Amy Gould and Matthew Polk on Radiocarbondating of Andean Textiles 2

On July 9, 2016, Amy Gould and Matthew Polk gave a Rug and Textile Appreciation Morning program here at the Textiles Museum in Washington, DC on carbon-dating of Andean textiles.

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Amy is a Graduate of Rhode Island School of Design with degrees in Fine Art and Architecture.

In 1983 Amy founded her own firm, Gould Architects, based in Baltimore and specializing in healthcare and institutional architectural services. Her client list includes many of the regions great institutions such as the National Aquarium, Johns Hopkins Medical System, the University of Maryland Medical System and the Baltimore Symphony.

In 1996 Amy was elected to the American Institute of Architects National Board of Directors and was elevated to the College of Fellows in 2000 for her leadership in the legislative arena.

She is a former Trustee of the Textile Museum and is currently serving as a Trustee of the Baltimore Museum of Art in Baltimore where she has chaired the Accessions Committee for AAAPI- Arts of Asia, Ancient Americas, and Pacific Islands.

Matt is a graduate of the Johns Hopkins University with a degree in Physics and is also a graduate of the Harvard Business School, OPM Executive program.

In 1972 Matt co-founded Polk Audio, one of the best known makers of high quality loudspeakers. He sold the company in 2006 and retired in 2008. From 2009 to 2011 he served as President of Gibson Island. In 2010 he co-founded MSI-DFAT Services which is the premier provider of acoustic testing services for spacecraft.

Matt is a former trustee of the Baltimore Museum of Art and currently serves on the Johns Hopkins Department of Physics and Astronomy advisory board and its executive committee.

Over the last 35 years their common interest in textiles has led them to create an eclectic collection which includes one of the nation’s most important groups of Andean textiles and Central African textiles along with significant groups of ethnic Chinese, Japanese and other Asian textiles. And, yes, more than a few nomadic carpets.

In 2009, as an outgrowth of their interest in understanding more about historic textiles, they established the Historic Textile Research Foundation, a 501-C-3, dedicated to creating a database of textile radiocarbon dating information for use by museums, scholars, collectors, dealers and other interested parties.

They began with an illustrated lecture.  Mostly, we are going to let the slides in it tell the story, with occasional additional comments.

You can see larger versions of any slide by clicking on it up to three times and you are encouraged to do that.

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Sometimes the age of an object is a subject of great importance.  For example carbon dating of the Shroud of Turin has been very controversial.  The results have questioned the authenticity of the relic causing some to question the validity of the Radiocarbon dating method itself.

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Nevertheless, the science behind radiocarbon dating is well accepted and most things are not so controversial.  When something about a piece doesn’t seem right carbon dating may shed some light.  In this case carbon dating showed that a textile believed to be Nazca was actually early Inca period with a red square added in the center using  old wool, presumably, from another piece to improve it’s marketability.

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Sometimes carbon dating can answer questions about how textiles were used.  Multiple samples from this central African Kuba Overskirt showed that it is composed of panels from 19th, 18th and possibly 17th centuries suggesting generations of owners modified and added to the piece.

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The textile traditions of the Hainan Island ethnic groups were virtually unknown outside China until the 1990’s.  Little research has been done into the origins of these traditions.  Carbon dating of this “Ghost Cover” showed that it was at least early 20th c. and possibly much older.

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When a piece is not like anything else carbon dating can sometimes help us figure out what it is.  Many who looked at this unusual piece thought I could be Sihuas, possibly as early as 200AD.  But the carbon date placed it in the early Inca period, 1420AD to 1449AD.  The two headed snakes suggest it was associated with shamanistic rituals observed by the Spanish conquistadors and still practiced today by Shamans such as the one pictured above.

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Carbon dating of groups of pieces can sometimes reveal important patterns.  Carbon dates on several dozen Andean textiles from the 1st millennium BC showed a sudden shift between 500 BC and 400 BC from painted, plain woven cotton textiles to colorful, wool textiles with motifs executed in complex tapestry, embroidery and knitting techniques.  How and why this occurred is still an unanswered question.

