What are Mordants?

Malcolm Tatum

Mordants are compounds that are used often in the production of various textile products. The main purpose of a mordant is to interact with the fibers of a given material and the dye solution. This interaction helps to ensure that the dye sets properly, without splotching or running. Mordants are employed at several different points in the production process, depending on the type of material used and the desired effect that the manufacturer wishes to achieve.

Iodine can be used as a mordant.
Iodine can be used as a mordant.

There are a number of different mordants that may be employed as part of the process of dyeing and setting the color of a given fabric. If there is a desire to achieve what is referred to as a gram stain, iodine is often used to create the desired result. A number of metallic related compounds qualify for use as mordants, including such salts of aluminum, copper, tin, and chromium. Sodium, potassium and tannic acid are other agents that may be used as mordants.

Silk cocoons. Material made from silk does not respond well to all types of mordants.
Silk cocoons. Material made from silk does not respond well to all types of mordants.

Three basic procedures involving the use of mordants to set dyes are common today. Pre-mordanting is a technique that involves applying the mordant first and then introducing the dye to the material. Meta-mordanting employs the approach of combining the dye and the mordant agent first, then applying the mixture to the material that is to be dyed. The third option, known as post-mordanting involves dyeing the fabric first, then exposing the material to mordants as a final treatment. In all three applications, mordants act as dye setters that will prevent the coloring from running or streaking at a later date.

Some mordants are better suited for use with particular types of fabrics. Cotton is often treated with tannic acid or some type of oil before introducing one of the metallic types of mordants. This process allows the metallic compounds to permeate the cotton fiber with a higher degree of efficiency. Wool typically does not require the use of oil or tannic acid as part of the process, and tends to be very receptive to mordants such as iodine and tin. Silk can be a little more complicated, as it does not respond well to the use of mordants such as potassium. However, chromium agents are generally understood to work very well in the task of setting color in silk material.

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Discussion Comments


Agreed! There are countless resources out there to produce natural, non toxic clothes.

There are a number of natural mordants, including alum (a derivative of aluminum that have been used to purify drinking water for centuries), cream of tarter, and plant derived tannins.
Lets keep in mind that several types of mordants are toxic. It's also important to acknowledge that some synthetic *and* natural dyes can be toxic. This can be problematic when humans come into contact with the dyes in their raw forms, and when they find their way into wastewater.

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