The Role of Tannin in Eco printing

What are tannins?

Tannins are a type of organic compound that are found in various plants, particularly in tree bark, leaves, fruits, and seeds. They are known for their astringent properties. This astringency can cause an unpleasant sensation in the mouth. This is due to their ability to bind to and precipitate proteins in the saliva and oral mucosa.  It’s the way that plants have to defend themselves from being eaten by animals.

They have many practical applications. They are commonly used in the production of leather, where they help to stabilize and strengthen the hides. They are also used in the production of wine and beer, where they contribute to the flavor, color, and stability of the final product. In addition, tannins are used in traditional medicine for their anti-inflammatory and astringent properties. They also have antioxidant and anti-inflammatory properties, and may help to improve digestion and reduce the risk of certain types of cancer.

Potential drawbacks: While tannins can have many positive effects, they can also have some negative effects. Excessive consumption of tannins can lead to gastrointestinal discomfort, and can interfere with the absorption of certain nutrients, such as iron. That’s why some people think that drinking tea after meals is not beneficial: the tannin in the tea will “absorb or sweep” all the iron in the food we have just consumed.

Tannins in the mordanting stage

This same astringent  character makes tannins useful for fixing colors to fabrics. This can be more specifically applied to the natural dyes field, but anyway it’s worth mentioning here.

Let’s  understand then why we can use tannins as mordants:

  • Tannins have the ability to form chemical complexes or bonds with both the dye molecules and the fabric or fiber. They can create a bridge between the dye and the material, improving the adhesion of the dye to the fibers.
  • Dye fixation: Tannins can help fix the dye to the fabric or fiber by forming insoluble complexes with the dye molecules. This enhances the colorfastness of the dye, making it more resistant to fading during washing or exposure to light.
  • pH stabilization: Tannins have a natural acidic nature, which can help stabilize the pH level during the dyeing process. Maintaining the appropriate pH is crucial for achieving desired dye colors and preventing color variations.
  • Increased color intensity: Tannins can also enhance the color intensity of some natural dyes. They can react with the dye molecules, leading to deeper and more vibrant shades.
  • Compatibility with natural dyes: Tannins generally work well with many natural dyes, especially plant-based dyes. They can interact positively with a wide range of dye sources, including plant materials, barks, leaves, and roots.
  • Environmental friendliness: Tannins are  natural elements, which makes them a more eco-friendly option compared to some synthetic mordants. They are biodegradable and have a minimal environmental impact.

Tannins in the ecoprint process

In the field of ecoprint , tannins are multifunction stars.  

With them, we can create prints with a process which is environmentally friendly because it doesn’t use any harsh chemicals or synthetic elements. Instead, the simple natural reaction that tannins produce in the presence of iron,  creates beautiful, unique and sustainable textile designs.

 Let’s see how we can use tannins:

First of all,  they can help us get wonderful leaf prints and contours.

Yes! When tannins in the plants and iron in the fabrics come together, magic happens. The interaction of tannin and iron is perhaps one of the foundation stones of the ecoprint “science”

We can surely say that tannins play a significant role in the eco printing process. When they are combined with iron (either in the fabric or in the blanket) , a chemical reaction occurs, which can create a permanent and natural print on fabric. “Permanent” is a good concept for us eco printers: this print produced by the tannin and iron reaction is very likely to have a pretty good light and wash fastness. Certainly music to our ears.

If a beginner eco printer asked me….”Which plants are good to start?” The answer could be “those which contain a lot of tannin”: castor oil, liquidambar, casuarina, oaks, walnut, tamarix, sumac, acalypha, grevillea, eucalyptus …………Because, following the due process, for sure the outcoming prints will be very satisfactory. And also because to get a good print from them you will only need iron and not more complicated mordants.

Look how beautiful can be the prints you achieve just bringing together tannin rich plants and iron: even within the boundaries of the grey or black shades it’s possible to get an appealing  “Chinese ink style” in your prints

Something important: bear in mind that the print that we can get from bringing together the tannin in the leaf and the iron in the fabric or blanket, it will always be grey or black.  Even when some tannins contain colors, as we will see now. 

Tannins can also be used  to create colorful backgrounds

In the previous paragraph we saw how to make the most of the tannins present in the leaf veins or contours.  But we can also extract tannins from other parts of the plant like fruits, barks or the wood itself. In this case, we might be able to get colors (or dyes) as well.  Regarding colors, we can divide the tannins like this:

Gallic tannins (colorless tannins) they mostly produce a grayish/purplish color when met with iron: oak galls, tara, sumac…………….

Ellangic tannins (yellow shades)….myrobalan, pomegranate, green tea, acacia, ….

Catechic tannins (reddish/brownish) quebracho, clutch, Black tea, chestnut bark, walnut husk, eucalyptus bark, …………….

If we learn how to handle tannin colors, we will be able to achieve an amazing palette of backgrounds that will perfectly match the sophisticated look of botanical prints.

In my eco printing course The Full Palette, I develop this idea along several chapters.  Combining tannins in the blankets with the different concentration of mordants in the fabrics you will be able to add colorful backgrounds to your prints.

See how the tannin colors look on the 3 different concentration of mordants:

 And it´s not only a matter of color and your aesthetic approach: by adding a background to your prints you can put any plants in your bundle because, regardless of their ability to print or not, you will be creating a background around the leaf and the result will be astonishing. Of course you can use other dyes to create a background , but personally I think tannin colors in the background are the perfect match for my prints.


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