May 10th, 2012, 09:51 AM   1
Marvin Amstey
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Default Wool corrosion from dyes

First let me thank Francesca for a very useful and informative essay. Secondly, I would like to ask whether any of the dyes or mordants used on these rugs were harmful to the wool like the iron used for black or brown in "western" rugs. I have a circa 1800 pillar carpet with what I have learned from this essay is dyed with sappanwood (or its like), in that the color has faded over time from a dark apricot to a lighter one. I have also noticed that the other colors - blue and white - are now higher than the apricot field color. I have attributed this to some type of corrosion. Any information about wool corrosion from any of these dyes or mordants would be appreciated.
Thank you again,
Marvin
May 11th, 2012, 12:09 PM   2
Francesca Fiorentino
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Wool corrosion from dyes

Hi Marvin

I have not great points about corrosion in your pillar carpet. And in general on Chinese rugs, if not for the wellknown corrosive effect of ferrous sulphate.

For sure the Tabibnia Gallery researches on Chinese dyes relating to a selected number of Ningxia and Peking from XVth to XIXth century, but mainly from an early date, as by catalog, don't report to corroded pile in the way of ferrous sulphate, but some in the way of a mechanical wear inside and on the pile.

I didn't find mention of apricot-like hues with a lower pile than other colours (nor white nor blue). Furthermore there is no mention to sappan mixed with that corrosive stuff.The bibliography quotes relates that "black and brown were obtained from tannin-dyes such as walnut, but also from a combination of gall nuts with ferrous sulphate, or even from logwood".

Something very clear came out from this scientific study: 1-Chinese dyers were really Master in obtaining very refined and particular hues, even changing in time. 2- Many vegetal sources, especially for yellow and brown hues, are still unknown.

Anyway I don't know anything about corrosive mordants.
I can suppose in the dyes of that apricot hue the presence of ferrous sulphate to darken it, or of some vegetal stuff containing a little part of ferrous compound (not rare in many leaves), or the apricot wool to have been bleached for any reason. Bleached wool is much less resistant than natural one.

So far in my possibilities

Kind regards
Francesca
May 13th, 2012, 09:01 AM 3
Pierre Galafassi
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Hi Francesca,

Warmest congratulations, your essay is excellent, clear and perfectly documented. We do need scientists on board of Turkotek, I am sure that Steve emphatically shares my opinion.
I like very much Moshe Tabibnia's scientific approach and do wish that all important and serious dealers would emulate him, even at the risk of contradicting rug lore from time to time.

Your conclusion that the Chinese/Ningxia dyers perhaps preferred sophisticated, delicate shades and were therefore ready to compromise with borderline lightfastness, when necessary to achieve them, seems highly credible to me.
It could also be that these dyers were more focused on dyeing textiles (silk for example) and less sensitive to the specific requirements of wool rugs (perhaps a secondary market for them), in terms of resistance to light-induced fading.

As far as the rarity of safflower yellow on rugs is concerned (while much used on textiles according to your sources), one could suggest that the Chinese / NingXia dyers were perfectly aware of its obvious, extremely poor lightfastness and judged it much too poor for rugs. Besides, the beautiful safflower red (which was known to Tibetans, thus probably to their Chinese-and Uyghur- neighbors too), has a much better lightfastness than the yellow component, but still an inferior one to madder-, lac- or cochineal (mordant-) dyeings.

That gromwell was found by the Bergamo team in purple shades is very interesting. Roots from this botanical family give very strong shades on wool, ranging from dull purple to purplish- or bluish grey and even black shades. However this strong dye must be applied either from a fatty emulsion or dispersion in water (no piece of cake), or from an alcohol/water solution (a trifle stronger than rice wine if possible (it would enhance the dyer's mood if it were more tasty too ), but this recipe surely was suspect to pious ulemas. The Bergamo finding might indicate that Chinese / NingXia dyers were not necessarily Muslims (Uyghur etc..).

If the Bergamo scientists have serious clues that a lac (mordant-) dyeing is showing an abnormal fading, I would suggest to them a determination of the mordant (by plasma spectra for example). Lac (lacca´c acid) gives a lightfast (Bordeaux-wine-) shade on wool when mordanted with alum, but I am not aware that the lightfastness with other mordants has ever been tested. It is perfectly possible that lacca´c acid would have poor lightfastness when mordanted with these metal ions, or of course when applied un-mordanted. The dyers may have accepted, again, what they saw as a nicer red shade despite its poorer light fastness. Tin- and zinc salts come to mind (copper and iron can be excluded, because they lead to brownish shades with lacca´c acid).

Vis-Rs is not a very selective method, even when backed by a complete data-base of reference curves and the ad-hoc software. As you rightly mention, it is only a useful auxiliary method.

