It seems that the dye was lossely bound to the original clothing, but has bound much more tightly to my towels. There is no sign of the pink fading after several more washes.
Edit to add: I’m not looking for advice on how to get them whiter again, I can cope with pink towels! I am just curious as to why this happens.
In: Chemistry
It only takes a tiny amount of dye for us to pick up that the shade has changed, whereas for something to look vibrant, a lot of dye needs to be used – even if you washed the original clothing a thousand times, it most likely wouldn’t lose enough dye to become whiter than what your towels are now.
The tiny amount of dye can also very easily sit in the fibres of your towels where they’re more difficult to remove.
Ok. I like to dye wool so here’s how home dying works. I assume commercial dying works the same way but in larger amounts and with more caustic chemicals.
Animal or protein based fibers (silk for example) are very easy to dye—I dye them with food coloring or kool aid—and cotton/plant/acrylic fibers dont uptake dye in the same way so they require acid based dyes. I’ve never dyed with cotton/plant/acrylic so am not as familiar with that process but, from my reading, it’s fairly similar.
Fiber is generally soaked in a solution that makes it more receptive to the dye—for animal fibers that means a vinegar bath, which is just a couple glugs of vinegar in water. The fibers should soak in it until they are saturated. (This can take awhile because animal fibers tend to be good at resisting water. )
The fiber then has the bulk of the water squeezed out. Then dye is added to it. This can happen in a number of ways: directly into the fiber (ie sprinkle kool aid on the fiber) or via a water bath ( put the fiber into water and then add dye).
Then the fiber and water must be gently heated—via the sun, in a microwave, in a crock pot, in the oven at 200, on the stove, giant vat, etc.
If you do it right, the fiber will uptake most of the dye and the water will run clear —it will be exhausted. This is the goal because it means all the dye is in the fiber and—most importantly—stuck to the fiber. Allow everything to cool naturally. Then you rinse the fiber in room temp water. A fiber that has been in an exhausted bath will rinse clear almost from the get go.
If the fiber hasn’t taken up all of the dye, rinsing it will help remove all of the excess dye. If it refuses to rinse clear and that does happen, it’s a signal to put the fiber back on/in the heat in a water bath with acid to redo the heating process. Once the rinse water runs clear, your fiber is dyed! If it doesn’t, we say the fiber is bleeding. Because fiber works differently, the heat bath times and rinse amounts are different. Commercial dying doesn’t really take that into effect.
That’s what happened to your towels. Red is NOTORIOUS for bleeding and the dyer both added too much dye and then didn’t spend enough time allowing the dye to uptake into the fiber during the heating process or didn’t rinse it well.
So when you washed the red objects with your white towels, the red bleed, the white greedily sucked up the dye, and the heat and agitation of the machine helped set the dye. Because it wasn’t A LOT of dye, exhausting the water/dye/fiber was probably pretty easy. You accidentally dyed something!
RANT BELOW
Red is just a damn bitch. I once ordered yarn in red and white to make a baby blanket—color of dad’s favorite sports team. When I went to soak it before giving it away, my pan looked like a murder had happened and I had a pink and red baby blanket. Three days of soaking and rinsing and still murder in my pan. I mean completely red water, as if I had poured dye straight into the rinse pan. (I was kinda hysterical, honestly.).
I finally had to buy RIT dye set to make it stop. When I called the company to complain, the service customer person said quite snottily, “well. Everyone knows red bleeds.” After losing my shit on her—there bleeding and then there’s BLEEDING—I got a packet of replacement yarn that was definitely not red.
Anyway. There’s your explanation
So dye transfer can be caused by a bunch of stuff including excess dye left over from the manufacturing process, friction which can break down fibers and release dyes, washing in hot water which can break down the mordant and cause dye to leak.
Since the towels only got a little bit of dye there is no excess dye to leak off them, and if they were put in the dryer afterwards that would have heat set the dye. Over time they will fade due to friction/wear but it will take a long time because you only need a little bit of dye to change the color of white fabric. It could also be that the type of dye binds really well to the type of fabric in the towels.
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