materials used in the tanning process, dye bleeding during wetting and covering, hydrolysis and oxidation of the leather, as well as the irreversibility and invasiveness of the traditional method of the leather reback. It is hoped that European conservators were often more likely to choose alum tawed skin or Japanese paper as a repair material than tanned leather. But even if they are suitable repairs in many cases, drawbacks met in those alternatives led us to investigate a new material for leather bindings repairs.
BEVA 371 is often used for the conservation of paintings, developed as an alternative for wax consolidants. Analysis of BEVA has been conducted by the Canadian Conservation Institute (Down et al 1996) to find a repair material for leather in ethnographic collection. Reassessment of repairs to leather with BEVA have shown positive results (Kronthal et al 2003) in the long term. However, if BEVA is compatible with leather, it could not be safely applied to a leather binding with heat, as it activates at a higher temperature than the skin denatures.
SINTEVA is a new alternative to leather in development, composed of BEVA 371, glass microspheres, and raw pigment. A multi-step process is used to create textured material. The solution is heated and brushed onto both a sacrificial leather surface and a stretched canvas. The stretched canvas is pressed onto the leather, sandwiching the BEVA mixture between leather and textile, and heat is applied to the verso of the canvas to fully join the two layers. When the mixture has dried and cured, it can be peeled away from the sacrificial leather and the print remains on the textile support. This method captures a negative impression of the leather surface, but the texture is easily visually integrated with leather. The material can be cut to shape and pared like leather, and adhered with wheat starch paste thanks to both the canvas lining and the glass microsphere addition. Experiments are currently ongoing to evaluate the addition of glass microspheres as a bulking agent and to ease the printing process.
Tensile-strength testing of SINTEVA has been conducted, comparing unbacked SINTEVA to Tengujo (30 gsm) Japanese paper. Strips of SINTEVA and Japanese paper were adhered to the face of a leather-covered board. The SINTEVA strips failed under less force than the Japanese paper (16 Newtons average), but did not break at the site of adhesion. By comparison, the Japanese paper failed at 56 Newtons (on average), but tended to tear away the grain layer of the leather. Under tensile double-fold endurance testing, SINTEVA outperformed Japanese paper by approximately ten to one, on average.
Creating a leather alternative from BEVA is difficult and can be hazardous for conservators outside of a lab setting. Commercial production of SINTEVA is currently being pursued to offer the finished material for sale. Samples of SINTEVA are available upon request.
Q: Can you clarify the reason for using microsphere fillers with BEVA? Are the microspheres also functioning as a bulking agent? Are they able to flex across the joint?
Girard: Yes, the microspheres are for bulk and adhesion. The BEVA will obviously not adhere with paste, so you need to add fillers in order for it to adhere with the usual rice or wheat starch adhesives. They work both for areas of infill on the board and for joint repairs. They make the repair quite stiff, so maybe for better flexibility in repairs across the joint, SINTEVA infills would need to be shaped in a 90° angle before use instead of being flat.
Q: Have you considered using cellulose powder as a bulking agent?
Girard: Not yet, but it definitely sounds like an idea worth investigating. It would enhance SINTEVA flexibility and light-weight that can be lost with the addition of glass microspheres, with the same ability to adhere with pastes.
Note: additional information will be printed in an upcoming Journal of Paper Conservation article (Girard 2018).
Ségolène Girard, Conservator in Private Practice, Versailles, France
==The FULL TOOLKIT Approach to Leather Repair at the Library of Congress==
===A Review of Past Treatments to Leather Bindings at the Library of Congress Dan Paterson===
The pre-conference symposium Use of Leather in Book Conservation provided context for reviewing past treatments with a focus on the materials used and their performance over time. Head of Book Conservation at the Library of Congress, Shelly Smith, and I selected treated volumes by going through documentation files from 1984-2003. The treatments selected for review came from the Rare Book and Special Collections Division at the Library of Congress which has been part of an active treatment program since the creation of the Library of Congress Conservation Division in 1971. I reviewed each of the selected items using a checklist to evaluate the same criteria. 