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And, of course, investigating these questions can be a great excuse for travel.  Our visit last year to the Temple of Chavin de Huantar (circa 1200 BC) on the Amazon side of the Andes in Northern Peru really helped us understand how the Chavin civilization exerted such a powerful influence over the entire region for more than 600 years.

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The answers to many other important questions lie in museums who have virtually no research funding.   Through our foundation we have begun a project with the Museo Nacionale in Lima carbon dating layers of Paracas bundles to understand whether these bundles were maintained over time by their communities.  The answers to this question will provide important clues to  understanding ancient Andean burial rituals and their culture of ancestor worship.

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Okay, just a joke.  But, the Radiocarbon dating technique is a quite modern development which has only recently evolved to become a really practical method for dating objects, such as textiles, where removal of only the tiniest amount of material for analysis can be tolerated. 

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Reduction of sample size and improved accuracy over the past 30 years has made it possible to apply this technique to many more objects.  Analysis is now possible with less than 10 milligrams of material meaning that samples can be taken from pristine textiles with no visible impact.

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The idea behind carbon dating is pretty straight forward.  Every living thing constantly absorbs radioactive carbon 14 (C14) in small quantities from the atmosphere.  As a result all living things have the same amount of C14 as their surroundings.  After death, however, the C14 is no longer replenished and starts to decay at a known rate.  If we measure how much C14 has disappeared from a sample we can calculate how long it has been since the sample was alive.

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But, nothing is ever simple.  When we analyse a sample today we measure how much C14 is left but because the amount of C14 in the atmosphere has changed up and down over time, we don’t know how much it had to start with.  That makes the determination of actual age a more complicated process. 

We start with the Conventional Radiocarbon Age (CRA).  This is how old our sample would be if the amount of C14 in the atmosphere had never changed and was always the same as it was in 1950.  The CRA is not the actual age of the sample it is just an approximation and the starting point for the analysis.  

  The amount of C14 in the atmosphere over the past 10,000 or so years has been determined by making measurements on tree rings of known age.  This ‘calibration curve’ can be statistically compared to the amount of C14 we measure in a sample today to give us a number of possible age ranges for the sample.  The analysis also gives us the probability that the actual age falls within any particular range.

This is the most difficult thing to understand about Radiocarbon dating and has led to many false impressions about how accurate or useful it is.

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For example, the CRA of this Hainan Island “Ghost Cover” is 82 years before present (BP)  +/- 20 years.  (We always use 1950 = the present.)  So, the CRA tells us this piece dates to  approximately 1868 +/- 20 years.

If we compare this result to the calibration curve we get the possible age ranges with probabilities:  1813 to 1919 at 69.7% probability and 1695 to 1727 at 25.4% probability.  The actual age could be anywhere in these two ranges.  We can say for sure that the piece is earlier than 1919 but could be as old as 1695.  Although this is not very precise it is still useful in telling us that this textile tradition dates to at least the beginning of the 20th century and probably 19th c.

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Sometimes what we know about a piece can help us narrow the range of possible dates.  The calibrated results for this early colonial era Andean textile were 1454 to 1529 with 47.4% probability and 1552 to 1634 with 47.6% probability.  But, the European religious imagery of the piece tells us it must have been created after the conquest in 1532.  So, the earlier date range can be eliminated meaning the wool used in this piece was harvested some time between 1552 and 1634 and the piece itself most likely made within the same time period.

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(click two or three times on the image above to get a larger version)

It’s always fun to test your textile instincts.  Without reading beyond the descriptions below take a look at the five textiles above and choose the one you think is oldest.  Write its number on paper.  Below is a more detailed description of each to help.

These five pieces have been carbon dated and span a range of nearly 2,000 years.  All are warp faced Andean tunics made of wool probably alpaca.

#1 is a beautiful, finely woven tunic with a light, very soft feel, made in two pieces joined in the center, with distinctive red wool stitching joining the sides.

#2 is a very heavy wool tunic made of thick, ropy natural color wool yarns with crude elemental brown stripes at the sides.

#3 is a classic Aymara marching stripe design.  It has discontinuous warps at the shoulder, often seen in pre-Columbian pieces, with a blue field on the other side.  The warp faced weave is very tight and slightly stiff.

