I make beaded jewelry, and I occasionally use clear stretchy string. At least, it starts out clear. I constantly have to adjust or redo parts of my work, and by the time I’m done, the most vigorously used (don’t know if it’s the friction or the stretching) parts of the string will have taken on a noticeably pink hue.
What kind of weird reaction is going on? Why does clear polyester (I think it’s polyester) turn, of all things, pink? (And what search terms does one use to find out what a string is made of?)
Since you’re making jewelry that needs to be repaired, I’m assuming you’re wearing it. In which case, what you’re probably looking at is dead skin, or possibly a chemical change in the poly due to contact with your sweat.
According to JoAnn’s, it’s made of “plastic,” which doesn’t help much…
Trace amounts of the carotenoid Lycopene. It’s a hydrocarbon, insoluble in water but seeps easily into soft plastics. The source would be transfer from food (it’s what makes tomatoes red).
[ETA: I see you say it’s unworn jewelry, so presumably not this, unless it’s from your hands while you’re manipulating it.]
Methylobacterium can produce a pink-stained biofilm in damp places, and likes to colonize the soft plastic surface of PVC.
ETA: I see now another ref that says it may be Streptoverticillium reticulum.
It’s an issue with PVC on boats, apparently.
Plastic that is stretched will change molecular conformation enough to be easily measurable with a spectrometer. The stretching actually could subtly change the long complex chains and type/amount of intermolecular cross links. This could easily change the way light interacts with the molecules.
While I don’t know about this particular case, it’s a common party trick to show that the stretched out sides of polyethylene in two liter bottles is different than the non-stretched portion by the lid
I used to be a spectroscopist
OP hasn’t said whether the color is on the surface, or throughout the plastic. If it’s throughout the plastic, I think it must surely be what Sigene describes.
The OP can see here for more Photoelasticity - Wikipedia. In her case the stretching is sufficient to trigger permanent deformation which locks in the color effect. She’d probably find different colors if she stretched strands of the same material of different diameters.
Sorry, haven’t had much time to get to my computer in the last couple of days. Sigene’s answer sounds like it fits. (Oddly enough, I’ve made a couple chokers this week with a different brand of elastic thread, and there’s been no pinking. I guess they made it differently).
And thanks for the welcome back.
[QUOTE=Washoe]
(Sorry, I couldn’t resist. I just had to make an ossicle of myself.)
[/quote]
