BPO: Tannins

Beschrijving van de dienst

What are tannins Tannins are a group of bitter and astringent biomolecules that appear in the plant world. They can be found in barks, wood, galls, leaves and fruits of different plants. The term tannin comes from the Anglo Norman word tanner, which refers to oak bark. Tannins make the plant material unpalatable for insects, and make it harder for fungi and other harmful pests to enter the plant or tree. These anti-microbial, -viral and -fungal qualities make is nature's self regulating antibiotics. ​Tannins have been historically used for medicine (because of its' astringent properties), for tanning leather and for natural dyeing. ​In food, tannins are present in cacao, coffee, wines and tea, creating an astringent and bitter taste. We can divide tannins in three different classes: 1 - Gallic tannins. (hydrolyzable tannins) Clear tannins that do not add much colour to the fabric such as . tara, . oak galls, . oak bark . oak nuts . sumac (leaves and galls). . blackberry leaf 2 - Ellagic tannins. (Gallic tannins in combination with Ellagic acid) Tannins with a lot of Ellagic acid, sometimes in combination with flavonoids that will add a yellow colour to the fabric such as . myrobalan, . pomegranate . henna . walnut hulls . pecan hulls . chestnut bark. 3 - Catechic tannins. Condensed tannins that will add brown and reddish hues to the fabric such as . black tea, . cutch, . quebracho . Acacia mearnsis extract (mimosa tannin) . persimmon . ceriops tagal Tannin affinity Tannins love proteins so they bind easily with silk and wool. They also love amino-acids and alkaloids which makes them a great pairing for cotton. Heating brings out the colour more, if the material has any. Example: pomegranate rind soaked cold will give a soft buttery shade, but if I heat it it will become a vibrant yellow. Of course you can play around with these variables. In percentages of WOF it is important to know the % of tannin in your raw materials. Oak gall tannin from the shop has around 70% gallotannins, sumac leaves have around 30%. That means that you may have to adjust recipes if you are swapping the raw materials. Reaction of tannins with ferrous sulfate Tannins react to mineral salts, the most known and obvious being ferrous tannin. Tannin in combination with ferrous sulfate form a strong insoluble bond called ferrous-tannate. They are shades of grays and black depending on the percentages. Different tannins may give different shades: the gallotannins have