I agree with asking either the people who work with this stuff, the manufacturer(s) you have obtained your supplies from, or perhaps some jewelry makers whether they have any idea what can be causing the pink discolouration.
In the mean time I have been thinking myself about the pink hue of those feathers and the metal or metals that can possibly have caused it. I am absolutely no expert, but as far as I know, pure copper would not produce such reddish-pinkish hue. Pure copper oxidises to a dark brown-black (and turns green in combination with carbonate), which I think would leave it looking quite different from how it looks now. Copper reacting with acid seems an unlikely cause too as copper does not react easily with 'ordinary' acid. You would need a exceptionally strong oxidising acid (like concentrated nitric acid) and the result would be anything but pink: believe it or not, but blue (!) is a more likely outcome, again, not exactly in line with how it looks today. Besides, when would the dress have been exposed to acids -- especially this kind of acids -- anyway?
No, a much more likely explanation is that the metal in those pinkish feathers is not pure copper, but, for example, silver-plated copper. Silver-plated copper, when exposed to simple humidity (and provided the silver-plating is slightly porous), will oxidise to a deep red, a colour that looks much more like what we see in the feathers today. It is such a common phenomenon that it is also known as 'red plague'. It is interesting to note that the formation of only a thin layer of oxidation -- enough, quite probably, to stain the thread, though -- is actually already sufficient to stop the process. For what it's worth, 'modern' silver-plated copper wire often has a (clear) enamel finish to make it 'non-tarnish'.
Now, as to WHY silver-plated copper would have been used for those what seems to be carefully selected feathers I have absolutely no idea. I totally agree with the hypothesis that those feathers were treated differently for some sort visual effect rather than the result of simply using up some inferior supplies, but silver-plated copper would not have looked all that different (if at all) from the actual silver feathers, as far as I know, so this still remains a mystery ...
The rose gold hypothesis is an interesting one too because it certainly would explain the visual effect, but despite the copper content, rose gold does not really oxidise and tarnish or stain that much, as far as I know. Rose gold-PLATED metal of some kind might be different, though, but I have not been able to find any information on whether and how rose gold-plated materials oxidise/tarnish. For what it's worth, both rose gold-plated copper and silver wire are fairly common. I have also seen mention that the (modern?) copper version (sometimes? always?) has a layer of silver between the copper core and the rose gold plating to keep the colour 'true', so that DOES suggest that something MIGHT be happening to 'plain' rose gold-plated copper.
Thinking of high humidity and silver-plated copper, I can't help but wonder if the thread had already begun to react and tarnish, but perhaps not to the degree currently visible on the dress. Maybe it was like silk dupioni - today we see the slubs as interesting, but they were historically a sign of lower quality. The partially tarnished threads were just differently enough colored to create interest, without being a completely different material. And since it was destined for one wearing, perhaps they weren't concerned about how far the reaction would progress.
Yes, that was my (after)thought as well, actually: that the silver-plated copper somehow DID look different -- be it through oxidation already in progress or for some other reason -- different enough to be of visual interest, anyway.
The idea of the "acid" test was that it is supposed to simulate the effect of aging, not that the dress itself might have been exposed to an acid.
Yes, it's very likely that silver plated copper could have been used, it's documented that using copper as a base for silver or gold plating was a common approach to reducing the price of the stuff. But you're right, why, unless it looked different?
In the mean time I have been thinking myself about the pink hue of those feathers and the metal or metals that can possibly have caused it. I am absolutely no expert, but as far as I know, pure copper would not produce such reddish-pinkish hue. Pure copper oxidises to a dark brown-black (and turns green in combination with carbonate), which I think would leave it looking quite different from how it looks now. Copper reacting with acid seems an unlikely cause too as copper does not react easily with 'ordinary' acid. You would need a exceptionally strong oxidising acid (like concentrated nitric acid) and the result would be anything but pink: believe it or not, but blue (!) is a more likely outcome, again, not exactly in line with how it looks today. Besides, when would the dress have been exposed to acids -- especially this kind of acids -- anyway?
No, a much more likely explanation is that the metal in those pinkish feathers is not pure copper, but, for example, silver-plated copper. Silver-plated copper, when exposed to simple humidity (and provided the silver-plating is slightly porous), will oxidise to a deep red, a colour that looks much more like what we see in the feathers today. It is such a common phenomenon that it is also known as 'red plague'. It is interesting to note that the formation of only a thin layer of oxidation -- enough, quite probably, to stain the thread, though -- is actually already sufficient to stop the process. For what it's worth, 'modern' silver-plated copper wire often has a (clear) enamel finish to make it 'non-tarnish'.
Now, as to WHY silver-plated copper would have been used for those what seems to be carefully selected feathers I have absolutely no idea. I totally agree with the hypothesis that those feathers were treated differently for some sort visual effect rather than the result of simply using up some inferior supplies, but silver-plated copper would not have looked all that different (if at all) from the actual silver feathers, as far as I know, so this still remains a mystery ...
The rose gold hypothesis is an interesting one too because it certainly would explain the visual effect, but despite the copper content, rose gold does not really oxidise and tarnish or stain that much, as far as I know. Rose gold-PLATED metal of some kind might be different, though, but I have not been able to find any information on whether and how rose gold-plated materials oxidise/tarnish. For what it's worth, both rose gold-plated copper and silver wire are fairly common. I have also seen mention that the (modern?) copper version (sometimes? always?) has a layer of silver between the copper core and the rose gold plating to keep the colour 'true', so that DOES suggest that something MIGHT be happening to 'plain' rose gold-plated copper.
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Yes, it's very likely that silver plated copper could have been used, it's documented that using copper as a base for silver or gold plating was a common approach to reducing the price of the stuff. But you're right, why, unless it looked different?
So rose gold-plated copper? Very possible!
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