Nixie - 14-1-2007 at 21:45
I got some white spots on my light-cream (undyed) cashmere sweater. Probably from bleach droplets getting on it accidentally. Can I just bleach the
whole thing to get it evenly white, or will it get wrecked or blotchy? I certainly cannot afford to replace the sweater.
Ozone - 14-1-2007 at 21:57
hmm. How strong was the bleach? I know that normal 5% will actually destroy cotton (as in ass-falling-out of pants, damage).
The cashmere is protein, so it may be somewhat more resistant; I would soak it (no dye) in a very mild reducing agent (cold, dilute sodium bisulfite,
for example). Then soak in water for a long while and wash (and cross fingers, toes, clench butt-cheeks, etc).
Hopefully there will be no holes. Unfortunately, the efficacy of any treatment method will be affected by the length of time since the exposure (if
the agent has done it's work...). This is true except in cases such as H2SO4 or H2O2 where the agent concentrates as it dries. Then--washing is
actually what finally kills it (the fabric).
As far as I know, you should generally avoid bleaching wool.
Disclaimer: I am male and have batch manufactured both pink and blue socks!
Best of luck,
O3
12AX7 - 14-1-2007 at 22:39
Yeah, H2SO4 and bleach do a number on cotton... copper too... I have former filter papers that have been around sulfates and copper compounds and the
stuff just falls apart after a few weeks/months of sitting. Probably also the reason why several of my shirts have light or black splotches or holes
in them, more or less front and center, not where something burning hot might come flying at me, for example. (I do, however, have some shirts with
holes in the shoulders, where hot embers rained down.) I also have holes in my jeans, roughly where I tend to wipe my hands off...
Tim
[Edited on 1-15-2007 by 12AX7]
Nixie - 14-1-2007 at 23:02
What about dyeing? I have some picric acid in storage. Is it safe for coloring fabrics? In my experience something stained leaches very slowly, so
I'm doubting that I'd poison myself, even though I wear the sweater on bare skin (cashmere goat and angora rabbit are of the few wools that actually
don't make your skin itchy...)
UnintentionalChaos - 14-1-2007 at 23:24
Hah! So thats where the light patches on one of my black cotton shirts came from....CuSO4 solution 
I never thought of it. Funny thing is that CuSO4 is used as a mordant (helps dye stick better) for natural dyeing
on wool or cotton. It makes white wool mint green and generally makes colors greener/browner. I guess it's mostly about quantity, as not much mordant
is used, despite boiling the yarn in it for hours.
I'm not too sure what would be wise to do here. The easiest solution is probably to dye the entire thing a brown or black which will cover up the
color differences. My only concern is that bleached wool does not dye as well as unbleached. You may have to spot dye afterward to darken the light
patches if they remain lighter. With a cream colored shirt, your chances of matching the color are almost zero.
Chlorine bleach dissolves wool even worse than cotton (I've tested this before. Wool yarn magically disappears into goop when thrown into full
strength bleach for a while. The bisulfite is a reducing agent, by action of released sulfur dioxide. Eventually, the wool will reoxidize and spots
will become a problem again. The other solution is of course, to oxidize the color. Typically this is done with H2O2 and should be done with fairly
low concentrations at low temperatures in an mildly alkaline solution (use Na2CO3 to raise the pH). Alkaline solutions are generally damaging to wool,
but it seems that the bleaching effect is increased substantially, enough to merit avoiding an acid solution.
PS: Concerning the post that was put up before I could post this, I would avoid using a chemical like picric acid as dye. I'd splurge for a few bucks
and invest in some RIT or other comercial dye. The point being that they are well tested as non-damaging to the fabric. Generally, urea is used to
help the artificial color soak into the cloth deeper, so good reason to invest in a new chemical/ break out the old stock. No offense, but even with
what I know about dyes, I would not just monkey with that costly a garment.
Best of luck.
[Edited on 1-15-07 by UnintentionalChaos]
Nixie - 14-1-2007 at 23:28
So how about a specific recipe to try? Can I use bicarbonate instead of carbonate? Say 1:10 dilution of 35% peroxide and half a teaspoon of baking
soda for a liter?
