Potassium aluminum sulfate is the mordant most frequently used by dyers for animal and cellulose fibers and fabrics. It improves light and washfastness of all natural dyes and keeps colours clear. It is inexpensive and safe to use (but should not be ingested). This form of alum is refined from bauxite, the raw state of aluminum ore, and is free from the impurities some other alums can contain (such as iron). Use at 12-20% wof.
Natural dyeing – mordanting any fibers : potassium aluminum is the easiest and most popular mordant used with natural colours. It does not change the shades and is necessary for a good fixation of the natural colours.
For protein fibers (wool or silk), we recommend to use the alum associated with cream of tartar that improves the fixation of alum to the fiber.
For cellulosic fibers (cotton, linen, hemp, abaca…), we recommend to use alum in association with sodium carbonate. If you prefer to use a single product, you can also select aluminum acetate instead of alum.
Also, combinations of aluminum and iron mordants or a last (very light) iron bath after a aluminum-mordanted-colour will widely increase the number of shades.
Natural inks : potassium alum both contributes to stabilize the natural dyes molecules (by complexation) and to better develop their colour. Our plant dye extracts can be used for the preparation of natural inks, for instance in combination with arabic gum. Alum has also bacteriostatic properties on certain bacteria and plays a role on the preservation of products.