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Author Topic: white residue left behind from acetone  (Read 357 times)
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DougFunny
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« on: January 13, 2022, 03:59:25 PM »

I’ve always applied tissue in this manner: wet with spray bottle, blot dry with towel, then apply to pre-doped frame by bleeding acetone thru tissue. To this point, I’ve never really cared about the white residue left after acetone dries, it seems to go away when applying the finish coat of thinned dope. But, for curiosity’s sake, what is it and how could I avoid if I wanted to?
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philly
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« Reply #1 on: January 13, 2022, 04:47:42 PM »

I can only say I doubt the residue is from the Acetone per se', but perhaps it is leaching something out of the tissue or glue, and that is what gets left behind when the acetone evaporates. Said another way, clean/pure Acetone should not leave a residue.
Or perhaps you know that. Sorry.
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DougFunny
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« Reply #2 on: January 13, 2022, 04:59:57 PM »

Hmm yes on second thought maybe it’s the tissue? Seems to be the worst with Peck black or red…
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strat-o
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« Reply #3 on: January 13, 2022, 05:11:34 PM »

I think the water is the culprit.  The phenomena is called blushing.  It is some sort of reaction with the dope but I believe it goes away once the water evaporates (but it may take a few weeks).  To prevent it, work with dry materials and in a low humidity environment.
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Ployd
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« Reply #4 on: January 13, 2022, 07:05:07 PM »

Strat-o is on the money, water particulates trapped in the reactivated dope that cannot evaporate when the dope dries, common problem. I use a dope mixture that contains both acetone (to thin out) and butyl acetate to slow down the dope from drying too quickly, works a treat. Also solves the same problem when doping in high humidity conditions.

Ployd in OZ
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DougFunny
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« Reply #5 on: January 13, 2022, 09:29:34 PM »

Ah makes perfect sense! Thanks! Where does one find butyl acetate?
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lincoln
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« Reply #6 on: January 14, 2022, 11:29:01 AM »

I don't know if it's butyl acetate, but Sig sells "retarder" which I think is supposed to do the same thing{
https://sigmfg.com/products/sig-dope-retarder
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faif2d
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« Reply #7 on: January 14, 2022, 01:22:44 PM »

amazon has it

https://www.amazon.com/Alliance-Chemical-Industrial-N-Butyl-Acetate/dp/B085DJDBNN/ref=sr_1_3?crid=3OGWRCFQ9R0YL&keywords=butyl%2Bacetate&qid=1642184491&sprefix=Butyl%2BAcetate%2Caps%2C136&sr=8-3&th=1
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I used to like painting with dope but now I can't remember why!    Steve Fauble
ffkiwi
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« Reply #8 on: January 14, 2022, 02:38:18 PM »

Wearing my chemist's hat-the earlier responses are bang on-the white material is entrapped water-probably containing other trace impurities. The point about 'purity' made earlier is salient-acetone-being the excellent solvent that it is-and relatively benign-as far as organic solvents go-has widespread use across industry and commerce-everything from paints, glues, cosmetics, food etc.....this means the demand for it is vast-and naturally efforts go into recovering it from processes where it is used either for cleaning or some part of the manufacturing/processing-and not in the final product itself.

The upshot of this is that there is a wide range of purity available-and many processes do not require the acetone to be 100.0000% pure-so you get a range of acetones sold-some straight from the initial manufacture-others from reprocessing of previously used 'waste' stream sources. Most acetones available for commercial purposes are quite 'wet'-containing perhaps up to 15% water in some cases-this is why using acetone as dope thinner or to attach tissue to a previously doped surface is a bad idea...even using it for cleaning your doping brush is not the best-as you get the contaminants potentially left behind in the brush-to then be redissolved in the dope on the next occasion...

This is allied to-but not quite identical to 'blushing'-which can occur even with good materials, used under humid conditions....'blushing' normally being used to describe the white effect you get caused by water vapour being trapped in the dope layer-largely arising from the rapid evaporation of the carrier solvents-and the cooling effect that causes-resulting in the condensation of the water in the entrapped air.  Hopefully most of us know that the effect can usually be rectified by simple brushing of straight thinners on the affected parts   

 ChrisM
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TimWescott
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« Reply #9 on: January 14, 2022, 08:18:22 PM »

Acetone is a very "hot" solvent, in that it evaporates very fast.  This is almost guaranteed to cause blushing.  Basically, it's for cleaning tools.

It's better all around to use automotive lacquer thinner, or, if you want to be fancier than me, thinner that's the exact same brand as the dope you're using.  Use hardware-store lacquer thinner for cleaning your brushes and whatnot.

When you apply dope in humid weather, you may also want to add retarder, but again the best retarder is the same brand as your dope.

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Ployd
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« Reply #10 on: January 14, 2022, 09:27:01 PM »

ffkiwi said..
Quote: "using acetone as dope thinner or to attach tissue to a previously doped surface is a bad idea" If it is so, why have I been using that method more than 50 years without a problem?

Ployd in OZ
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ffkiwi
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« Reply #11 on: January 15, 2022, 01:18:54 AM »

You're sight impaired perhaps....and haven't noticed....?     There is a good reason dope thinners are a complex-and often proprietary-mixture of about 5-6 organic components...

 ffkiwi
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fred
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« Reply #12 on: January 17, 2022, 05:29:27 PM »

Stoopid Simple Glue stick applied on the Framework Works  V well to attach tissue. 
One can emulate the thinners on Dope reactivation trick By using Isopro Alcohol instead. 

No fuss No muss and FAR less toxic than Acetone .
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