Did your Bergamaschi friends already play with the fluorescence methods which are routinely used for analyzing pigments in old paintings by labs working with Museums? According to literature the fluo emission spectra of various mordanted madder pigments, for example, are quite specific.

Best regards
Pierre
May 14th, 2012, 05:35 AM   4
Francesca Fiorentino
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Hi Pierre,

Thank you for your kind congratulations: I just did a report of what is written in the beautiful Tabibnia catalog. The scientific team and who commissioned the job are the real addressee of them.
Regarding the presence of gromwell, it's possible I did not explain correctly, it was not found in these carpets, but in the related bibliography on Chinese dyes is quoted as a source for purple by S. Camman, The making of Dragon robes, from T'Oung Pao, Second Series, 1951, p. 297-351.
As purple they found only the Kerria lacca in the dragon cover, catalog 22.
About flourescence, X I suppose, I have no informations on its use in carpets analyses
I think in this case the scientific team did not use.

Best regards, Francesca
May 14th, 2012, 10:05 PM   5
Rich Larkin
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Thumbs up

Hi Francesca,

I agree it is an excellent and very interesting report about a category of woven rugs/carpets that is given less attention than it deserves. Do you have any information about the methodology that was used to establish the ages of the various rugs?

Rich Larkin
May 15th, 2012, 07:40 AM   6
Rich Larkin
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Hi Folks,

This tiger stripe mat is no doubt late in the range of rugs in the Tabibnia exhibition, but it appears to utilize a traditional Ningxia palette. It includes an interesting greenish-gray color I haven't seen in any other rug which shows significant corrosion.








The possibility has occurred to me that the stone green color could have been clipped low, though I doubt that was the case. However, there was a creative clipping effort elsewhere in the rug in the pale yellow border. One can just make out the remnants of a repeating swastika pattern within that border, created by selective carving of the tips. This technique was, of course, much more commonly used in later twentieth century Chinese rugs.

Another curious feature is the single line of black pile in the middle image. It occurs symmetrically on the opposite side of the rug (just about at the mid-point), but the color does not appear elsewhere. It is black, not blue, and appears to be original. It shows no corrosion.

Rich Larkin
May 15th, 2012, 12:29 PM  7
Francesca Fiorentino
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About flourescence, X I suppose, I have no informations on its use in carpets analyses
I think in this case the scientific team did not use.

Hi Pierre,
I would like to add that the abstracts of this scientific study will be edited in the next number of Hali.
The best, Francesca
May 17th, 2012, 07:16 AM   8
Francesca Fiorentino
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" Do you have any information about the methodology that was used to establish the ages of the various rugs?

Rich Larkin"

Hi Rich,
I am very despleased, but till now I have no informations about the aging methodology used of these carpets

The best, Francesca
May 17th, 2012, 10:36 AM   9
Francesca Fiorentino
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"This tiger stripe mat is no doubt late in the range of rugs in the Tabibnia exhibition, but it appears to utilize a traditional Ningxia palette............. ...Another curious feature is the single line of black pile in the middle image. It occurs symmetrically on the opposite side of the rug (just about at the mid-point), but the color does not appear elsewhere. It is black, not blue, and appears to be original. It shows no corrosion."

Hi Jeff,

I have right now seen a horse cover in Tabibnia catalog with the same motifs as your stripe tiger rug. It is a Ningxia, XVIIth cent., 98x138 cm. It shows the same field tiger-skin pattern with a circles vertical axis, the motif is in dark brown on a yellow mustard field. In the border appears the same pattern, usually called "diamonds", with two blue hues on an ivory back. By the catalog this motif is better a dragon "sliver skin" (I hope my English gets the right words) like in some Ming rare carpets, where flying dragons have this kind of skin (cat. 3A). It is also referrede that is a rare pattern as a border. The tiger motif is said to originate from Mongolia, well north of Ningxia region, but to have than become traditional in that crossway and trade center.
The old examples of it are referred by J. Mc Mullan (Islamic Carpets, Munich 1955) exclusively to Mongolia, on the contrary A. Hackmack, A. Lorentz, E. Concaro and A. Levi assign them to the refined weaving tradition of Ningxia region.

Your specimen appears to me well later, may be in the XXth cent. because of the vivid colors, the unusual greenish-gray, the clipping experiments. The strange black line could be a repair on a missing knots line: from the back every stripe has three little steps/line of knots. That black one looks the third missing. If not corroded it can be rather new, or/and dyed with a not corroding black stuff.

Regards, Francesca
May 19th, 2012, 10:25 AM   10
Francesca Fiorentino
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Ages of the carpets

"Do you have any information about the methodology that was used to establish the ages of the various rugs?

