Sodium carbonate
Soda ash is the active ingredient in washing soda. The chemical name for it is sodium carbonate, chemical formula Na2CO3. It is more basic, that is, less acidic, than sodium bicarbonate (baking soda), whose chemical formula is NaHCO3. The purpose of sodium carbonate is simply to increase pH.
Hydration
Some forms of soda ash (e.g. that labeled as 'washing soda') contain more water molecules than others, which makes them weigh more and be larger for a given number of sodium carbonate molecules - this means that you need to measure out a larger quantity of the hydrated form in order to get the same results. If you buy sodium carbonate without the extra water molecules, then store it for several years in humid conditions, it will absorb some water and appear to lose strength, when in fact it has merely 'bulked up' and needs to be used in larger volumes. The type of sodium carbonate used in washing soda is a decahydrate, so you need to use a lot more washing soda than you would anhydrous soda ash, perhaps three times as much - assuming that you are able to find pure unadulterated washing soda that is suitable for use in dyeing. (In theory, we should use 2.7 times as much washing soda as a substitute for soda ash, if measuring by weight, or 4.6 times as much if measuring by volume.
What is soda ash used for?
Soda ash changes the pH of the fiber-reactive dye and cellulose fiber so that the dye reacts with the fiber, making a permanent connection that holds the dye to the fiber. It actually activates the fiber molecules so that they can chemically attack the dye. (It can also be used with silk, but not other protein fibers such as wool.
Do we need to use soda ash with Rit dye?
No, soda ash will not make all purpose dye, such as Rit® or Tintex®, permanent on the fabric. Instead, you must either use a washfast dye such as Procion MX dye, which does require soda ash, or use a commercial cationic fixative in order to make all-purpose dye acceptably washfast, so it does not bleed in the laundry forever.
How do you use soda ash with Procion MX and similar fiber reactive dyes?
There are three choices, depending on what you're doing: add the soda ash before the dye, add it with the dye, or add it afterwards.
1.Adding the soda ash before the dye is the usual method for tie-dye. First tie the garments, or leave them loose. (It is all right to put slightly damp garments into the presoak solution.) Make up a solution of 1/2 or 1 cup of soda ash per gallon of water (soda ash dissolves best in warm water, 96°F. or 35°C.), and soak the material from 5 minutes to an hour, depending on your recipe and materials. Then, wearing gloves, wring out the material, and prepare to apply the dye. (Optionally, you may chose to line-dry your soda-ash-presoaked garments, for some dyeing techniques. The soda ash stays in the fabric. Be cautious, as the dust can be irritating to breathe or to the skin.
2.Adding the soda ash with the dye is commonly used with dye painting. A possible drawback is the fact that the dyes will retain their ability to dye fabric for only a few hours after the soda ash is mixed into them. (Procion MX dyes without soda ash will stay good for at least a week after mixing, at normal room temperature.
3.Adding the soda ash after the dye is the usual method for immersion dyeing and low water immersion dyeing
Is there any alternative for soda ash?
In dyeing cotton or any other cellulose fiber, such as linen, rayon, tencel, hemp, etc., the requirement is simply to increase the pH (alkalinity) of the reaction to somewhere around 10.5 to 11; the exact ideal pH depends on the fiber being used and the individual dye color.
