IPA Recovery success

Any chemists here want to take a stab as to why this works?
I have been using Black exclusively for the past few months. I have a big order to fill and black is the preferred medium.

At the first wash cleaning, I drained the IPA into a 5 gallon bucket, expecting to try some things to clean it.
After neglecting it for several weeks, I opened the lid to the bucket and to my delight, the IPA was clean! All the black resin had settled in the bottom of the bucket! Tried it again with the same result.

I have another bucket that has mixed resin. Mostly Tough 2000 and Black, but it has yet to settle in the same fashion. In any case, pretty cool!

you can use a transparent bucket and this is going to cure the resin much faster, especially if you leave it near a window with a lot of daylight

Pretty sure this doesn’t indicate the IPA is no longer saturated with photo initiators or monomers…the Formlabs machines come with a hygrometer that you can use to check.

What’s likely happening is that the insoluble pigments in the black resin just settled and that’s different than the soluble things that actually dissolve and saturate the IPA.

AFAIK the “real” way to recycle solvent is to distill it. I know lots of people claim that leaving in the sun and skimming off the top works, but I’m skeptical from a chemistry perspective.


The bottle and sun method work, I do it personally and I reuse a lot of IPA. OK it will not be a 99% purity but I mix it with brand new IPA and it saves some cash. At the end of the day it does the job…

good explanation. Specific gravity seemed to match.
I do intend to use distilling for future recovery. I’ve tried the sun thing. It’s not for me.

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Specific gravity matched fresh IPA? That’s actually really surprising because I’m pretty sure the stuff that settled is just the pigment which isn’t soluble in IPA.

Did you wash a lot of parts in this, or is it still relatively “fresh”?

Once the IPA is saturated with resin, putting it out in the sun will produce a solid gel.

That has been my experience as well

Your comment is valid. This IPA had maybe 10-12 washes. Black tends to be very ‘dirty’ so the IPA may not have been as saturated. I’ve used that IPA for about another 10 washes and it is clearly not as effective.

Thanks for your comments.

Yeah I think there is a very common misunderstanding of how solubility works in these scenarios. I’d like to do some testing and make a video at some point for educational purposes.

Just because putting it in the sun produces a solid gel does not mean that the IPA is no longer saturated. It could be that the IPA has long past its saturation point, and there are now too many extra photopolymer bits floating around that cannot be dissolved by the IPA (ie. no longer soluble) and these will cure and harden or turn into a gel, but the actual IPA itself is still saturated.

That plus the pigments that you see which are not soluble which float and settle to the bottom make it easy for us to think that the IPA is “refreshed” when it really isn’t. Not to say that in this case the IPA cannot clean anymore…it’s possible that it’s still able to wash away resin because you’re dunking it in a liquid…but I would be surprised if it was as effective - and the only way I understand you can determine that is with a hygrometer.


I’d like to see a video to help educate more of the people as you see TONS of incorrect videos out there.

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I’ll add it to my list of videos to make :slightly_smiling_face:

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