To quote Paracelsus:
"It is not the substance that is poisonous but its concentration."
A low-impact dye is a dye that has been classified by the Oeko-Tex Standard 100 (an international certification process) as eco-friendly. Generally, low impact dyes do not contain toxic chemicals or mordants (which fix the dye to the fabric), require less rinsing and have a high absorption rate in the fabric (~70%). High absorption rates and a decreased use of rinse water create less waste water.
Fibre-reactive dyes are low-impact synthetic dyes that directly bond with the garment fibres rather than merely remaining as an independent chemical entity within the fibre.
* contain no heavy metals or other known toxic substances, and do not need mordants.
* are easy to apply and are available in a wide range of colour and wash-fast bright colours.
* fixation or absorption rate of low-impact dyes is at least 70%, creating less waste water runoff than conventional dyeing processes.
* are applied at relatively low temperatures (30ºC compared to the 100ºC needed for direct dyes), saving energy, and require controlled amounts of salt and alkali.
* the high cost of this dye becomes an environmental advantage, as it is cheaper to reclaim dye from its effluent rather than discharge it all and start from scratch. The water can also be recycled.
* the dye cycle is shorter than it is for other dye processes, meaning less water, salt and chemicals are needed.
* the entire process normally occurs at a pH of around 7.0, meaning no acids or alkalis need to be added to the water.
* recent advances have created fibre-reactive dyes with colours that are brighter and richer, and they provide excellent colourfast properties.
* like other environmentally damaging dyes, reactive dyes are made from synthetic petrochemicals.
* the process requires very high concentrations of salt (0%-80% of the weight of the goods dyed), alkali and water. Even if the unfixed dye is reclaimed, the effluent from this process can still contain high concentrations of salts, surfactants and defoamers, and are strongly alkaline.
* it's quite expensive, whereas conventional dye is cheap.
* the effluent normally contains salt, alkali, detergent and between 0% to 50% of dye used.
Natural dyes are often not at all low-impact, depending on the specific dye and mordant used. The extremely large quantities of natural dyestuffs required for dyeing, typically in a weight equal to or double that of the fiber itself, makes natural dyes prepared from wild plants and lichens very high impact indeed. Modern farming practices, where most natural dyes are obtained, require a remarkable quantity of petroleum fuels.
Many people turn to natural dyes because they are safe and non-toxic, so it is an important question to wonder whether the mordants that are used to fix the dyes are themselves safe.
Most of the mordants that are used for natural dyeing are common household materials, and are not seriously toxic. Alum, tin and iron are typical mordants used in natural dyeing.
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