Selection of Items for Review
Thomas Jefferson’s library is a discreet collection within the Rare Book and Special Collections Division. Because of its importance to the history of the Library of Congress Jefferson’s library has received a significant amount of treatment over the years. Based on anecdotal knowledge shared by former and current staff members we anticipated a wide variety of techniques to repair or stabilize leather could be evaluated. Also, the collection has been displayed in its entirety, first in 2000 to mark the bi-centennial of the Library of Congress, and again in 2008 as a permanent display to illustrate the influence Jefferson had on the Library and the nation. Thus all of the treatments that were selected for review have been part of the exhibition and on view for the past eleven years and been subjected to the additional strain of display.
Problems, however, with focusing solely on Jefferson items caused the scope of the review to be expanded and include items from other collections. For example, all of the conservation treatment reports for Jefferson items use the LC call number classification as the identifier. Since the exhibit in 2000 however the collection has been shelved as Jefferson envisioned and is no longer organized by LC classification. Additionally, the display cases must be opened by two people and the retrieval process is somewhat laborious. During review of documentation we initially selected 30 titles for examination. However, given the amount of work required by Rare Book staff to assist in the process of first correctly identifying the book and then retrieving it, selection was expanded to focus on material from other collections within the Rare Book Division that could be more easily accessed. Seventeen additional titles were chosen from the treatment documentation files spanning the years from 1984 to 2003.
Type of Treatments Reviewed
Because of the focus of the symposium treatments selected for review fell into two main categories: repairs to existing historic leather bindings, meaning, in most cases board reattachment, or new leather bindings created to replace a failed or compromised binding structure. Within the board reattachment category there were records of four different materials utilized as the primary repair material: leather, paper, linen, and Tyvek. All new leather bindings were completed with either calf or goat skin.
Methodology
After the 47 volumes were selected I created a simple checklist form to evaluate all of the treatments. The form was used to record the treatment performed and the year. The checklist also included several types of degradation that were anticipated, such as acidic migration from new leather onto pastedowns, endsheets and gutters, loss of grain layer of new leather, and damage caused by incompatible repair materials on weaker historic bindings and textblocks. Finally, each book was assigned a number on a scale of 1 to 5 to evaluate the current stability and success of the repair. 1 represented books with treatments that had completely failed and 5 represented treatments that were completely stable.
Examination Results: Leather
Of the 47 books examined, 32 utilized leather as the primary repair material, either for re-backing or as a new binding. Somewhat surprisingly, none of the 32 bindings was graded below 3 on the scale of 1-5, meaning none of them appeared unstable or in need of new treatment in the foreseeable future. The average score was 4.2. The most common problem, observed on 5 of the 32 volumes, was darkening of the pastedown over the turn-in, suggesting migration of by-products in the new leather. The earliest example appeared on volume treated in 1984 and the most recent example is from 1999. This problem was minor in most cases, causing limited discoloration of the pastedown but no chipping or cracking, as is often observed in historic examples of this problem. There were also no indications yet of transfer to the conjugate endpaper. Interestingly it was observed only on new leather bindings as opposed to being on a mixture of re-backs and new leather bindings. The most likely explanation is that virtually all of the re-backs examined had a transverse linen spine lining inserted under the pastedown, providing an extra layer between the repair leather and the pastedown. This step appears to have been a regular part of the re-backing protocol to reinforce the joint repair from at least 1984 onward.
Other less common problems observed were light damage of leather dyed to match original historic leather (noticeable on 3 volumes) and early signs of flaking of the grain layer (1 volume).
Perhaps the most common issue related more to the functionality of some of the treatments, a separate concern from the stability of the leather. A number of examined volumes had constricted openings that did not allow for the text pages to drape naturally. This problem is complex and is not always related solely to the material used for the repair. It is often the result of a number of factors and the material used for the repair is just one of them. Still there where a number of volumes examined that may have functioned better if a more relaxed opening were achieved through allowing more flexibility to the spine than was afforded by re-backing in a tight back style. 
Paper
Eleven bindings utilized paper as the primary repair material. The average score assigned to them on the 1 to 5 scale was 3.4. The lower score, as compared to leather, is influenced in part by two bindings. Of these, one repair only utilized interior hinges made of Japanese paper. The other had an interior hinge and an exterior paper repair attached to the outside of the leather on the spine and the board but the repair paper has begun to separate from the leather. Both repairs were failing from a structural standpoint, leaving the boards nearly detached once again. Additionally, they had not addressed problems to the caps and flaking spine leather which presumably were not as bad when the books were treated in 1990 and 2000 respectively. 
