Editing Tanning (leather) (section)

=== Vegetable tanning ===
Vegetable tanning uses [[tannin]]s (a class of polyphenol astringent chemicals), which occur naturally in the bark and leaves of many plants. Tannins bind to the collagen proteins in the hide and coat them, causing them to become less water-soluble and more resistant to bacterial attack. The process also causes the hide to become more flexible. The primary barks processed in [[bark mill]]s and used in modern times are [[chestnut]], [[oak bark|oak]], [[redoul]], [[tanoak]], [[tsuga|hemlock]], [[Quebracho tree|quebracho]], [[mangrove]], [[acacia|wattle]] (acacia; see [[catechol]]), and [[myrobalan]]s from ''Terminalia'' spp., such as ''[[Terminalia chebula]]''. In [[Ethiopia]], the combined vegetable oils of Niger seed ([[Guizotia abyssinica]]) and [[flaxseeds]] were used in treating the flesh side of the leather, as a means of [[Tanning (leather)#Tawing|tawing]], rather than of tanning. In [[Yemen]] and [[Egypt]], hides were tanned by soaking them in a bath containing the crushed leaves and bark of the Salam acacia (Acacia etbaica; A. nilotica kraussiana).<ref>{{Citation |contribution=Hil. Tefillin, u'Mezuzzah weSefer Torah |title=[[Mishne Torah]] |last=Qafih |first=Y. |author-link=Yosef Qafih |volume=2 |publisher=Mekhon mishnat ha-Rambam|place=Kiryat-Ono|year=1985 |page=312 (note 17) |language=he |oclc=19158717 }}</ref> Hides that have been stretched on frames are immersed for several weeks in vats of increasing concentrations of tannin. Vegetable-tanned hide is not very flexible. It is used for luggage, furniture, footwear, belts, and other clothing accessories.