Commercial dyes are all labeled either Hot or Cold when you face them on the shelves. What does this mean? We explain the difference between a Hot and a Cold reactive dye.
What is the difference between a Hot and a Cold reactive dye? One would think it is quite obvious; the one is used with hot water and the other with cold. Almost every commercial dye available is labeled this way. Unfortunately, for the consumer who buys this product, this labellings is a little misleading.
A Hot reactive dye requires boiling at one hundred degrees Celsius for the bond with the fabric to be permanent. A Cold reactive dye does not need to be boiled, but its optimum temperature is still sixty five to seventy degrees. If you measure this heat with a thermometer, you will see that it is still steaming hot. I have burned blisters on my skin at that temperature.
The other misconception that people have is that they assume the Hot dye is more colour-fast than the Cold one because you have boiled the colour in. This is not so. Cold dyes are more robust and colours will remain brighter for longer than Hot dyes. The cooler process is not only a little easier, it is also more lasting.
Cold reactive dyes are very reliable and used throughout the global clothing and textile industries to permanently colour fabrics made from plant fibres. The dyes react with the fibre on a molecular level to produce a permanent bond that withstands wash after wash. The colour becomes part of the fabric.
A Cold reactive dye is, in my opinion, the most convenient by far for the hobby dyer.
It can be used to dye any fabric that starts out as a plant, i.e. cotton, linen, hemp and bamboo. Any fabrics with these bases will bond with reactive dye, e.g. denim, twill, calico, muslin, T-shirting, towelling, corduroy, cotton velvet, viscose, track suiting, poplin and cheesecloth.
Cotton/lycra and viscose/lycra blends also work well, providing the lycra content is under five percent. Reactive dye does not bond to lycra. Poly/cotton blends will only take the dye partially. The cotton fibres that run in one direction will take up the dye normally, but the polyester fibres that run in the other direction will remain white.
Because these dyes are used at high temperatures, expect your fabric to shrink.
The fabric is woven on a loom in the factory, where it takes its dimensions from the equipment. From there it is usually put through a stenter which steams the fabric into the desired dimensions for shipping. Sometimes there are variances in fabrics that come off the same equipment. Research has shown that such variances are caused by differences in the cotton fibres used. A fabric made from a crop that has had more water will behave differently from one that had less water in the field. Fabric stability is fibre-specific and will vary from one roll to the next.
Most cotton fabrics shrink about ten percent in the length. The width is usually stable to within one or two percent.
Published in: Consumer Information