#4 is a very soft, somewhat loosely woven tunic with an unusual trapezoidal form.  The edge bindings and neck treatment are beautiful multi-colored Inca style.

#5 has a nice floppy feel and makes extensive use of yarns spun in alternating directions creating subtle changes in surface texture to enhance the narrow pin stripe design.

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Done that?  OK, now, scroll down.

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We were shocked to learn that this heavy wool tunic was nearly 2,000 years old!  Utilitarian garments like this rarely survive this long.

Now, removing the oldest piece which of the remaining four is oldest:

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Again, write down the number of the one you think is oldest, the scroll down to see the carbon-dating-based answer.

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It was not surprising to learn that this adorable little tunic is nearly 1,000 years old.  The trapezoidal form is seen in a few pre-Columbian pieces but never, to our knowledge, in post conquest tunics.  Since making this presentation we have separately carbon dated some of the old repairs in this piece as having been made around 1750.  That suggests this piece was still in active use six to seven hundred years after it was made.

Now we are down to three.  Again, write the number of the one you think is oldest before scrolling down to the book answer.

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Again, not surprising to see that this piece is most likely to be Inca period and pre-conquest.  The two piece construction is often seen in pre-conquest pieces from the Arica area in Northern Chile.

The final two tunics are 250 years apart.  Write down your candidate for the oldest then scroll down to see the answer.

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Tunics and other forms of traditional dress were outlawed by the Spanish after the nearly successful rebellion of the 1770’s.  So, we can say with  that this  very sophisticated tunic is most likely mid-18th c. with some possibility it could be late 17th c..

Now, you may be wondering about the last tunic.

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We’ve included this piece to make the point that looks can be deceiving and that even quite modern pieces can be accurately radiocarbon dated.  The discontinuous warp and marching stripe design is characteristic of some of the most beautiful and iconic Aymara tunics of the 16th century.  Our instincts told us something wasn’t quite right with this piece but we really hoped carbon dating would prove that it was a genuine 16th c. tunic.  Unfortunately carbon dating results show that the piece is modern, most likely made between March and December of 1996 (72% probability).  This coincides with a revival of interest in traditional Aymara weaving in the early and mid-1990’s.  Whether it was made as a tribute or meant to deceive we will never know.

However, it does show that it is possible to carbon date very recent items, sometimes with great accuracy.  The signature of Atomic bomb testing after 1950 is immediately recognizable when analyzing a sample and can lead to a very precise determination of age.

Finally, here’s a quick summary of things to remember about radiocarbon dating.

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Also, Amy and I have established a foundation dedicated to building a database of radiocarbon dated textiles.  If you have any carbon dated textiles we’d love to include that information in our database.

Thank You!

Matthew and Amy then took questions on their lecture before moving on to discuss the pieces they had brought in.

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The pieces they brought included some featured in their lecture.

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They walked us through these in the wool allowing for treatment on different aspects.

I will treat them in the order in which they were arrayed in the room, not, necessarily in the order they were treated.

First were the five tunics from “Guess My Age”.  Here they are left to right, one at a time.  Matthew and Amy are speaking in the Comments.

AM1

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Comment on AM1: #1 is a beautiful, finely woven tunic with a light, very soft feel, made in two pieces joined in the center, with distinctive red wool stitching joining the sides and “evil eye” style rabette along the bottom edge.  Z2S yarns, possibly Vicuna wool.  As mentioned previously the two piece construction style is typical of pre-conquest tunics from the Arica area.

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AM2

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Comment on AM2: #2 is a very heavy wool tunic made of thick, ropy natural color wool yarns with crude elemental brown stripes at the sides.  A very rare example of a utilitarian garment that has survived for nearly 2,000 years.  Very beautiful in my opinion.

Detail of AM2.

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Comment on AM3: #3 is a classic Aymara marching stripe design.  It has discontinuous warps at the shoulder, often seen in pre-Columbian and conquest era pieces, with a blue field on the other side.  The warp faced weave is very tight and slightly stiff.  Although it looks just like a fabulous 16th c. tunic it is, in fact, modern and probably made in 1996.  The give away was the stiff feel and the Z3S yarns.  Genuine antique pieces are always Z2S or S2Z.  Nevertheless, it’s still a beautiful piece.

