Dyes – synthetic and “natural” part 2

8 09 2009

After last week’s discussion, I think you understand why it’s important to remember that whether one uses natural or synthetic dyes a major concern is not only what type of dye the dyer uses, but whether the dyer has water treatment in place!    That’s because neither natural dyes nor synthetic dyes (plus the associated mordants, etc., used in the dyeing process) should ever be returned to the local waterways.  Even benign chemicals like potato starch will kill fish and other aquatic life because they encourage the growth of algae which depletes all available oxygen, among other issues (known as BOD or Biological Oxygen Demand).  And some so called “natural” dyes are themselves toxic.  So be sure to buy fabric from a supplier who has water treatment in place.

The other part of the equation is how the dye is formulated, because if toxic chemicals are used in the formulation then most of these chemicals remain in the fabric.  If synthetic chemical dyestuffs contain chemicals which can poison us, then the use of natural dyes seems to many people to be a safer alternative.  Additionally, the  question of natural dyes remains a romantic notion and is aesthetically pleasing to many people.  So what are natural dyes?

picture-1

Natural dyes are dyes derived from animal or plant material without any synthetic chemical treatment. They are obtained from sources like flowers, leaves, insects, bark roots and even minerals. The most common natural dyes (all from plants except cochineal, from an insect) are:

  • Madder
  • Cutch
  • Cochineal
  • Weld
  • Indigo

Contrary to popular opinion, natural dyes are  neither necessarily safer nor more ecologically sound than synthetic dyes:

1)      “Natural” does not mean safe – they are not synonyms.  Mushrooms can be poisonous. Arsenic is perfectly “natural,” meaning occurring naturally in nature.  Some natural dyes are almost perfectly safe; others are quite toxic. Some synthetic dyes are safe even to eat; others are too toxic to bring into your home.  A few  natural dyes, such as logwood, which contains hematein and hematoxlyn, are themselves significantly poisonous – they’re toxic whether inhaled, absored through the skin or ingested.  Indigo is a skin, eye and respiratory system irritant.  Proper health and safety equipment must be supplied when working with any dyestuffs and workers need to be trained properly so they treat the dyes and mordants with respect.

2)       Just because dyes are natural does not mean that they are sustainably or organically raised or harvested.   Pesticides, herbicides, defoliants, etc., may have been used on the crop or perhaps the crop itself may be genetically modified or irrigated unsustainably.   Extraction of madder is often done by dissolving the roots in sulphuric acid.  Sodium hydroxide is needed to produce natural indigo dye.[1]

3)      The physical amount of natural dyestuff needed to color fabric is much greater than that required by synthetic dyestuffs.  The amounts needed vary by dyestuff used and fiber type, but as an example, we have summarized the usage from an article in the Clothing and Textiles Research Journal[2]:

To dye 2 yards of upholstery weight fabric:

ounces

synthetic dye

0.7

freshly picked leaves

160 – 320

To dye 2 lbs of wool using:

ounces

low range

high range

Brazilwood chips

2

12

cutch

2

4

madder

6

16

To dye 5,000 yards of cotton fabric per month:

pounds

low range

high range

synthetic dyestuff

109

109

madder

938

2500

freshly picked leaves

25,000

50,000

4)      The quantity of dyestuff required is not a trivial consideration as the quantity of natural dyes that would be required to fulfill commercial dye demand would overwhelm  resources.  Some dyestuffs come from forest products, depleting valuable natural resources. Some can be wild harvested, but the population of creatures or plants required to fill human dye demand could not be supplied from current stocks of plants or animals.  (The third class of natural dyes, minerals, are most likely less objectionable in this regard.)  According to Ecotextile News (April 2009), it has been calculated that even if 2/3 of the world’s agricultural land was used to grow only natural dyes, there would scarcely be enough produced to dye the current volume of textiles.

5)    Natural dyes normally require much greater energy in the dyeing process as they usually require high temperature baths for longer periods of time than the optimized synthetic dyes; they also require a copious amount of the dyestuff itself as mentioned above,  and water.

6)      Natural dyes are less permanent, often requiring the use of mordants to affix the color molecule to the fiber.     Dye can sit on top of the fabric and look fine at first, but it easily washes out or fades to light very quickly.  The mordant creates a link between the dyestuff and the fiber – it remains in the fiber permanently, holding the dye.   That’s why cottons from India (where they had discovered mordants)  in the 18th century became so popular.  The mordant allows a dye to attain acceptable wash fastness. Some natural mordants exist, like pomegranate, salt and alum, but the more effective mordants are heavy metals (lead, mercury, copper, et al), which have unsavory toxicity profiles (see last week’s post).  Each different metal used as a mordant produces a different range of colors for each dye.

