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How do we distinguish natural from synthetic dyes?
- By Price, Steve
- Published 20 March 2008
- Carpets
- Unrated
Price, Steve
Steve Price, collector of tribal arts and editor Turkotek; Tribal Art Forum; VCU's Department of
Physiology. In real life, Professor of Physiology at
Who cares, and why?
One of the questions that seems to keep coming up is, "How can someone tell whether a rug's dyes are natural or synthetic?" We might first ask why it makes any difference. Although most rug collectors agree that natural dyes are more attractive than synthetics, knowing whether a particular color came from a plant extract or from an organic chemical laboratory shouldn't change the aesthetics one whit. The real reason for caring is, or ought to be, that old rugs are worth a lot more than new ones are (all other things being equal), and knowing whether the dyes are natural or synthetic helps us estimate a rug's age and market value.
General methods for determining whether a dye is natural or synthetic
There are two broad classes of methods by which we can tell whether a color is of natural or synthetic origin. One is chemical analysis, the other is the so-called "experienced eye test" (a term coined, I believe, by George O'Bannon). Each has certain advantages and disadvantages.
Chemical analyses of dyes generally make use of some form of chromatography (a class of methods in which the chemicals in a mixture are separated from each other, their behavior during the separation providing information about their structure), sometimes combined with spectroscopy (basically, a group of physical methods for quantifying what our eyes identify as colors). Even the worst of these methods is more accurate than the "experienced eye" in identifying dyes, but even the best of them is fallible.
Offsetting the obvious advantage of being more reliable, chemical methods have a number of drawbacks. For one thing, they are expensive. The least expensive, thin-layer chromatography, could probably be set up in somebody's home for an investment of a few thousand dollars. The better methods, more sophisticated forms of chromatography, have startup costs in the tens of thousands. If spectroscopy is to be included, the cost of the laboratory will almost certainly amount to $100,000 or more.
In addition, being able to make use of these facilities requires skill and training. For most folks, being able to send samples to some centralized laboratory for analysis would be much more practical than setting up the equipment at home.
There are other disadvantages to chemical testing. Samples must be taken or sent to the testing facility and it will be some time (hours, at least, and probably days or even weeks) before results are available, a serious problem for a potential bidder at an auction or for what many dealers refer to as "opportunistic collectors". Since most rugs have 5 to 15 colors, a number of samples would have to be taken from each rug for analysis. And since each sample requires removing a little of the rug, we can't expect sellers to be too enthusiastic about the whole thing.
It isn't surprising that chemical analysis is rarely used. The "experienced eye" test is not nearly as trustworthy as chemical analysis, and is especially prone to the error of identifying some synthetic dyes as being of natural origin. Notwithstanding this problem, it has a number of advantages in practical situations. Nearly anyone can learn enough to have his own "experienced eye", at which point he has a testing system that is completely portable, very rapid, absolutely cost-free, involves no damage to the rug of interest, and is fairly reliable.
How can someone learn to identify natural and synthetic dyes?
There are a few elements of dye identification by eye that can be learned from books, but not from photos in books because color reproduction is so imprecise. The only way to learn is to be taught by someone who already has an experienced eye (that is, who has been taught by someone else with an experienced eye, and so forth back in time).
It's obvious that there is a danger that errors propagated from person to person can become accepted as truths simply by repetition. It's also a fact that there's so wide a variety of colors in both groups of dyes that educating our eye will require seeing thousands of examples under tutelage.
Where can we find people with appropriate levels of experience? And when we discover such people, how can we get them into a place with large enough numbers of rugs to provide specimens with which to educate us?
Knowledgable dealers can be very helpful, using their inventories as examples. However, it would be far better to have many teachers and many more specimens than any small number of dealers is likely to be able to show us. The two best places to go for education are rug conventions that include Dealer Fairs, and previews of sales at major auction houses like Sotheby's, Christie's or Skinner's. These provide the opportunity to see and handle several hundred to several thousand rugs in a single place, with the opportunity to discuss them and ask questions of large numbers of people who have some expertise. Collectors, dealers, and auction house staff are all potential teachers, and are usually generous with their time and knowledge.
Some rules of thumb for beginners
There's no way to develop an educated eye without looking at lots of real rugs and getting taught by people who already have some experience. However, there are some simple beginnings that can be made in the comfort of your favorite reading nook.
The issue of whether a blue color is natural or synthetic is moot. The natural dye used for producing blues is exactly the same chemical as the synthetic one, indigo. Indigo is even the dye of choice for blues in most contemporary fabrics, including blue jeans. One of the interesting things about indigo is that it doesn't dye the entire thickness of most yarns, but only coats the surface. Thus, when the surface abrades, the dyed part of the yarn is gone and its natural color peeks through. This is why blue jeans "fade". In fact, they don't. Denim has high and low areas; when the high areas abrade off, they appear white and the jeans look faded.
If you've struggled with grass stains on kids' clothes, you might be surprised to learn that natural green dyes are fairly rare. Some very early Turkoman pieces have a natural dark green in their palette, but most of the greens that are seen on rugs made prior to the availability of synthetic dyes are produced by consecutively dying the yarn with indigo and a natural yellow. These are usually easy to identify. Some natural yellows are very sensitive to light. In pieces using these dyes the color on the surface exposed to light will be blue while the back of the piece will show that it was once green. Another tipoff that a green isn't synthetic is that the surface of the yarn often abrades in some places, exposing yellow splotches amid the green (where the indigo layer has been worn off).