UnintentionalChaos - 14-1-2007 at 23:56
I looked around and found info like this:
1:16 dilution of 35% peroxide in water (by volume)
with 1/2 part (if 1 cup peroxide, 1/2 cup added) washing soda. I don't think baking soda affects the pH as much as washing soda, but heating the
baking soda will rapidly convert it to washing soda (carbonate). This was covered in some other thread. Wash the garment beforehand with hot water and
make sure the wool gets soaked through (this is standard practice in dyeing as saturated wool makes it easier for the solution to penetrate the
fiber). Heat the solution to 55C and add the garment. The garment should be submerged in the bleaching solution, so you'll need more than a liter,
unless you're REALLY tiny. Mix the garment around in the bath to make sure the bleaching mix is evenly distributed. Make sure to weigh down the
garment so it stays completly under. (Once I destroyed the color on a shirt while dyeing by not doing this, I never screwed up again) Leave 16-24
hours at temps of around 21C (a slightly warm oven with the door shut will work if you have a very large bowl and a cold house) For good measure, I'd
"swish" the mix around 2 or 3 times within this period to make sure the bleaching is even. Remove and wash in warm water. Soak for ten minutes in a
warm 1:20 dilution of household vinegar to remove any traces of carbonate and rinse again.
If this does not work, the problem either lies in the sheep, as some wool is more easily bleached than others, or the garment still as a lot of
natural oil on it. They sell wool-formulated degreasing soaps for this, but a shampoo (no conditioner) will work because it has a neutral pH which
wont damage wool.
I apologize for being long winded, but I hope everything works out.
[Edited on 1-15-07 by UnintentionalChaos]
[Edited on 1-15-07 by UnintentionalChaos]
Nixie - 15-1-2007 at 00:47
So I should shampoo the sweater first... BTW shampoo happens to be great at removing the collar grease stains from white cotton shirts ;P Conditioner
is also useful on some wool. I had to wash an angora rabbit sweater and it didn't like it, but conditioner restored it quite well (this is IMO the
best wool, since the hollow rabbit hairs are far better at insulating than other wools).
When you say 1/2 part soda, is that per initial concentration of peroxide, or diluted, or per 100% peroxide?
Now, since the initial spots were caused by chlorine bleach, do you not think I would end up getting a different bleaching on the rest? I wish I had
a piece of extra cashmere of this type to test different processes on it.
What about the oxyclean and and related products, or is that worse than peroxide? I'm just asking as any reasonable concentration of peroxide is
becoming harder to find and I try to decrease using up my 35% stash.
YT2095 - 15-1-2007 at 02:32
dilute H2O2 + ammonium (or potassium) persulphate is what I use to bleach wool fleece with before dying.
it doesn`t denature the material at all.
it`s interesting about the copper though, I`ve no idea why it does that, but iron sulphate (green vitriol) will do the same also but leave nasty brown
stains that look like shite, Oxalic acid will remove the color, but not the holes.
Picric acid I have used to dye wool fleece with too, it makes a great Acid Yellow, and if you did an entire garment in it I`ve no doubt you`de be
clearly visible from space even with a welders mask on 
Nixie - 15-1-2007 at 03:49
Well, yellow doesn't look too gay. Maybe I'll go for it. I don't have a source of persulphate, so I guess the peroxide and washing soda it is.
Ozone - 15-1-2007 at 11:18
Oxyclean (TM) and friends are either sodium percarbonate or perborate compounded with sodium carbonate (washing soda). What you get, depending on the
temperature (the pH is more-or-less fixed with the carbonate) is a slow release of H2O2. Essentially this is low-dose alkaline peroxide.
I still shy away from the thought of putting my skin in contact with a nitrophenol (regardless of how well it remains in the fibers). I have been
poisoned that way, and the amounts required can be very small.
Best of luck,
O3
UnintentionalChaos - 15-1-2007 at 13:13
per 1 part 35% peroxide, use 1/2 part washing soda. If you are going to use conditioner to restore it, wait until after bleaching (obviously).
Chlorine bleach is an oxidizer too, albeit a harsh one, so as long as you let the peroxide bleach to completion, there shouldn't be much color
difference.
If you wanted you could buy dirt cheap 3% by the liter and use that. You'd just have to adjust the ratios to make up for the massive amount of
water...about 2:1 peroxide to water by a very brief calculation (dont trust it). I can get 2 liters for 3 bucks or so, so I'd use that instead of the
35%
[Edited on 1-15-07 by UnintentionalChaos]
Nixie - 17-1-2007 at 23:14
The sweater has become stretched a bit, and I'm wondering if there's anything I can do to shrink it? Maybe something like felting?
Nixie - 19-1-2007 at 00:05
Success.