Does anyone know why this is happening to my mirror acrylic? It looks like scratches but they are on the inside, not on the surface.
Any help is super appreciated! Thank you!
It is called crazing and has been discussed quite a bit here in the forum. You can search “crazing” and get an idea of what people have done to limit it. Did you cut shiny side up or down? What settings did you use? I have had pretty good luck with 1/8" mirror acrylic cutting shiny side up without the plastic masking some suppliers have on their material using Proofgrade acrylic settings.
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Thank you! I never would have thought up the word “crazing” to research it lol. I did cut shiny side up but I put a blue tape for masking over it & used proofgrade acrylic settings
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That doesn’t look like crazing to me. It might be flashback, but that’s not consistent with flashback symptoms exactly either. You can see evidence of flashback alone the edges (the regularly spaced “pits” in the edges are consistent with flashback), but the damage to the mirror on the rear looks different, almost like a defect in the acrylic. Have you peeled the masking off on a small portion to verify that the acrylic looks ok to start?
Crazing looks more like hazy areas that are filled with small cracks. Did you try to clean the acrylic after you cut it? Crazing can be caused by using the incorrect cleaning regimen.
There was a thread recently about avoiding flashback in acrylic by raising your material off the bed, I don’t have it handy, I’ll go look.
EDIT: Here it is- Suspended ablation
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Thank you sooooooo much! Exactly what I needed!
I peeled off the “seran wrap” type covering that came in the front of the acrylic & replaced with a blue tape (like a painters tape) for a mask & there is nothing on the back. I cut shiny side up, not from the back
And after you peeled the saran wrap off, did the mirror look ok?
@JessicaLee, if the defects are inside the acrylic and located away from your cuts, then I’m wondering if you simply got a bogus sheet of acrylic. Some of the marks appear to be biased towards the mirrored side, which could mean there may have been some debris present when the mirror finish was applied.
I’ve also observed the mirror finish delaminated by the incoming laser (mirrored side up), which is vaguely similar to some of the marks on your sample:
I haven’t devised a solution to the laser-induced delamination yet - perhaps cut in two, lower power passes
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Yup, no marks in it u til after cutting
I thought this may be a possibility because I cut some last week from a different sheet and it did not look like this at all 
I tend to cut shiny side down and haven’t seen this behavior. Might not solve your issue but maybe worth trying.
Don’t forget to flip your cuts before you try this, or the text will be backwards.
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Yeah might be a weird flashback or some sort of delaminating, though if it’s delaminating I would expect it to be concentrated next to the cut lines.
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I’m going to try upside down & cross my fingers lol thank you!!
Yup, you are right. Sorry I led you astray JessicaLee.
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I think it’s stress relief cracking. The acrylic wasn’t annealed and the cuts released random stresses in the plastic - it’s exacerbated by the mirror coating.
My nickel’s worth at any rate 
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You might be right, but isn’t that crazing? Crazing tends to look like a haze, hence the portmaneau of cracking and hazing [citation required, it may not be a portmanteau, unclear. anyway, get back on track Dave…].
If it is stress cracking, would you see that only in the surface mirror material? If you zoom in, the damage seems very superficial, it doesn’t appear to travel through the acrylic. I’m still thinking this is a surface damage caused by either the laser with some weird flashback, or by physical damage from contact with thesharp metal edges of the honeycomb.
I had some scrap mirrored acrylic and a blowtorch, so…
Just lightly sweeping the flame over mirrored back insta-created a haze in the finish, and a slightly slower sweep of the flame started blistering. Still doesn’t look exactly like what @JessicaLee posted however.
Heat seems to be the enemy of that mirrored coating. Not surprising, but a stark contrast to how well-behaved acrylic can be on its own.
I haven’t tried cutting shiny side down as @evansd2 describes, but I imagine protecting the mirrored surface with tape would be essential. Just speculating, but perhaps a paper-based protective coating might be a better thermal barrier than the plastic coating the mirrored acrylic ships with…
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I’ve had this happen and it seems to be the reflective coating heating up where it’s touching the acrylic. It seems some colors do it worse than other, but I could be wrong though and it’s really jut a WAG. I have really good sucess using these setting/method with mirrored acrylic on my Basic. Acrylic doesn’t vary much in structure and it all cuts generally the same so maybe run a little test cut to see if the crazing (or whatever it is) still happens?
I use a speed of 140 and 85 power with the mirror side up. I take the plastic masking off as it can melt and leave behind little balls of goo on the acrylic. You can put paper masking on both sides if you want to be really careful, but I usually just do the back (non-mirrored) side to prevent any flashback since even small marks can be seen from the front. If the cut lines are going to be covered, I don’t worry about masking at all if just cutting it.
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I second this! I’ve had this same problem with the iridescent acrylic available at Inventables/Canal Plastics. It looks exactly like @JessicaLee pictures. Not crazing but still, my assumption, damaging the film coating that gives the iridescent effect.
I’ve had good, consistent results using the same method that @kittski recommends here. Varying the speed and power and using a paper masking tape product on both sides (the iridescent acrylic is more transparent than the mirrored stuff).
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Crazing tends to be more localized to the causal agent (like chemicals, alcohol, etc) exposure. Stress relief cracking is usually pretty random following strain patterns in the plastic. You can see the strain lines visually with polarizing lenses or filters.
This is an odd material because it’s not homogenous - the mirroring is applied to the acrylic substrate so one, either or both could have weird strain patterns in the plastic.
Or it could be aliens. Aliens do that with their Ray guns 
This is one of those things I tend not to sweat about - figure an alternate way to do what I want and move on. I’d just switch to your way of cutting mirrored acrylic and move on 
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