Name: Mindy
Message: I was wondering if you could help me with some research on my science fair. I am making dyes from fruits to dye cotton. I was wondering what would be the best way (and easiest) to dye the cotton, and if you have any information on natural fruit dyes. Thank you!

The most important thing to know about natural dyes is that, as a rule, they will not stick to cotton permanently unless you mordant the cotton first. Sometimes you may see household products such as vinegar or salt referred to as mordants, but they are not true mordants at all, and will not enable the dye to persist on the fabric. You must use a proper mordant if you want your dye to stick to the cotton. If the coloring agent does not stick to the cotton when it is laundered, it is not truly a dye at all, merely a stain.

You do the mordanting as a separate step before dyeing. Good mordants for use on cotton include alum, chromium iron, and copper. Alum is by far the safest of this group, though it can be toxic if ingested. I recommend that you consult Jill Goodwin's second edition of A Dyer's Manual (2003), which gives the following recipe for mordanting cotton. First soak the cotton in water for at least an hour. To mordant 8 ounces of cotton, dissolve 2 ounces (60 grams) of alum and half an ounce (4 teaspoons or 20 ml) of washing soda in a pot of boiling water, then boil the cotton in the alum water for half an hour, stirring occasionally. Leave the cotton to cool in the liquid, then, when it is cool, gently squeeze the extra liquid from the cotton.

To dye the mordanted cotton, use twice as much dyeing material, by weight, as you have cotton to dye (weigh your cotton before you start). Soak the fruit in water for one to two days, then boil it in this same water for an hour, then strain out the solids and keep the liquid for use as a dyebath. Boil the cotton in this liquid for an hour and let it cool in the dyeing liquid. Using an acid such as vinegar or cream of tartar in the dyebath will often improve the color of fruit dyes.