Detail of AM3.

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Comment on AM4:  #4  is a very soft, somewhat loosely woven tunic with an unusual trapezoidal form.  The edge bindings and neck treatment are multi-colored Inca style.  As mentioned before the piece itself is nearly 1,000 years old but we’ve carbon dated repairs to as late as 1750.  It is a well loved piece which has clearly enjoyed many, many generations of affectionate ritual use.  A very ‘honest’ piece and one of our favorites.

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Comment on AM5: #5 has a nice floppy feel and makes extensive use of yarns spun in alternating directions to enhance the narrow pin stripe design through changes in surface texture.  The combination of Z2S and S2Z yarns creates a herringbone effect in the surface of the textile that sets off the stripes.  Use of this technique along the edges is also said to allow the textile to drape without curling.  A great example of how the Aymara employ great sophistication in weaving to achieve subtle effects.

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Amy spoke to a textile on the right.

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Comment on AM6:  as mentioned earlier no one was really sure what this tunic was when it first came to us.  Carbon dating showed it was early Inca period.  But, it wasn’t until last year during a meeting with a Shaman in northern Peru that we began to really understand the piece.  His use of a snake motif staff demonstrated to us the ritual significance of the double headed snakes shown in this tunic.  Also of note is that the snakes are woven, not painted, employing an unusual displaced weft technique to produce the curving forms.

There was a textile on a tripod on the left.

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Comment on AM7: This is a Kuba Overskirt from what is now the Democratic Republic of the Congo.  The very fine weave and deep red color suggests it was  part of the royal family’s collection.  It is made of rafia palm fibers with many separate panels in a combination of embroidery and cut pile techniques.  By separately carbon dating six of the panels we determined that some panels were 19th c. while some were 18th c. and possibly 17th c suggesting it was handed down and modified by many generations of owners.

Details of AM7.

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There were two textiles on the front board.

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Comment on AM8: This so called “Ghost Cover” from the Li ethnic group of Hainan Island (South coast of China) is an example of the textiles used in funerary rituals.   During open air cremation a Ghost Cover such as this is thrown gently back and forth over the smoldering pyre.  Such use, although infrequent, is hard on these textiles. Few have survived intact and fewer still with a white ground.  

Little is known about these Hainan island ethnic groups who were so isolated that they did not even have a written language until the mid 1950’s.  The late 19th c. to early 20th c. radio carbon date for this piece and several others we have dated sheds some light on the ritual textile traditions of this area.

Detail of AM8.

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Comment on AM9:  This is the piece we talked about early in the presentation that when it came to us had a red square in the middle of the brown field.  

The dealer said it was Nazca which would have placed it in the range of 200AD to 600AD.  However, the  technique looked like classic Aymara warp faced weaving to us, suggesting that it was much later.  Also, the red square in the middle just seemed out of place and even without magnification one could see the cut ends of brown warps tucked back into the weave around the red square suggesting that the red yarns had been added later.  Carbon dating of the original brown warps placed the piece in the middle Inca period, 1450AD to 1500AD.  However, a sample of the red yarns from the center dated to 1220AD to 1280AD, 200 years earlier.  

It’s not uncommon to see old yarns from a very damaged piece used to repair or restore another piece. Here, it looks like someone used yarns from an old piece just to make the piece look more interesting.  This was probably done prior to 1980 after which the importance of early Aymara textiles was beginning to be appreciated.  After making this determination we had the red yarns removed and the area rewoven with matching yarns to restore the original appearance of the piece.  Ironically, today a genuine Inca period Aymara textile  is far more valuable than a relatively plain Nazca textile.

Detail of AM9.

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Amy and Matthew answered questions, on the pieces brought in 

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and brought their session to a close.

I want to thank them for yet another excellent session that was both interactive and authoritative.  Thanks to them also for making it possible to construct this virtual version of this program, and for their patient work in the editing of it.

I hope you have enjoyed and learned from it, too.

If radiocarbon dating and/or Andean textiles interest you, you can see another program of this sort that Amy and Matthew gave here at The Textile Museum a few years ago.

https://rjohnhowe.wordpress.com/2010/05/23/carbon-dating-for-andean-textiles/

Regards,

R. John Howe

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