One of the questions that seems to keep coming up is, "How can someone tell whether a rug's dyes are natural or synthetic?" We might first ask why it makes any difference. Although most rug collectors agree that natural dyes are more attractive than synthetics, knowing whether a particular color came from a plant extract or from an organic chemical laboratory shouldn't change the aesthetics one whit. The real reason for caring is, or ought to be, that old rugs are worth a lot more than new ones are (all other things being equal), and knowing whether the dyes are natural or synthetic helps us estimate a rug's age and market value.
General methods for determining whether a dye is natural or synthetic
There are two broad classes of methods by which we can tell whether a color is of natural or synthetic origin. One is chemical analysis, the other is the so-called "experienced eye test" (a term coined, I believe, by George O'Bannon). Each has certain advantages and disadvantages.
Chemical analyses of dyes generally make use of some form of chromatography (a class of methods in which the chemicals in a mixture are separated from each other, their behavior during the separation providing information about their structure), sometimes combined with spectroscopy (basically, a group of physical methods for quantifying what our eyes identify as colors). Even the worst of these methods is more accurate than the "experienced eye" in identifying dyes, but even the best of them is fallible.
Offsetting the obvious advantage of being more reliable, chemical methods have a number of drawbacks. For one thing, they are expensive. The least expensive, thin-layer chromatography, could probably be set up in somebody's home for an investment of a few thousand dollars. The better methods, more sophisticated forms of chromatography, have startup costs in the tens of thousands. If spectroscopy is to be included, the cost of the laboratory will almost certainly amount to $100,000 or more.
In addition, being able to make use of these facilities requires skill and training. For most folks, being able to send samples to some centralized laboratory for analysis would be much more practical than setting up the equipment at home.
There are other disadvantages to chemical testing. Samples must be taken or sent to the testing facility and it will be some time (hours, at least, and probably days or even weeks) before results are available, a serious problem for a potential bidder at an auction or for what many dealers refer to as "opportunistic collectors". Since most rugs have 5 to 15 colors, a number of samples would have to be taken from each rug for analysis. And since each sample requires removing a little of the rug, we can't expect sellers to be too enthusiastic about the whole thing.
It isn't surprising that chemical analysis is rarely used. The "experienced eye" test is not nearly as trustworthy as chemical analysis, and is especially prone to the error of identifying some synthetic dyes as being of natural origin. Notwithstanding this problem, it has a number of advantages in practical situations. Nearly anyone can learn enough to have his own "experienced eye", at which point he has a testing system that is completely portable, very rapid, absolutely cost-free, involves no damage to the rug of interest, and is fairly reliable.
How can someone learn to identify natural and synthetic dyes?
There are a few elements of dye identification by eye that can be learned from books, but not from photos in books because color reproduction is so imprecise. The only way to learn is to be taught by someone who already has an experienced eye (that is, who has been taught by someone else with an experienced eye, and so forth back in time).
It's obvious that there is a danger that errors propagated from person to person can become accepted as truths simply by repetition. It's also a fact that there's so wide a variety of colors in both groups of dyes that educating our eye will require seeing thousands of examples under tutelage.
Where can we find people with appropriate levels of experience? And when we discover such people, how can we get them into a place with large enough numbers of rugs to provide specimens with which to educate us?
Knowledgable dealers can be very helpful, using their inventories as examples. However, it would be far better to have many teachers and many more specimens than any small number of dealers is likely to be able to show us. The two best places to go for education are rug conventions that include Dealer Fairs, and previews of sales at major auction houses like Sotheby's, Christie's or Skinner's. These provide the opportunity to see and handle several hundred to several thousand rugs in a single place, with the opportunity to discuss them and ask questions of large numbers of people who have some expertise. Collectors, dealers, and auction house staff are all potential teachers, and are usually generous with their time and knowledge.
Some rules of thumb for beginners
There's no way to develop an educated eye without looking at lots of real rugs and getting taught by people who already have some experience. However, there are some simple beginnings that can be made in the comfort of your favorite reading nook.
The issue of whether a blue color is natural or synthetic is moot. The natural dye used for producing blues is exactly the same chemical as the synthetic one, indigo. Indigo is even the dye of choice for blues in most contemporary fabrics, including blue jeans. One of the interesting things about indigo is that it doesn't dye the entire thickness of most yarns, but only coats the surface. Thus, when the surface abrades, the dyed part of the yarn is gone and its natural color peeks through. This is why blue jeans "fade". In fact, they don't. Denim has high and low areas; when the high areas abrade off, they appear white and the jeans look faded.
If you've struggled with grass stains on kids' clothes, you might be surprised to learn that natural green dyes are fairly rare. Some very early Turkoman pieces have a natural dark green in their palette, but most of the greens that are seen on rugs made prior to the availability of synthetic dyes are produced by consecutively dying the yarn with indigo and a natural yellow. These are usually easy to identify. Some natural yellows are very sensitive to light. In pieces using these dyes the color on the surface exposed to light will be blue while the back of the piece will show that it was once green. Another tipoff that a green isn't synthetic is that the surface of the yarn often abrades in some places, exposing yellow splotches amid the green (where the indigo layer has been worn off).