Name: Manini

Message: I have this design lab that I have to plan for grade 12 chemistry. The only thing my teacher indicated was it has to be about the factors of the dying process. She said the only thing we cannot do is concentration and time. I was wondering what can I do which makes one dependent variable, one independent variable and rest of them as controls? Thank you for reading through my message. 

I like chemical variables, such as pH.

First choose a good dye. Don't use a dye that you don't know what chemical it is, such as Rit or Tintexdye, whose dye ingredients are all secret. Use a fiber reactive dye, or an acid dye. (Fiber reactive dyes are good for cotton, and acid dyes are good for wool and nylon.) 

If you go to a good crafts store (not the grocery store!), you should be able to find fiber reactive dyes in the form of a good tie-dye kit. Avoid the tie dye kits made by Rit and by Magic Strings; look for a tie-dye kit containing the colors turquoise, magenta, and yellow. I can tell you what chemicals the dyes are. Don't get a kit with true red and royal blue, because the dyes in these colors are premixed colors, not chemically distinct. Although Dylon dyes include some good fiber reactive dyes, they are in most cases mixtures, so not suitable for an experiment. If you're very lucky, your crafts store might carry Jacquard Procion MX dyes, so you can choose unmixed colors among them. (They don't say which are unmixed on the label, but I can tell you which are good.) Or, if you have time to mail-order (it only takes a week or so for delivery), you can order from a company such as Dharma Trading Company or PRO Chemical & Dye. You can mail them a check if you don't want to use a credit card.

If you choose a fiber reactive dye, you could vary the pH of your dye reaction, or you could vary your fabric (see how much better cotton dyes than polyester), or you could vary the dyeing temperature (fiber reactive dyes require warm temperatures and will not work in ice water).

You can use an acid dye instead of a fiber reactive dye, for your experiment. There are lots of different kinds of acid dyes, and I recommend, as with fiber reactive dyes, that you choose a known dye, with a known chemical structure. Food colorings work well for this; they are not the best textile dyes, but they can work on wool, and you can find pure unmixed food colorings. Again, as with fiber reactive dyes, varying pH will have dramatic effects, though in the opposite direction. While fiber reactive dyes require a high pH on cotton, acid dyes require that you add an acid, such as vinegar, to your dyebath. They also work best with some boiling, so another option would be to vary temperature: room temperature versus hot water versus a boiling water bath as your independent variable. Use acid dyes on wool, silk, or nylon, never on cotton (unless you independent variable is fiber content and you are comparing cotton to one or more of the fibers that acid dyes actually work on). 

Alternatively, the most convenient natural dye to use in your experiment would be turmeric, since it is a spice that is readily available at the grocery store. It's not a great dye because it fades in the light and must be redyed fairly often, but it's very easy to use. It works better with an alum mordant than without one, but it does work without a mordant. If you get some alum mordant (which I can explain to you), you could compare how well turmeric works as a dye with and without mordanting the fabric first.

In every case, your dependent variable will be density of color on the fabric (or yarn) after you dye it and then wash out the unattached dye. Get some pH paper and dye with your selected fiber reactive or acid dye at a pH of 2, 4, 6, 8, 10, and 12. You can make nice graphs with the numbers you obtain for the color intensity of your dyed fabric.

I strongly advise you to read through the entries on my "All About Hand Dyeing Q&A" blog under the topic "schoolwork" for ideas, and also to find the article explaining how to turn your different intensities of color into numbers that you can make graphs of.

Also check my FAQ, for questions such as "What is the effect of pH? What is the optimal pH?", or "What kinds of chemical bonds hold dyes to fibers?", or "What is the chemical structure of Procion type dye?".

Thank you for taking the time to read my message and emailing me. I like the idea of density of colour vs. pH. I have read through your other Q&A pages and I think I can measure the density of the colour through the process you described for Photoshop elements. My question for pH is how would I vary it? To maximize the amount of controls, I would need everything to be constant except the amount of hydrogen ion concentration (e.g. pH). Do you have any idea how to go about this procedure?

Yes, that's the easy part.

For an acid pH, use distilled white vinegar (which is 5% acetic acid). For a moderately acid pH, use a dilute solution of white vinegar in water. You can also buy citric acid in the canning department of the grocery store or at a wine brewing supply store. Dyeing supply stores sell additional chemicals for this purpose, but vinegar or citric acid should be sufficient for your needs.

For a mildly basic pH around 8, use sodium bicarbonate (baking soda), about one teaspoon per cup (5 ml per 250 ml). For a more basic pH round 9, mix sodium bicarbonate with sodium carbonate (soda ash). For a pH around 10.5 to 11.5, use sodium carbonate in water, about one teaspoon per cup (5 ml per 250 ml). Sodium carbonate is sold in the hardware store among the swimming pool supplies, as a pH increaser. Be careful that they do not sell you bicarbonate when you want carbonate. You can also use washing soda, if it is free of dyes and perfumes. This is often sold in the grocery store. (See "What is soda ash, and what's it for in dyeing?".) For a pH of 12, use trisodium phosphate, sold in the hardware store as a cleaner to use on outside walls before painting. You would use sodium hydroxide or hydrochloric acid in the lab, but these household chemicals are easier to work with safely.

You will need to get pH paper. I like the pH paper at Ward's Natural Science, but first check and see if your science teacher can supply you with pH paper. Mix your pH solutions, without adding the dye, and then check their pH carefully with the paper. Obviously, you cannot use pH paper to test the pH after adding dye, but testing your solutions without dye works fine.

You can buy quart canning jars from the grocery store or some hardware stores to do your dyeing in. They work very well. If you are using a hot water dye such as any acid dye, you can place several canning jars inside a cooking pot with about two inches of water in the pot, without contaminating it. Do not use your dye chemicals directly in household food preparation containers, unless you are using only certified food coloring as a dye.

Be sure to use a 100% natural-fiber fabric without any permanent press or stain-resistant finishes. Prewash your fabric in HOT water with detergent and extra soda ash (washing soda) to help remove interfering factors that will prevent even dyeing. Use cotton, linen, or hemp fabric for fiber reactive dyes; use wool fabric for acid dyes. (Nylon and silk can also be dyed with acid dyes, but not as well.)

If you have additional specific questions I will probably be able to help you with them.

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