While I observed only two of these more simplified approaches during the survey these observations are echoed by Tamara Ohanyan, book conservator for digital projects at the Library of Congress. Ohanyan is in the process of reviewing Jefferson collection items prior to scanning and has encountered a significant number of repairs done on the exterior of the leather. The repairs were mostly done prior to the first Jefferson exhibit in the year 2000 as a way prepping the collection for display. Ohanyan estimates that 50 percent of this type of repair is showing at least the initial signs of failure by lifting away from the spine edge. 
The other 9 treatments that utilized paper as the primary repair material were functioning much better. The majority were done as paper re-backs where the spine and board leather were lifted and the repair material inserted underneath. Interestingly, a number of these volumes also had very restrictive openings. It was not always possible to determine the kind of paper used for the repair based on the treatment reports. The lack of open-ability however, is due presumably to a heavy application of acrylics, adhesive, and tight back structure that created significant rigidity on the spine, just as new leather would likely have done. 
Tyvek and Linen
Two of the treatments reviewed relied on Tyvek as the primary repair material, one from 1986 and one from 1994. Presumably the scarcity of Tyvek treatment stems from the experimental nature of relying on polyester as material for board reattachment but based on this very tiny sample both repairs are still functioning well. The repair from 1986 (graded as a 5) was inserted under the spine, across the joint, then under the pastedown. The repair from 1990 (graded as a 4) was only on the inside of the book, from the pastedown across the joint and inserted under the pastedown. It had a noticeably better, more robust feel to it than the paper repair described in the previous section that was similarly on the inside of a volume. 
One noticeable problem was that the acrylic used to tone the repair did not seem permanently affixed to the Tyvek, causing some loss of the media though the overall effect was minor. 
Two treatments, one from 1986 and the other from 1990, utilized linen as the primary repair material for board attachment. In both cases the leather was lifted and linen inserted underneath. Both repairs are still functioning and graded high for appearance and stability. In particular, both treatments had the linen well-integrated visually with the leather which is often difficult to achieve given the regular pattern of the weave compared to the irregular pattern of natural grained leathers.
Conclusions
Given the limited sample size of 47 treatments it is difficult and to draw firm convictions on the efficacy of any of the repair materials examined. More importantly, it’s not useful to compare them against each other as a means of establishing a dominant approach. The most obvious conclusion that I feel I can safely make is that repairs that are attached to the leather on the exterior of the binding are most likely short term and have a higher percentage of failure. A repair that can be inserted under spine leather, regardless of the repair material used, has a much higher likelihood of long-term stability. How to balance that long-term stability with the greater difficulty, invasiveness, and risk to the object of going under the leather is also part of the conversation that should be undertaken when considering treatment options.
===Board Slotting and Laser Printed Kozo Jim Thurn, presented by Katherine Kelly===
One of the techniques described in the Library of Congress panel discussion was a combination of board slotting and spine replacement with laser printed kozo on a large collection of 18th and 19th century American Statutory Law volumes held by LOC’s Law Library. Approximately 1300 books required substantial treatment. Nearly all of the volumes are in non-original bindings, having been bound in half leather with cloth sides by the Government Printing Office in the 1920s to 1940s. The Statutes are relatively brief, resulting in thin volumes that for the most part are less than ½ inch thick. The red, brown, or tan leather, mostly calf, is poor quality, and the endleaves are terribly acidic. The text blocks, however, are mostly stable, made of good quality paper, and require little attention.
The treatment strategy needed to address the problems and meet the needs of the division, hopefully without occupying conservators and technicians for years to the exclusion of the other worthwhile projects from the Law Library. According to the liaison to the division, the volumes are regularly (though not frequently) consulted by patrons, and are on a list of possible future digitization projects.
The board slotting technique is similar to others described elsewhere, using a Peachey board slotting machine and hinging material made of a laminate of airplane cotton and Korean kozo paper. The spines of the volumes are very thin and the leather very degraded, making reuse of spine pieces or labels impossible. Board slotting was a good choice for this collection because it does not disturb the fragile leather.
