What are Gallnuts and Gallnut Extract?
- What colours does Gallnut extract produce?
- Why is tannin important?
- How do I use Gallnut extract as a mordant?
Gallnut Extract (a natural substitute for tannic acid)
1) What are Gallnuts and Gallnut Extract?
Plant galls are abnormal outgrowths of plant tissues caused by various parasites, particularly insects. Oak marble galls and Chinese sumac galls are galls on oak and Chinese sumac, respectively, which resemble nuts and are called "gallnuts" or "nutgalls". Oak marble galls, found on oaks in the Middle East, have long been used to make high-quality ink and for dyeing but most gallnut extract is now from Chinese sumac trees. It is now difficult to find oak galls, which were previously collected by hand in Turkey. However, the gallnut extract from Chinese sumac is very similar to oak gallnut and has the advantage of having a slightly higher concentration of tannin.
The gallnuts that appear on leaves of Chinese Sumac (Rhus chinensis) are the result of the activities of an aphid and the galls are 3 to 6 cm long and irregular in shape according to Cardon. They are very rich in tannin.
2. What colours does Gallnut extract produce?
When used on its own gallnut extract produces beiges on wool, cotton and silk. With an iron after-bath, the colour changes to greys and black. This extract can also be used to sadden other colours.
However, gallnut extract is also very useful for the mordanting effect of the tannin.
3. Why is tannin important?
Mordants like alum do not attach very well to cotton and other plant fibres. This is where tannins are very useful as they attach easily to plant fibres. This process is called ‘galling’. The fibre that has been treated with tannin can then be mordanted with alum, the tannin forming an insoluble compound with the alum and natural dyes resulting in fast colours. Tannins are also used for turning animal skins into leather.
4. How do I use gallnut extract as a mordant?
You can use gallnut extract instead of tannic acid when mordanting cotton and linen, as it costs less than using tannic acid. Use the same amount as tannic acid, about 6 grams per 100 gram of fibre. Check out mordanting with alum and tannin.
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