7)      A primary consideration in textile manufacture is that the color possibilities for natural dyes are far more limited than synthetics.   The color of any natural dye may be easily copied by mixing synthetic dyes, but the reverse is not true:  many colors are not easily obtained with natural dyes. The non-reproduction of some shades is a drawback in commercial production. The variability of the color makes the use of natural dyes difficult in any manufacturing situation where replicability of color is important.

The use of natural dyes will almost certainly make the fabric more expensive, firstly, because large quantities of land and raw material are required to obtain the same depth of color that could be obtained from a synthetic dye – although the amount of energy needed to extract oil from the ground and convert it into useable chemicals for synthetic dyestuff is probably very high, although I have not seen studies regarding this.   Also, both growing and applying the dyes are time-consuming –  natural dyes take typically at least twice as long as synthetic dyes to get a result, and using natural dyes on vegetable fabric will be more costly still, as vegetable fibers are more resistant to taking up good strong colors than animal fibers are, and slower, longer treatments often give better results.  So the question becomes one of social responsibility also – is it responsible to use land to produce ultra low yield dye crops for the benefit of those wealthy enough to afford them?

And then there’s the problem of availability: with perhaps the exception of indigo, the most common dyeing crop, crops grown for are dye are almost non-existent. A manufacturer would have extreme difficulty making vast improvements to the environmental impacts of their dyeing processes because the supply, and the infrastructure to apply it, doesn’t exist on an industrial scale.

And yet …  many people appreciate the slight variations caused by natural human methods and feel that it adds to the beauty and interest of a fabric.  The art becomes more important than the science.   They believe that there is a richness and depth to some of these natural dyes that a synthetic just cannot match.   A company at the forefront of using vegetable dyes is Rubia Pigmenta Naturalia .   They produce a dyestuff made entirely from the madder plant, which is able to cover 40% of the color spectrum.  They have completed a long term research program to increase efficienty, yield and handling of natural colors on wool;  the dye is exceptionally stable, homogenous, colorfast and grown and processed to organic standards.  In 2008, Rubia Pigmenta Naturalia was approved for use in Global Organic Textile Standard (GOTS) fabrics.

Another source of information is Natural Dyes International, which is a nonprofit organization  to research  natural dyes,  share information and eduate the public about the history of these dyestuffs.

Researchers at the University of Leeds are investigating new technologies using both natural and synthetic materials that may revolutionize the dyeing of textiles.  The first, a process that creates colored polymers inside fibers via a catalytic dye process,  has the potential to reduce the dependence on petroleum as a starting point for synthetic dyes, be more cost effective and lower environmental impacts.  The second is a natural/synthetic hybrid using a gene modification.  As Ecotextile News says,  “Nature alone can’t meet the technical or volume demands of the modern consumer, and petroleum technology isn’t sustainable.”  (But a genetically modified dyestuff?  Yet another blog posting, due in a few weeks.)

Having weighted all the options and looked at costs and prices, we decided that a fully optimized GOTS compliant synthetic dyestuff, applied in a facility that follows the GOTS water treatment standards, is the best choice for O Ecotextiles fabrics at this point in time.  We are always hoping that the industry will develop better choices as time goes by, because as mentioned in the previous posts, the GOTS and Oeko Tex requirements do not prohibit the chemicals that are so egregious in terms of toxicity, they just establish threshhold limits for these chemicals.  Again, the Europeans are at the forefront, with their REACH legislation which mandates finding replacements for up to 2000 of the worst chemical offenders by a certain date.  We’ll all benefit from their strong and forward-thinking leadership.


[1]http://greencottonblog.com/2008/06/natural-dyes-are-they-an-alternative-to-synthetics/

[2] Chen and Burns, “Environmental Analysis of Textile Products”, Clothing and Textiles Research Journal, 2006; 24; 248.


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2 responses

15 09 2009
india flint

this is a most interesting post. But once again [despite the abundance of published material available] I see that the genus ‘eucalyptus’ does not get a mention.

eucalypts contain everything in their leaves that is necessary to dye wool and silk [protein fibres] substantively using heat and water. the colours are entirely washfast and exhibit excellent lightfastness as well. there are over 1000 species and subspecies giving colours ranging from green through gold, orange, brown to deep rust red. further colour shifts can be obtained by using dye vessels made of various metals ie copper, iron, aluminium

in my work i re-use the water [used as the substrate for the dye bath] over and over again. the depleted leaf material is returned to the plantation as mulch. for visuals illustrating the colour potential please visit
http://www.indiaflint.com

i’m very much enjoying reading your pages [just balancing on the tip of the iceberg at present] and would be happy to engage in further correspondence on this matter – drop me a line through the contact page on my website if you like

10 02 2013
Ali

Thank you so very much for this post. As a textile artist and small scale clothier, I get lots of requests for naturally dying fabrics. While I’m happy to oblige my clients within a certain range, I’m not willing to sacrifice my health with more toxic dye processes, however “natural” they may be.

I’m certainly going to share this post with some of the more vocal critics, as I feel you have given excellent voice to the critiques that I’ve had.

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