Narration : 8. Natural Dye and Mordant
- In chelate titration, you observe the color changes in which the indicator coordinates with the metal ion.
- Also, you confirm the presence of aluminum ion by aluminon lake which is derived from aluminon adsorption to aluminum hydroxide.
- The related reactions between organic dyes and metal ions play a vital role in the usage of mordant in the process of natural dyeing.
- By dyeing cotton cloth with organic dyes extracted from onion skin and metallic mordants, let us observe the working of metal ions.
- First, add water to onion skin and heat for 20 minutes.
- After heating, filter the mixture to obtain dye solution.
- Soak the cloth in the warm dye solution for 10 minutes.
- Remove the cloth and wring lightly and soak it in mordant containing metal ions for 3 minutes to fix the color.
- The pigment binds to the metal ion to color brilliantly. Further it becomes water resistant and the color does not run easily.
- Here, the common alum that is aluminum potassium sulfate is used as a mordant.
- To understand the effect of the mordant, let’s compare the color and solubility of dyes where mordant was used and one where it was not.
- Wash well with water both the samples one that was soaked in the mordant and one that was not.
- The sample not soaked in the mordant does not color well. On the other hand, the one soaked colors perfectly.
- Finally dry the cloth.
- If iron or copper mordants are used instead of aluminum mordants, even though the same pigment is used one can get different colors.
- Moreover, the coloring of the solution differs according to metal.
- These facts also prove that the organic pigments coordinate with the metal ions.