Rich Larkin"

Hi Rich,
as far as I understood from the detailed captions of the various carpets,
they have been compared and dated by the most exhaustive and recent studies on the subject, in particular M. Franses, H. Konig "Glanz der Himmelsshone Kaiserliche Teppiche aus China 1400-1750", Textile and Art Publications, London 2005, edited in occasion of the important exhibition in Koln-Germany. Further more M. S. Dimand "Oriental Rugs in the Metropolitan Museum of Art", Metropolitan Museum of Art New York 1973.
Some have been referred to important items already dated, carbon-dated too, holded in private a public collection.
Besides the carpets have been compared with other Chinese media (silks, brocades and porcelains) in particular with decorative devices featuring in Ming, Yongle e Kangxi period wares, much easier to date. The refineness, the symbolic power more or less present and the quality of the design were, as usual, the signs of closeness or distance to the models.
In the catalog there is a whole chapter dedicated to the similarities of contemporary porcelains.

Regards, Francesca
May 20th, 2012, 08:16 PM   11
Jeff Sun
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Quote:
Originally Posted by Francesca Fiorentino
"The tiger motif is said to originate from Mongolia, well north of Ningxia region, but to have than become traditional in that crossway and trade center.
Well, Ningxia is a a very Mongol area, and at one time the province was even merged with Inner Mongolia.

I have not heard of the Tiger Stripe pattern originating there. It is of course, much more commonly associate in Tibet and it, along with leopard spots, were used symbolically by people in power when the real hide could not be procured. Inner mongolian "Tiger" rugs that I know are all full portraits rather than an imitation of pelts, but this could also be a fashion that changes with the era.

Tibetans are of course familiar with the snow leopard and the tiger (from neighboring India mostly). Given the large buddhist pilgrim traffic back and forth between Tibet and Mongolia, I could easily see how the pattern could be transported as well. Of course, rugs in Ningxia were also made for the Tibetan (mostly ecclesiastical) market, so Rich's example rug could be one of those.
May 21st, 2012, 11:06 AM   12
Francesca Fiorentino
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Tiger skin

Hi Jeff,

I regret a lot about my inaccuracy relating on Tabibnia catalog.

I tried to attribute the tiger skin mat from Rich Larkin with some sureness to Ningxia province (tha's is not actually my job!).

In the catalog number 30 there is an horse cover with the same devices attributed to Ningxia. The question arised in the detailed caption was if there was or not a Ningxia production of such tiger skin patterned covers, or wether the province was only the trade centre of Mongolian items (thus relating J. Mc Mullan, A. Hackmack, and others opinion). In these terms the author says that in Mongolia the tiger skin motif was traditional because of the sciamanism. He does not assume that the motif in general originates from Mongolia (may be that is my relating fault).
As for this motif diffusion, it is well known tiger has been spread in the past from China to Anatolia. Further historical sources (Ibn Arabshah, "Liber Arabicus", and Marco Polo, "Il Milione") refer as tiger skin was a must of the imperial power among the Mongols since Genghis Khan reign and among the Yuan in China. It was not an exclusive Tibetan device. Moreover the Tibetan relations with Central Asia steppe tribes and hordes, thus with Turko-Mongol people seems really reasonable from Tom Cole analysis, where strong resemblances between "old" Tibetan rugs and Mongolian felts are shown.
Cole goes further relating of the many Tibetan tiger skin mats fakes (made to look old) woven for the market in the XXth, togheter with many tantric themes mats. But this is an other story...

So..returning to tiger skin device in old Chinese horse covers, by the author it could come from the near Mongolia, but became an usual pattern for horse covers woven in the province because of the high quality technical features. That assumption regards only the old Chinese rugs with this pattern, thus attributed to Ningxia.

Rich Larkin's rug has some links with a later Ningxia production.

Best regards, Francesca
June 13th, 2012, 10:02 PM  13
Rich Larkin
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Hi all,

I've taken the liberty of asking Jeff Sun, in another thread, to comment on the rug I posted here at #6. I hope that isn't too much of a breach of decorum.

Since I've never seen the unusual corrosive green/gray dye in another rug, I thought it was germane to this salon.

Rich Larkin
June 21st, 2012, 10:00 PM  14
Jeff Sun
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Quote:
Originally Posted by Rich Larkin
Hi all,

I've taken the liberty of asking Jeff Sun, in another thread, to comment on the rug I posted here at #6. I hope that isn't too much of a breach of decorum.

Since I've never seen the unusual corrosive green/gray dye in another rug, I thought it was germane to this salon.

Rich Larkin
Rich-

I'll help if I can, but I am not too much of a "Dye Guy" and I am sure Francesca and Pierre are better versed.

Nonetheless, I do have books, and I am prone to wild speculation...so here goes.

