After hearing taking a class with Carol Soderlund (whose knowledge I greatly respect), I came home to run some experiments. I labeled three small pieces of fabric: dye supply, pool, and washing. I mixed up three gallons for dye activator using the same quantities: 1/2 of sodium carbonate to a galloon of water. One container consisted of the sodium carbonate purchased from a dye supplier, one from pH increaser from a pool supply place, and the last one from a box of washing soda (Arm & Hammer). Put all three samples in the same amount of dye stock (brown), used the same amount of dye activator, and they all batched the same amount of time. The results were very similiar.
Recently, I had some problems with excessive run-off/bleeding, especially with turquoise. Now I realize that turquoise is a problem child that needs warm temperatures and longer batch times. I wanted to re-test the sodium carbonate, using turquoise this time. Above are my results, they are very similiar. The mottling makes it a little more difficult to critically compare them. If you are wondering why I didn't use the third source of sodium carbonate, there are a couple of reasons. A recent bad experience, remember the excessive run-off I mentioned earlier. I have a feeling it was from a bad batch of sodium carbonate from a dye supplier. I had been using up the leftover little packets of soduim carbonate that had come in dye kits I had ordered for a class I had taught. After talking with several friends over the sudden problem, one of them mentioned that there had been a "bad batch" put out a couple of years before. I dumped all the sodium carbonate in my container (the little packets had mixed with other carbonate that I keep in a container) and started fresh. The problem dissappeared. Second reason, why pay for shipping cost when their are local sources. I encourage you to try the experiment. A box of washing soda is less than $5. Compare that to pH increaser or sodium carbonate from a dye suppier. Give it a try.