Our Repair Calf is sourced from the Indian sub-continent. The leather is initially tanned at source using mimosa, or materials from the same family of tannins. When the skins arrive in our Edinburgh Tannery, we remove the majority of this original tannage and then re-tan, using Tara or Sumac. In addition to improving the leather with these superior tannages, we also add our Archival tannage, yielding leather that is both durable and a pleasure to use.

You can see examples of our Archival BV Repair Calf on the following finished books: 'Minute Books' and 'Cuts of Craft Workers that are featured in the 'Showcase' area of our web site.

*These skins are produced in a mixture of whole skins or 'sides' (half skins taken from much larger whole skins).

*Average Skin Size: 0.80 - 1.0m² (8½ - 10.75 ft²)
Approx. Cut Size: 80 x 50 cm
Standard Substance: 0.75 mm
Colours available: 8 shades
Grades: II, III and IV

Prices for single skins:
Grade II - £151.00 per skin
Grade III - £132.00 per skin
Grade IV - £85.00 per skin

Quantity discounts will be applied automatically.

This arose because:

• Leather from a specific region could not necessarily be guaranteed to have been made using tannins from that region
• The PIRA test had proved to be unreliable

In addition to this, it was known that the rate of ageing of Bookbinding leathers is increased by urban pollution. The work proved that vegetable tanned leathers re-tanned with aluminium salts had a greatly improved resistance to deterioration, and that chrome/vegetable tanned leathers have greatly reduced durability, especially of the grain. The work resulted in the publication of a British Standard for Archival Bookbinding Leather BS 7451:1991 - Specification for Archival Bookbinding Leather. Unfortunately, although of high archival quality, the leather produced was too stretchy to pare easily and was highly water-resistant. This was partly due to the direction of the research (homing in on the archival properties), and also because of the lack of knowledge at the time regarding semi-aluminium leather production. As a result the general reaction of bookbinders was to try the material once and never come back! This therefore meant that concerned bookbinders and archivists were no better off than they had been before the work was carried out in that they were not in a position to tell a good long-lasting leather (pyrogallol tanned) from a non-lightfast leather (catechol tanned).

The work of Betty Haines was followed by two further European Union funded research projects - the STEP and ENVIRONMENT Leather projects. The result of these projects was an artificial ageing regime, along with recommendations that vegetable tanned bookbinding leathers should be manufactured using pyrogallol tannages, (already done at Hewits) and keeping the sulphate content of the leather as low as possible. The artificial ageing system that was recommended involved heating the leather to 1200C (later 1500C) for 24 hours, and then holding the leather in a polluting atmosphere of 20ppm SO2 and 10ppm NO2 at 400C and 35% Relative Humidity (RH) for 6 days. The process being carried out 4 times in total.

Craft Project BE-S2-3432 – “Development of Archival Quality Leather” was a pan-European project intending to have a fresh look at the whole archival leather position. The group was made up of tanners, bookbinders and research bodies from the UK, Germany, Italy and Greece, and the major objectives at the start were as follows:

1. Evaluation of leathers currently used for bookbinding across Europe.
   
2. To develop a leather quality testing scheme, that defined binders requirements in an objective manner understood by both the tanner and the binder.
   
3. Optimisation of semi-metal tannage, whereby a leather with all the required properties could be produced with a life expectance of twice the normal life of the vegetable tanned leather stored in polluted atmospheres.
   
4. To investigate the applicability of innovative “metal-free” tannery processes to consistently produce archival quality tannages.
   

During the first year of the project 72 modern bookbinding leathers representing the whole spectrum of European bookbinding and archival quality leather production were studied. The leathers were tested for their physical and chemical properties, and in addition the bookbinders graded the leathers on their feel and handle as well as on how easily they pared and could be used for binding. These organoleptic tests (as they became called) graded the leathers from 0 (completely unsuitable) to 4 (ideal), with an overall result of 3 (or 4) needed for a pass not surprisingly it was ONLY the leathers produced by specialist bookbinding tanners like J. Hewit & Sons Ltd that passed!

As one can imagine, this resulted in a mass of data from which it became apparent that there was correlation between some of the physical tests carried out on the leathers and the organoleptic tests. However the best correlation invariably resulted from new objective tests specifically aimed at mimicking the handling and working of the leather by the bookbinder. During the second year the physical tests were narrowed down to the following:

Softness - a measure of how soft and elastic the leather felt

Wettability - new test indicating the absorbency of the leather to paste and glaire

Mouldability - new test correlating to how easily the leather may be moulded and retain its shape during bookbinding

Notch Sensitivity Factor - new test to assess how easily a leather could be pared or shaved during bookbinding

In addition to the above, the Resistance to Flexing whilst under strain was measured as an indication to the strength of the leather on the joint. Together these tests resulted in a specification for a craft bookbinding leather (Appendix B). The methods for the 3 new tests can be found in Appendices D-F.

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