File:PrintedKozo1.jpg
File:PrintedKozo2.jpg
File:PrintedKozo4.png
The templates above illustrate the production of spine labels. Photoshop is used to create custom measured, colored, and labeled strips that cover the exposed spine and joints and recreate the original label, either vertically or horizontally. The spine pieces are printed using a LaserJet printer and inks on Korean kozo paper. These books are organized by state and year. Because there are so many of them and with limited shelf space, the division did not want boxes. So, it is a great solution to be able to print the labels on the spine.
To streamline the work in Photoshop, color palette templates of the most frequently encountered colors of leather in the collection were created. One simply matches the color of leather to the template, set the spine width, enter the title, and print directly onto the kozo paper. New technicians and interns are routinely taught these treatment procedures, and they use these palettes to select the most appropriate template to print their repair material. 
:Treatment Steps (see full details in the Thurn 2018 pdf below):
:# New endpapers hinged on.
:# Spine lined with overhanging cloth-kozo laminate.
:# One-on, two-off hollow tube, made with kozo
:# Overhanging printed kozo spine piece
:# Boards slotted with Peachey board slotting machine
:# The spine lining and the spine piece are both adhered into slots in the boards.
:# Corners are also reinforced as necessary
:# No boxes, just Mylar wrapper
===Leather Rebacking Katherine Kelly===
Another technique used at the Library of Congress and many other institutions is leather rebacking. This technique was recently used to repair volumes from the 3rd edition of Diderot’s Encyclopédie printed in the 1770s. The set consists of 33 volumes from the Rare Book and Special Collections Division and is frequently used in teaching at the library.
Physical Nature: These are large thick volumes, all in original bindings. Boards attached with recessed cord supports under thin leather. Tightback leather with intricate blind and gold tooling
Factors in Deterioration: Heavy use. The repeated stress of opening acts on the joints, which consist of thin leather, sewing supports, and endpapers, all of which have deteriorated with time.
Current Condition: This has resulted in the front and back boards becoming detached from all 33 volumes. Although the sewing is uniformly sound, the text blocks are now at risk of increased damage under continuing use.
Treatment goals: Return the volumes to safe, functional order while retaining the beauty and historical evidence of the original binding.
Risks of treatment: Loss of spine material due to thin leather and lots of heavy-handed tooling. It is also difficult to lift spine leather near the curve of the shoulder. Darkening of original leather due to adhesive on facing tissue and adhesive used to readhere original leather. Despite that, the justification for treatment was strong – essentially, the benefits of treatment to the entire run far out-weigh the associated risks.
Treatment Protocol: Leather reback with overhanging cloth lining. This provides the look and feel of leather (for which there is no real replacement), but unlike the original binding structure, we are not relying on the leather for board attachment. Leather was also used for to rebuild the corners, but toned kozo was used to patch up the exposed board edges.
:Treatment Steps:
:#Consolidate friable leather with Klucel G in ethanol
:#Face spine with RK-0 tissue precoated with ethanol-reactivated adhesive.
:#Clean and reline spine with kozo tissue, overhanging bias-cut aerolinen lining, reinforced by sewing through, handmade western paper, and a 1-on-2-off hollow tube.
:#Reattach boards with overhanging cloth underneath lifted pastedowns
:#Reback with new calf-skin leather underneath lifted board leather. Toned with BASF leather dyes in isopropanol.
:#Hinges cosmetically filled with kozo paper digitally printed with the marbled paper pattern.
:#Reattach spine piece with PVAc and remove facing.
:#Corners rebuilt and covered with leather. Exposed board edges filled in with toned tissue.
Evaluation 2 years later: A conservator evaluated the treatments 2 years later and after the volume had been used several times. The only problem was the toned tissue. There were a few areas where abrasion had caused the edges of the tissue to lift. Where the tissue went under the leather or butted up against it, it was fine, but where it extended over the old leather, there was a tendency to lift. The leather on spine and the boards was still well attached, and the book opened well.
===Spun Polyester Repairs Dan Paterson===
 	
Front board detached 	Broken inner hinge before repair
 	
Board reattached with polyester and paper laminate and textured fill	Inner hinge after the printed marble pattern hinge is fully attached
A third technique employed at the Library of Congress are repairs that utilize spun polyester for books with degraded leather or vellum over the joints. These techniques have been done on a limited basis but have been successful in each instance. The main criteria for selecting spun polyester are the characteristics and limitations of the original leather. Volumes that were bound in leather that was pared extremely thin over the joint often end up with detached boards. The thinness of the leather complicates the process of repairs due not only to the difficulty of lifting degraded original material but also due to the difficulty of finding a thin, durable repair medium that can be incorporated unobtrusively into the joint and be visually sympathetic. 
