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Old October 27th, 2018, 11:15 AM   #3
Pierre Galafassi
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Join Date: Oct 2009
Posts: 87
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Rich, your bottle-throwing skills are admirable. This one even went up the Rhine River landing in front of my house.

Hi James,
Nice rug!
You probably have identified the criminal all right: Saxon blue.

A bit of doubt remains though, which only a proper analysis could eliminate: You are puzzled by the lack of evidence for poor lightfastness. And right you are.

That leaves us with 3 possibilities:
- Either your rug passed most of its years in an obscure wine cellar (Not a bad choice, I would too)
- Or the rug was woven less than a couple of decades ago. Some very ancient synthetic dyes are still manufactured today in local 'cottage-factories' . I would not bet the house on Saxon Blue having yet disappeared from even the most remote Asian bazaars.
- Or the blue is not Saxon blue, but another ( synthetic-) dye sold on the market, created for another end-use, but misused for rugs. The most obvious candidate fitting the profile (Blue dye with rather poor wet-fastness but good light-fastness on wool) would belong to the amino-anthraquinone family which offers clear violet, blue and blue-green dyes. The family contains dyes with good light-fastness and with either low-, medium or high wet-fastnesses. Dyes of the former type (so-called migrating ‘acid’ amino-anthraquinone dyes) appeared on the market during the first decades of the XX century, some are still manufactured in pretty large volumes (a business of over 10 million $ )and used by the textile industry, for example for wall-to-wall polyamide carpeting.

Thanks for the ref. to the excellent paper authored by de Keijzer and al.
They make a note which could be of high interest for ruggies: They mention the 'corroding' properties of Saxon Blue. An occurrence already noted by some Turkotekers in the past.
Perhaps a comment could be useful here.
Saxon blue is produced by so called 'sulfonation' of indigo, a jargon which means that indigo is reacted with sulfuric acid, leading to the introduction of 'sulfonic' groups in the indigo molecule and giving it a good solubility in water (and a lousy affinity for wool, hence the poor wet-fastness).
This new molecule, once 'isolated' (purified), has no detrimental effect for the wool structure whatsoever. But, during the XVIII-XIX centuries, chemistry was still in its infancy and Saxon blue producers were not necessarily aware of the fact that the dye powder which they were selling still contained lots of impurities, one of them being residues of sulfuric acid, which of course would attack the wool fibers during the dyeing process and even after it.


About cleaning of traces of bleed. Sorry James, I can’t give any good advice. Except one, don’t even dream of doing any wet treatment.

Best regards
Pierre
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