I live in Brasil, and I never to listen about soda ash, nobody know the translation for it and I have many doubts about it. I used to fix the colours using a liquid quimical fixer to clothes. The colours stay for a time, but quickly lost your bright. Do you know how can I find soda ash in Brasil or the translation for it?

I am certain that you can find soda ash in Brasil. It is known by chemists here as sodium carbonate; the international chemical symbol for it is Na2CO3. It is NOT the same thing as sodium bicarbonate, or NaHCO3, which we use in baking cakes. A very common use for sodium carbonate is in swimming pools, to increase the pH. Sodium carbonate will easily produce a pH around 11, but the pH of a solution of sodium bicarbonate will not get much above 8.

However, sodium carbonate is only good for fiber reactive dye. What kind of dye are you using? Sodium carbonate is not very useful if you are using a hot water dye. (It is also not useful for fabric paint.) Most hot water dyes are never very permanent on cotton, and paints will wear off eventually because they sit only on the surface of the fiber.

In English we have different words for fabric dyes and fabric paints. Dyes combine chemically with the fiber. Paints contain a mixture of a pigment that does not, in itself, adhere to the fabric, plus a sort of glue to make it stick. Some dyes last much longer than paints, and dyes feel softer on the fabric. The very best dyes will last as long as the fiber!

The best dyes for staying bright, on plant fibers such as cotton, rayon, or linen, are the fiber reactive dyes. Some fiber reactive dyes work at room temperature (70 degrees F. or 21 degrees C.), and are called cold water fiber reactive dyes. Good types of cold water fiber reactive dye include Procion MX, Cibacron F, and Drimarene K. They are very easy to use, with sodium carbonate. I do not know of a source for buying any of these dyes in Brasil. (Please let me know, if you do!) If you want to try Procion MX dye, you can mail-order this type of dye from PRO Chemical & Dye in the US. They will ship internationally. Another type of fiber reactive dye is vinyl sulfone dye, also known as Remazol dye. This is a good type of dye, too, but it prefers higher temperatures in order to react with the fiber.

Your liquid chemical fixer might be sodium silicate, which also produces a very high pH. It can be used with any of the cold water fiber reactive dyes. Sodium silicate is recommended by the Tobasign people for use in fixing vinyl sulfone dyes, which they sell under the name of Tobasign dye. They call the sodium silicate "Tobafix". Tobasign is in Spain, and will ship anywhere. Expert dyers in the US say that the colors of this class of fiber reactive dye are brighter if the fabric is heat-treated with steam after the dye has been applied to the fabric; the process is much like cooking vegetables with steam, with a small amount of water in the bottom of a covered cooking pot, but for a longer period of time (30 minutes). Apparently it is also possible to use a high-pH chemical to fix this type of dye, but the results may not be as bright or as permanent as they would be if you steam the dyed items. This is the same type of dye that PRO Chemical & Dye sells as "Liquid Reactive Dyes", so you may examine their recipes. Their name for the high-pH liquid fixative is "PRO Fix LHF". They also mention "pot ash", which is potassium carbonate, or K2CO3. See "Vinyl sulfone fiber reactive dyes" for more information about this type of dye.

It is very important to understand which type of dye you have, so that you may select the right temperatures and chemicals for the dye reaction. See "About Dyes" for explanations of many different types of dyes.