1. The blue green color: My guess is that it is some mixture of indigo. To quote Hallvard Kuloy from Tibetan Rugs pg 43
(a) Indigo can produce a very dark blue green color.

He also states on the same page:
GREY
(a) Natural wool

So maybe indigo dyed grey wool seems to fit the bill

Keep in mind that Tibetan rugs and "Chinese" rugs are not really the same and the dyers in Ningxia may have had other stuffs at hand...but indigo seems fairly universal among dyers.

2. The black stripes-I don't think there is anything symbolic here. I think perhaps they are a small repair with available materials, or perhaps the weaver ran out of the appropriate color at a crucial time and used a close substitute which didn't age the same.

3. Carving of symbols-Sure. Why not? As far as I know nobody had ever attached an age to the origin of this practice.
June 27th, 2012, 07:56 AM   15
Francesca Fiorentino
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Unhappy wool corrosion

Hi Jeff,

with my great regret me too is not at all a "dye girl" , so I leave the game to someone else (Pierre?).

The best, Francesca
July 10th, 2012, 08:47 AM  16
Francesca Fiorentino
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wool corrosion

Hi Jeff

regarding our corrosion subject I was remembering something like this occurred in the green dyed yarns used for the "celadon" hue in Farahan rugs from the last quarter of the XIX century. Copper sulphate was the responsible for color and later corrosion too.
May be in this Ningxia the same stuff was mixed along with some other dyeing material, because of the gray-green shadow different from the celadon one.

Regards, Francesca
July 10th, 2012, 04:22 PM   17
Richard Larkin
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Hi Francesca,

Thanks for that suggestion. I have wondered about the possibility myself. Sometimes, when assessing the green in a particular rug, I imagine I can see the color value of components of the color elsewhere in the rug, in the form of a blue and a yellow. Whether my judgments in this regard are good, I am not sure. In any case, I have tried to judge whether any of the three blues in the tiger stripe mat seem to be partnered with either of the yellow shades to produce that stone green color. If that were the case, though, it wouldn't account for the corrosion. However, if the dye process had involved the introduction of the copper element, as in the the celadon shade from the Farahan area, it might be a different story. I hoped someone interested in the subject of your salon might have some information about such a dyeing practice and result.

Rich
August 24th, 2012, 07:18 AM   18
Manfred Bieber
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Hi to all,
have you ever considered, that tin salts may destroy wool and silk fibres?
Regards
Manfred
August 25th, 2012, 10:04 AM   19
Pierre Galafassi
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Yes Manfred,

Indeed iron-, tin- and copper mordanting can wreak havoc with wool fiber, given the right conditions.

As far as iron is concerned there is no shortage of evidence for such a negative action, especially in the case of black-, brown and brownish violet-shades made with tannin/iron recipes: Hundreds of antique extant rugs prove enough the potential negative influence of iron/tannin.
Also seventeenth- and eighteenth century wool dyeing regulations in Europe (see for example Louis XIV's rules for "Grand Teint" in France) clearly indicate these limitations, while hinting at an iron-concentration-related effect.

For copper, I have found no convincing document so far, only credible but unproven assumptions in literature and haven't tested it myself seriously. Very small concentrations of copper in the mordant recipes actually seem to slightly improve the lightfastness of some (yellow) dyes, a fact which is also mentioned in books. My guess is that the effects on fiber stability, positive or negative, depend on the concentration of copper used for mordanting and on the quality of the post-dyeing rinsing operation. Do you have some evidences about copper?

For tin my curiosity led me to invest quite some work in my lab (about 50 dyeing operations under strictly controlled conditions of pH, temperature etc..), which has shown that, provided the dyed wool is properly rinsed and washed and the tin mordant concentration is kept small enough (say 2%wof or less), wool stability remains perfectly OK, while no particular harshness of the wool was detected, compared to a conventional alum mordanting (*). This fact was independent of the mordanting technique chosen (pre-,post- or co-mordanting). The wool stability was even OK after a (murderous) comparative lightfastness-test of over half a year on the sunny side of my roof, with testing temperatures reaching at times 60░C, test then followed by an artisanal rubbing-test.

(*) Of course the shade-change of a madder dyeing, when going from a pure alum-mordanting , to a mixed mordanting (alum/tin) and to a pure tin- mordanting is spectacular. But this is not our point today

Best regards

Pierre

P.S. What about your 1993 (excellent) work on fermentation dyeing, Manfred? Did you keep investigating this field? Sorry for being so persistent but I am genuinely interested.
August 25th, 2012, 12:22 PM   20
Manfred Bieber
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Hi Pierre.
thank you very much for your interest in my fermentation work.
You can get more information concerning wool and silk dyeing under:
http://www.exoriente.de/ background/natural dyeing.
Regards
Manfred