Acrylic crazing fail

I’ve known for a while that acrylic plus alcohol is supposed to lead to cracks/hazing, commonly referred to as “crazing”. I’d never actually seen it until now.

Here’s a cut piece of extruded acrylic.

Now I placed alcohol ink on it, thinking I might be able to get a stained glass effect. Like I said I had never seen crazing before, so I wondered if it were a myth. After about 20 seconds I noticed the cracks starting in from the edges.

The cracks were growing, slowly enough that I couldn’t actually see them propagating… but maybe I could? It was almost like I couldn’t believe my eyes. This is after it dried, the cracks may still be growing, I’m not sure.

I’m not sure if the fact that this is 0.118" extruded made any difference. I will say that the cracks seem to be starting from the overburn flashback spots, which makes sense in a way, the cracks will probably originate at weak spots.

So, uh… I don’t know who might need to see this, but there it is.


Yeah, and something as simple as a wipe with a lens cleaning wipe can do it.

I’ve kicked myself a few times. :frowning:


Well, there it is. I had never seen it before either. Thanks for that.
Imma experiment with some cast. I wonder if extruded has any internal stress on it.


Extruded vs cast acrylic have different stress. Extruded typically being higher. It does not take much for that stress to become apparent. Solvent being a big challenge for plastic with molded in stress.

In my youth, I was working on a disposable emergency resuscitation mask. Vinyl mask meets polycarbonate ( PC) molded core. the PC core did not stand a chance as all sorts of nasty chems were leaving the vinyl and finding all the molded stress in the core. Cracks everywhere. Solved it by switching to a rigid vinyl core and they go along happily ever after. I had ~10k PC cores headed for regrind. Back then they actually had a test where you dunked your part in a particular solvent for a set amounts of time to “quantify” how much stress there was. The longer it could hang, the lower the stress.


I wonder if annealing before applying alcohol would make a difference? It alters the internal stresses, right?


Hmm maybe. This was a goofy throwaway project though, so…

I just tossed a scrap into hand sanitizer. If nothing else needing it for Glowforge stuff means I had 3 liters or so of it about when it disappeared from store shelves. we will see if it creates detectable crazing in 12 hours or so. I have not seen it yet but am using some bulk brand rather than Purell.


I’ll show you a great example of crazing with acetone. I don’t have it with with me right now but I’ll post it in a bit.

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I assume this one?

You would change the nature of the crazing, but it would still craze. Alcohol attacks Acrylic. Don’t use Alcohol on Acrylic.

The extruded part makes me think that’s the key.

I’ve used alcohol and hand-sanitizer pretty much exclusively (and regularly) with acrylic, without any issues, but pretty sure everything I have is cast except for a mirrored piece I’ve not used yet.

I have found surface damage that can not be removed when engraving on unmasked acrylic, like “overspray”. Neither alcohol or abrasive won’t remove it as the surface itself has been damaged, it’s not a ‘deposit’ that can be removed.

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No, that was from the acetone in the paint. Below is a large edge lit piece that I made before I knew better. I engraved it with the masking on so there was quite a bit of glue stuck in the engraved areas. I thought I’d be clever and soak it in acetone. This is what happened after about five minutes.


Dang! Now that’s a good one!

Yeah, I was pretty shocked by how bad it was. I’m not sure if this was cast or extruded though. I still have a piece of it & I have some cast of the same thickness on order. As soon as it comes in I’ll do a test.

7 hours and no sign of crazing

Here is the result of my test. I did some digging in my shop and found a piece of the original acrylic with a label on it. It is definitely optix extruded acrylic. I had a scrap of proof grade cast acrylic so I painted them both with the same paint (The paint containing acetone that caused the severe crazing on my previous project) on one side. Below is the result.

So the paint with acetone doesn’t seem to be a problem at all on the cast acrylic.


The acetone gives your engraving a Halloween look. Spooky. :stuck_out_tongue_winking_eye:

From this and other mentions of the issue it doesn’t sound like it is consistent for all acrylic. Probably a good idea to test on a scrap of the exact material used before applying alcohol to the work piece.

It is now 28 hours and taking the plastic out of the hand cleaner and wiping it off is as pretty and clean as the day the masking came off

I have only seen this on the transparent flavors, not the solid or two color acrylic.
I don’t hose it down, just wiping any flashback burn off, but…