A mordant or dye fixative is a substance used to set (i.e. bind) dyes on fabrics by forming a coordination complex with the dye, which then attaches to the fabric (or tissue). It may be used for dyeing fabrics or for intensifying stains in cell or tissue preparations.

Do you have to use mordant?

Mordanting is the most important process of preparing fibers to accept color. This is not an optional step but there are many mordant variations, and indigo as a vat dye does not require a mordant. Using a mordant helps to ensure the most durable and long-lasting colors.

Do you need mordant for natural dye?

To achieve bright colours with natural dyes, you need to mordant your wool, cotton or silk beforehand. With the exception of woad and indigo, most natural dyes do not adhere very well to the fibres and need the help of a mordant. A mordant is a chemical binding agent that adheres well to both the fibres and to the dye.