In this lab you will be actually doing a chemical experiment as the fibers of the your garment react with the molecules of dye. The chemistry involved is actually relatively straightforward. The cotton fabric which is primarily cellulose will be soaked in a solution of Na2CO3 which is a weak base. This raises the pH to approximately 10.5 and creates an oxygen atom with only one single bond to the rest of the molecule, which is quite reactive: RXN1:
It is this open bond that wi1l chemically bond with the particular dye molecule. The example below shows how the cellulose interacts with a molecule of blue dye. RXN 2:
Tie dying is one of the oldest methods of printing designs on fabrics. Typically, parts of the fabric are bunched together in a design and knotted or tied together with string. Tied sections are protected from absorbing the dye and patterns are created.Excess dye molecules that have not bonded permanently are washed away using warm water rinse and a dye-carrying detergent.
After you dye
After you are done dyeing the fabric, leave it alone. Do not untie it. Do not hang it up to dry. Leave it tied up, and leave it alone. Let the fabric sit for 2-24 hours. The longer you can let the fabric sit, the easier it will be to wash out loose dye from the fabric. The length of time you let the fabric sit is not overly critical. If you are in a hurry, let the fabric sit for as long as your deadline will allow.
Wash loose dye from fabric
Wear gloves while handling the fabric, as the dye will still stain your hands until after it has been washed. Place fabric under cold running water and rinse until no more dye comes out of the fabric. We always say “rinse until you’re sick of rinsing.” A lot of loose dye will wash out off the fabric. This is normal. The wash water may turn black or brown, and the fabric may look discolored with ’dirty’ dye. This is normal as well.” After rinsing, move to washing machine. You may wash several pieces at once, up to a full load, even if washing different colors.
Use regular laundry soap in amounts for a normal wash load. Wash fabric as many times as you need to until you've washed out all the loose dye and the water in the rinse cycle is clear.
You are finished!
Wear your final product to the chemistry final for bonus points!