Name: elliot
Message: hi, I'm a high school student and I am doing a science fair project on dyeing. I'm testing whether pH has an effect on the color shade. I'm going to be dyeing cotton fabric. The one problem with the experiment is that I don't know exactly how to measure the shade, I was planning on just getting the paint color samples and matching them to those shades. I was wondering if you had any sugestions or if you thought that was the best way. 

What kind of dye are you going to be using? It is very important that you be able to specify exactly what dye you use, in your project. If you buy the right kind of dye, you can give the scientific name and even the chemical structure of the dye. However, if you buy Rit brand all-purpose dye, you will not be able to say anything at all about the specific dye you are using, because they keep it a secret from their customers. I strongly recommend against using all-purpose dye in science projects.

If you use a fiber reactive dye, you will know a lot more about your dye, and your project will be much more scientific. Often local crafts stores will carry Tulip brand tie-dye kits, which contain an excellent form of fiber reactive dye called Procion MX dye. Some fabrics stores also carry Dylon Permanent brand dye; the dye ingredients for many of the Dylon Permanent dye colors are listed here: "Dylon dyes", posted 9/27/2006. If you have time, you can mail-order good Procion MX dyes through Amazon (see colors and names for ordering Procion MX dyes through Amazon) or from any of the various dye suppliers list on my chart of Sources for Dyeing Supplies Around the World.

Cotton is a good choice; be careful to use cotton that does not have any suface finishes, such as stain-resistance or permanent press, and prewash it in hot water before you use it. It's important to  make a clear description in your project results of exactly what fiber type you are dyeing. For most dyes, the best fabrics to use are 100% natural fibers, such as cotton or wool. (Superwash® treatment of wool is okay.) Some dyes work well on one fiber, others on a different fiber: see "About Dyes" on my website. It can make for a better project to compare the effectiveness of one dye on two very different fibers, such as cotton (which is cellulose) and wool (which is a protein). You will see that wool takes dye well at an acid pH, while cotton takes dye only at a basic (alkaline) pH.
 
When my son did a science fair project in middle school comparing the effects of pH on a specific dichlorotriazine dye, he used Procion Red MX-5B (also known as Color Index Reactive Red 2: see the different names on my chart of "Which Procion MX colors are pure, and which mixtures?"). He compared the action of this dye at a specific room temperature (don't forget to write down your own room temperature, and be sure your room is at least 70°F or 21°C or above for your dye reactions), at various pHs. He tested his dyebath pHs with pH paper before adding the same amounts of the same dye concentrates to each one. 

I helped him with the measurement step after he had washed the fabric samples in cool and then hot water (I recommend a net lingerie bag for easily washing all of the samples at once in the washing machine) and allowed them to dry. Since you are in high school, you will probably be able to manage it by yourself. He used an ordinary digital computer scanner to scan in all of his different samples as one image, arranged on the scanner at one time. It is important to scan them together, because one scan may have a different overall color cast or brightness than another; scanning them in one pass helps to maintain consistency. We used Adobe Photoshop Elements 2.0. On the version of the program I have available now, Adobe Photoshop Elements 3.0 for Mac, the function we used is under the "Window" menu; click on "Histogram" to see a graph of the color intensity. We selected the channel labeled "Luminosity", and, after selecting a representation section of a color swatch with the Rectangular Marquée tool, wrote down what appeared as the mean value, as well as noting down the standard deviation. Now, the luminosity has a maximum value of 256. What my son was interested in was not the luminosity, but rather the intensity of dye color. To get the value for dye intesity, he subtracted the mean luminosity value from the number 256. This gave a number for dye intensity, in arbitrary units. He prepared graphs comparing the dye intensity value obtained in this way, to show the effects of various pHs. The Y-axis of his graphs were labeled "Dye Intensity (arbitrary units)" and had a maximum of 256, or perhaps he divided the resulting numbers by 256 to get a percent maximum dye intensity. Either would work.

Paint chips are not ideal for comparison because there is no numerical indication of the intensity of the color. Pantone color sets have the same problem but have the advantage of representing a widely-accepted standard; unfortunately their cost is quite prohibitive. The human eye is actually extremely accurate at comparing two adjacent colors, as long as you do not attempt to use color memory to compare two colors that are not side by side. What would be best, if you do not have access to a program like Adobe Photoshop Elements, would be to get a more scientific to use to visually compare your different results. For example, look at the grayscale charts on the following page: 
http://www.oceanlight.com/html/about_color.html . As described there, one of the grayscale charts shows "0% (pure black) through 10, 20, 30, 40, 60, 70, 80 and 90% to 100% (pure white)". This is just what you need, if you cannot use a scanner or other optical device to digitize your results. If you use only one color of dye (be sure it's a single dye color, not a pre-mixed dye color containing more than one color), then you should be able to match the color intensity roughly, by eye, to the percent color intensity shown in the grayscale, allowing you to match a graphable number to each of your dyed test swatches of fabric.

Good luck with your project. 

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