Our Sulfur Free 100% Vegetable Tanned and Sustainable, or SF Calf leather, is being manufactured using a very specific and researched tanning and re-tanning process in which mineral tannins (eg. chrome and/or aluminium) and sulphited, sulphated or sulphonated components (eg. fatliquors; synthetic tannins; classic unhairing chemicals) are completely avoided. The leather is lab tested to be Sulfur Free. The main tannage is done with pyrogallic tannins. This calf has no grain manipulation and follows the recommendations of mid.20th century literature so that it is theoretical Archival. Due to this it should last longer than any other vegetable tanned leather which has been produced with sulfur-containing compounds used in any form. We are the first in the market place to manufacture this technically challenging leather. This is currently in testing. For more information on current test results for this product and the comparison test leathers, please contact us at [email protected]
From the literature we know when “modern” tanning started to be used around 1830, leather produced for bookbinding had a dramatically reduced lifespan in comparison to SOME earlier produced leather which had a lifetime measured in one century or more. Our SF Calf leather duplicates the leather chemistry prior to that era to the best of our literature searches and consultations with other leather chemists/conservators. Most substances used are naturally occurring. All are sulfur-free, avoiding potential oxidation to degradation products.
The organoleptic properties are excellent as informed by some of our customers who have worked with the material. It tools, covers, pares at least similar or better than any calf currently or previously produced in the modern era. We have had several initial comments saying that this will be their “go to” calf for all future work.
Lubricating the leather is done by using raw, filtered, oxidized fish oil in combination with Marseille soap and raw lecithin and other natural products. This procedure avoids usage of ANY sulphited or sulphated/sulphonated oil. The “mix” is created in such a way that it emulsifies well with the tannins and penetrates even into the leather and, at the same time, keeping the grain well oiled to avoid grain crack. The same oil combination is applied during retannage as well.
In the main tannage we use mainly a chestnut liquid (hydrolysable) and Sumac (hydrolyzable) and a sustainable natural product – since human memory available – made from agricultural waste. The last one is rich in sugars and salts which all help with long-term durability. In retannage we use only a liquid Gambier extract (catechins and catechu tannic acid) and organic fillers.
There are no vein marks. The leather is naturally (hang) dried. The properties of the leather come from the tannage and retannage.
This leather is exceedingly expensive to manufacture. It is priced at $19/ft, but please compare this to $30/ft for other calfskins which do not work with the same ease.
Flex Test Results (IUP-20) as of 26 August 2020. Requirements for “archival” vegetable-tanned bookbinding leather are minimal 2,500 flexes. Per the video, this leather stands up to 100,000 or more flexes wet and dry. This is very high, indeed, for purely vegetable-tanned leather.
100, 000 flexes and still going strong.. Very promising