Spun polyester is significantly thinner than airplane linen and most Japanese and Korean papers. As a reference, the Tengujo paper used at the Library of Congress measures between .003-.004 mm and the Hollytex brand spun polyester used for the repairs pictured below measures between .004-.006 mm. The spun polyester also takes acrylics well and can be easily toned to match the original leather or vellum. Because of its shear nature it is usually laminated to a thin support paper (also toned) to give it opacity. The paper layer is often easier to attach to board and spine linings. 
The thinness of the repair material can also be a positive asset in regards to lifting. Unlike a leather reback that requires significant lifting, this repair can often be done with less lifting since it requires no paring and can manipulated into the desired location easily.
When ready to be applied to the object, the repair laminate will be a similar thickness to a medium or heavy weight Japanese or Korean paper but with greater resistance to tearing 1 and often a better match visually than using paper alone. It can also be used in conjunction with the textured repair methodology described by Sarah Reidell, providing the strength and durability for the repair and a support for the textured fill. 
File:Spun-Polyester-Repair-03.jpg|Sections of a polyester and paper laminate inserted under vellum for spine repair
File:Spun-Polyester-Repair-04.jpg|Sections of a polyester and paper laminate inserted under vellum for spine repair
File:Spun-Polyester-Repair-05.jpg|Completed repair
:Treatment steps follow this general order but are modified based on the limitations and needs of the object:
:#If the inner joint is broken, a new hinge is made from long-fibered Asian paper. If the original endsheets have a pattern or are marbled an image of the pattern may be printed on the hinging material for a better match 2. The hinge is only attached to the shoulder at this point so the board is still loose or unattached during the repair. Leaving the board unattached makes it easier to work with and having the hinge in place facilitates the correct positioning of the board at the time of attachment. 
:#Leather or vellum is lifted off the spine and the board. Lifting often does not require the entire spine be exposed, only portions to allow for the attachment of the repair material.
:#Spun polyester is toned with acrylic. This step is usually done by placing the polyester on Mylar and brushing out the acrylic. 
:#Support paper is toned, if desired. The choice of paper varies but it is usually a light to medium weight kozo paper.
:#Polyester and paper are laminated together, usually with a mixture of 1:1 paste, PVAc and dried under pressure between press boards. It is helpful to let the repair piece air dry for a minute or two so that it is not too tacky when being put into the pressing package. 
:#The repair material is attached to the object, usually with paste and a small amount of PVAc. For calf skin and vellum repairs the spun polyester is often a good match for the surface characteristics of the animal skin. For goat and sheep the addition of the textured repair makes for a visually sympathetic finish. 
:#Original leather is put back down with paste, a paste/PVAc mix, or Lascaux depending on the needs of the original material. 
:#The remainder of the hinge is put down on the inner face of the board with wheat starch paste.
:1The tear resistance comparison between polyester/paper laminates and paper repairs has only been done informally. It should be mentioned that airplane cotton or linen both have significantly higher tear resistance than polyester or paper and emphasized that the polyester repair is only recommended for objects where a cloth hinging material is difficult to sympathetically incorporate.
:2 See Jim Thurn’s handout for more detailed information on the methods for printing directly onto Asian papers used at the Library of Congress (Thurn 2018).
===The Full Toolkit Approach Shelly Smith===
The questions posed in the call for papers for this symposium were provocative. Why should conservators need to choose between leather and alternatives like Japanese paper? Why not use both? There is no perfect treatment; options can be chosen to prioritize cost, time, or other factors. This panel discussed a full toolkit through case studies of past treatments. They described the thought process behind the treatment decisions and evaluated the success of the repair after several decades of aging and use.
Dan Paterson surveyed items from the Thomas Jefferson Library, a collection that was started with a purchase by the Library of Congress in 1815. Thirty volumes that had been treated since the early 1980s were selected for review. After this initial survey, a second round of 22 volumes from non-Jefferson rare collections were reviewed, also consisting of treatments from the same period. Each book was evaluated and assigned a grade of one through five, with one representing a failed repair and five indicating that no other intervention was needed. Included in the sample were treatments completed using leather, Japanese paper, Tyvek, and linen. 
