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TWO-STEP MORDANTING: TANNIN and AL acetate

Two-step mordanting: tannin and aluminum salt.

Cellulose fibers possess inherent properties that enable them to form bonds with tannins, though these initial bindings are relatively weak on their own. However, when aluminum is introduced into the mix, the situation dramatically changes. The aluminum acts as a mordant, significantly enhancing the strength and durability of the bond between the tannin and the cellulose fibers. This interaction not only stabilizes the tannin within the fiber structure but also prepares the fibers for more vibrant and long-lasting dye absorption. As a result, the combined action of tannin and aluminum creates a robust mordanting effect, crucial for achieving rich, deeply saturated colors that adhere effectively to cellulose textiles.

The lengthy sequence includes the following steps:

  1. Washing the item to be dyed in a washing machine using washing soda (sodium carbonate), followed by a thorough rinse.

  2. Tanning.

  3. Drying.

  4. Mordanting.

  5. Drying.

  6. Washing out in soapy water without scrubbing.

  7. Rinsing.

  8. Dyeing.

The Tanning Process:

  • The item to be dyed, already washed and dried, is weighed.

  • 10% of oak gall extract, relative to the weight of the fiber to be galled, is weighed out.

  • The tannin is dissolved in lukewarm water.

  • The fabric is then immersed in the clear solution.

  • The temperature is raised and maintained at 70°C for one hour with stirring. If possible, the fabric is left to cool overnight in the bath, ensuring it does not float.

  • The fabric is rinsed and dried. It is now ready for mordanting but can be stored for some time without any issues before being mordanted with aluminum acetate. The fabric will be cream-colored and even, which can be easily verified by simple visual inspection. Note: If it is uneven at this stage, achieving an even dye result later will be difficult.

Advantages of This Treatment: Using this treatment, the colors derived from flavonoid-type dyes are more saturated and more solid than those obtained from mordanting alone.

The Mordanting Process:

·         Prepare aluminum acetate solution as follows: In 300ml of white vinegar, dissolve 15g of alumina sulfate and 7.5g of sodium carbonate. Once the effervescence has ceased, ensure that the ingredients are fully dissolved and the solution is clear before soaking the fabric.

  • Soak the fabric in this solution with stirring, wring and dry

  • Wash  in soapy water without scrubbing, rinse well.

  • Fabric is ready for dyeing.

 

Results from Michel’s experiments:

In all baths, the "tannin/acetate" formula yields the most saturated tones, followed by the "acetate" formula, and finally, the "tannin/aluminum sulfate or alum" formula gives the lightest results. If one prefers the pale tones produced by this formula, it is sufficient to choose the best mordant and reduce the doses of dyes,  

Conclusions of this trial are: a. The acetate mordant is more effective; b. Galling improves results but is less decisive than the choice of mordant since the "tannin/sulfate" sequence yields the poorest results.



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