My son is doing a science fair project on the difference of synthetic and natural dyes. can you give him any information on his topic? 

The biggest issue is matching the right dye to the right fiber. Many dyes work much better on wool than on cotton, and almost none of them do very well on synthetic fibers, except for nylon which dyes a lot like wool, and rayon which is much like cotton. It would be ridiculous to test your synthetic dye by using a cotton dye recipe on wool, or a wool dye on cotton, unless that is the point of your research study; using a dye intended for the wrong fiber will yield very poor rtesults. The best synthetic dyes for cottons are the fiber reactive dyes, while the best synthetic dyes for wool include the acid dyes, such as food coloring. The question your son asks should be specific about which fiber he is using, e.g. "A Comparison of Dyeing with Beet Juice and Kool Aid on Worsted Wool".

Most randomly chosen natural substances are poor dyes. If your son compares beets or berries or flowers to synthetic dyes, the synthetic dyes will come out ahead every time. However, some natural dyes are excellent. Most of these are not readily available, but must be purchased by mail order (e.g., cochineal, cutch, fustic, indigo); purchasing natural dyes always costs far more than purchasing an amount of synthetic dye that will color the same amount of fiber. My son mail-ordered some dye and mordants from Aurora Silk for his science fair project, and received them in less than a week; they seem to be a very nice company to deal with. If you don't have time for that, you will have to stick to readily-available natural dyestuffs, such as turmeric or walnut shells. Beets are a fine example of a very poor dye. This is always surprising, because the water in which beets have been cooked looks so deep and rich and dark red that it seems as though it must be a good dye. The only fiber that we found to pick up much color from being boiled in beet water was wool, and that turned a light yellowish brown, not red. Even expensive cochineal performed poorly on cotton with or without an alum mordant, though it worked wonderfully on wool, silk, and nylon. Turmeric was the only natural dye we tested that worked at all well on synthetic fibers such as polyester and acrylic, though my books on natural dyes assure me that it is not very lightfast and tends to fade; it can be expected to fade long before a good synthetic dye would do.

In using natural dyes, it is important to use plenty of dyestuff. My son used a pound of beets to lightly dye two small swatches of fabric. In most cases, you should use an equal weight of dyestuff to fabric, or even twice as much. There are exceptions, however. Cochineal and turmeric require only a small spoonful of dye for a piece of fabric, similar to synthetic dyes. 

Most natural dyes require a mordant; popular synthetic dyes do not. The safest mordant is alum (aluminum potassium sulfate); you can sometimes find it at a nearby pharmacy, but if not you can purchase it from a dye supply company. You can apply it by boiling the fabric in the alum water, then rinsing it in cool water, and finally boiling the fabric in the dyebath. Most dyes, including natural dyes, require boiling the fabric in the dyebath; only fiber reactive dyes work well in room temperature water. Artificial food coloring is a good dye for wool, if you boil the wool in it, but it does very poorly on cotton. A nice science fair project would be to compare the performance of Kool Aid as a dye on cotton to its performance on wool. The food coloring, since it is an acid dye, will mostly wash out of the cotton, but will dye the wool nicely.

Your son will need to get books to use as references. A good book on natural dyeing is invaluable for learning how to apply natural dyes. Check the public library for any books on the subject of dyes and dyeing. See if books can be ordered from another branch of your library system. Look in particular for "Synthetic Dyes for Natural Fibers", by Linda Knutson, if possible. Your son may also use my website as one of his references. Note that the creation date for each page on my site is given at the bottom.

Finally, there is the question of quantifying your data. My son's school requires that the test results be digitized and graphed. How are you going to turn your dye results to numbers? What my son did was scan the swatches onto the computer, then use Adobe Photoshop Elements, under 'Histogram', to determine the luminosity on a scale of 1 to 255. He converted this value to a value for intensity by subtracting it from 256, and was able to prepare graphs of his results this way, for a project comparing the performance of Procion MX dye on cotton at various pH levels.  I am not sure how reliable this method is for scientific purposes, but the numbers corresponded very well to our visual observations.

Please see the following for more information:
About Dyes
About Natural Dyes
Books and Videos on Hand Dyeing
Sources for Dyeing Supplies
Natural Dyes Are Not Superior to Commercial Dyes (science fair question)
Aren't natural dyes safer than synthetic dyes?
Is there a natural way to set natural dyes?
A Science Fair Project Regarding Dyeing Using Different Waters
How can I set the dye from pounding flowers onto cloth?


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