Treatments in which the book was fully rebound or rebacked in leather appear to be functioning well, with an average rating of 4.2. Common problems observed include discoloration on the pastedowns at the turn-ins, discoloration of the leather along the spine from light damage, and minor cracking along the joints. Some of the treatments included in this set have smaller, supplementary repairs with textured fills the same leather and toned to match, and are still functioning well. Some of the Japanese paper repairs have lifted.
Repairs completed with Japanese paper average a 3.4 on the scale. Treatments in which the Japanese paper is adhered over the leather have a higher rate of failure. The repair material may be lifting the grain layer of the leather and is often tenuously attached. Many of the case studies in this group included additional mechanical board attachment methods, such as board tackets, and were also boxed. The rate of failure could be an acceptable trade-off for the time and cost efficiency of the repair. At the current level of use for many of the books in this group, the Japanese paper repair could remain functional for another 100 years. 
The last group of historic repairs examined used Tyvek and linen across the joint and scored quite high. The method for application of this repair is similar to board slotting, necessitating the lifting of the original spine. The laminated Tyvek and linen are adhered over the joint, as well as to the thickness of the board edge, and under the pastedown. These repairs are less visually integrated than others, due to smooth surface texture and flaking of acrylic from the Tyvek, but are still functioning well.
Successful case studies using Japanese paper as the primary repair material include cased photographs where the hinge was repaired with toned kozo, and an ongoing project in which hundreds of thin bindings have been repaired using board slotting and laser printing title information and color directly on kozo paper. Recent evaluation shows that the repair is holding up well and the project will continue.
The panel concluded by stating that conservators at the Library of Congress use a great deal of leather in their repairs. The conservation program at the library has a long history, and staff tend to work at the institution for many years. This means that new staff are trained in the standard workflows, and treatment approaches has remained very consistent over time. This does not mean, however, that they are not experimenting with new materials. It is necessary to be curious, take risks, and experience failure to push innovation.
Q: For books rebound in new leather, is the staining around the pastedowns caused by acidic degradation or by migration and oxidation of oil?
Paterson: We haven’t done analysis on those volumes to know for sure. But that would be a good question for further research. 
Audience comment: Everyone should be labeling the skins as they receive them from the supplier, including the date of purchase. It can be difficult to keep track as you cut the skin apart, but it’s important for us to document.
Paterson: The staff at Library of Congress label the skins and keep a sample book of all the leathers to help keep track. 
Smith: This is also a good opportunity to make a plug for good documentation practices. We saw a lot of older documentation that did not adhere to good record-keeping practices. For example, a lot of reports just had initials of the conservator on them and did not list suppliers. The more detailed your reports, the more they can inform you later on.
Audience comment: It’s nice to see that the training model at Library of Congress is working out. Another technique that was not mentioned is adhering Japanese paper to Ultrasuede to recreate the bulk of leather. 
Audience comment: It’s interesting that Japanese paper adhered over leather appears to be lifting more than when adhered underneath. We often adhere it over the top to keep the leather from lifting or to make it look nicer. 
Smith: We are also sending leather out to be split so that we don’t have to pare it as much.
David Lanning: To what thickness are you splitting it? Doesn’t that totally take away any strength from the leather?
Paterson: I can’t tell you a number off the top of my head, but since there is additional board attachment underneath, we aren’t relying on the leather as much for strength.
Katherine Kelly, Senior Book Conservator, Library of Congress
Dan Paterson, Senior Book Conservator, Library of Congress
Shelly Smith, Head, Book Conservation Section, Library of Congress
==References==
:BPG Board Reattachment. Book and Paper Group Wiki.
:BPG Animal Skin and Leather. Book and Paper Group Wiki.
:Anderson, Priscilla and Sarah Reidell. 2009. "Adhesive Pre-Coated Repair Materials .The Book and Paper Group Annual 28.
:Barlee, Roger. April 29, 2014. Craft Project BE-S2-3432 - “Development of Archival Quality Leather (PDF).” Report. Accessed June 22, 2018.
:Barlee, Roger. 2017. "Development of Archival Quality Leather (Revisited)." Skin Deep. 43. Accessed January 9, 2019.
:Calcote, Lauren. 2016. “Liquick Leather! No Need for a Professional! … Or Is There?” Poster presented at: Emergency! Preparing for disasters and confronting the unexpected in conservation. Joint 44th Annual Meeting and 42nd Annual Conference of the American Institute for Conservation of Historic and Artistic Works (AIC) and the Canadian Association for Conservation (Association Canadienne pour la Conservation et la Restauration) (CAC-ACCR); 2016 May 11-18; Montreal, Canada. 
:Down, Jane L., Maureen A. MacDonald, Jean Tétreault, and R. Scott Williams. 1996. "Adhesive Testing at the Canadian Conservation Institute: An Evaluation of Selected Poly(Vinyl Acetate) and Acrylic Adhesives." Studies in Conservation 41 (1). 19-44. doi:10.2307/1506550.
:Girard, Ségolène. 2018. "BEVA® 371-based synthetic leather: A Preliminary Investigation on the use of BEVA 371 as a Repair Material for Leather Bindings." Journal of Paper Conservation 19 (1). doi.org:10.1080/18680860.2018.1521018.
:Haun, Werner and Jody Beenk. 2010. "Library Collections Conservation Discussion Group 2010: Conservation in the 21st Century: Revisiting Past Practices and Their Evolution in Institutional Settings. The Book and Paper Group Annual 29.
:Hebert, Henry and Marieka Kaye, moderators. 2018. "Pre-Meeting Symposium: The Current Use of Leather in Book Conservation." The Book and Paper Group Annual 37.
:Knight, Evan. 2016. “Assaying Klucel-G recipes, application methods in the surface consolidation of tanned bookbinding leathers (PDF).” Poster presented at: Emergency! Preparing for disasters and confronting the unexpected in conservation. Joint 44th Annual Meeting and 42nd Annual Conference of the American Institute for Conservation of Historic and Artistic Works (AIC) and the Canadian Association for Conservation (Association Canadienne pour la Conservation et la Restauration) (CAC-ACCR), May 11-18; Montreal, Canada. 
:Kronthal, Lisa, Judith Levinson, Carole Dignard, Esther Chao, and Jane Down. 2003. "Beva 371 and Its Use as an Adhesive for Skin and Leather Repairs: Background and a Review of Treatments." Journal of the American Institute for Conservation 42, no. 2: 341. doi:10.2307/3180075.
:Lanning, David, William McLean, Roger Barlee, Thomas McNeill . 1996-2000. "The Manufacture of Leather, parts 1 - 10". Skin Deep. Various volumes.
::This series of articles in the newsletter of the J. Hewit & Sons company details the leather making process. Parts 1, 2, 3, 4, 5, 6, 7, 8, 9, 10. Accessed January 9, 2019.
:Larsen, René, ed. 1996. "Environment - Leather Project: deterioration and conservation of vegetable tanned leather". In Protection and Conservation of European Cultural Heritage, Research Report 6, 167-187. Copenhagen: The Royal Danish Academy of Fine Arts, School of Conservation.
:Larsen, René, Marie Vest, and Ulla B. Kejser, eds. 1994. "STEP Leather Project: Evaluation of the Correlation between Natural and Artificial Ageing of Vegetable Tanned Leather and Determination of Parameters for Standardization of an Artificial Ageing Method". In Protection and Conservation of European Cultural Heritage, Research Report 1, 165-179 . Copenhagen: The Royal Danish Academy of Fine Arts, School of Conservation.
:Mahony, Caitlin and Ellen Pearlstein. 2014. “Evaluation of Consolidants for the Treatment of Red Rot on Vegetable Tanned Leather (PDF).” Poster presented at: Conscientious conservation – Sustainable choices in collection care. 42nd Annual Meeting of the American Institute for Conservation of Historic and Artistic Works (AIC) ; 2014 May 28-31; San Francisco, CA. 
:Owen, Grace and Sarah Reidell. 2011. “TIP: Cast Composites: A System for Texturing Repair Materials in Book Conservation.” Topics in Photographic Preservation 14 : 250-262.
:Plenderleith, H. J. 1967. The Preservation of Leather Bookbindings. London: British Museum.
:Thurn, Jim. 2018. “Board Slotting and Laser Printed Kozo Treatment Steps (PDF).” Library of Congress Conservation Division Handout.
Category:Materials and TreatmentCategory:Book & PaperCategory:LeatherCategory:Treatment