A word of caution about the chlorine flame test

I’ve seen a number of people refer to this test when determining if products are laser-compatible.

I want to share a strong note of caution: there are many potential toxic byproducts of combustion. I believe this video only attempts to test for one. I would not rely on it to determine if a product of unknown composition is laser compatible or not.


Thanks for the heads up.

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Dan, while I 100% agree, I assume that most users are concerned more for the effects of hydrochloric acid gas on the inside of their GF, than the toxicity of the fumes issuing from the vent.
I’m in the fortunate position of being surrounded by 2 acres of grass, at the far end of a cul-de-sac, so toxicity is not one of my major concerns.


Yep. But his point is well taken. Firefighters will tell you combustion byproducts of carpet, drapes & upholstery = arsenic, cyanide and god knows what else - not necessarily in that order. :stuck_out_tongue_winking_eye:

Nice, me too, but @rpegg has us all beat.


Thanks for weighing in, @dan. I’ve edited my post from earlier today to reflect this info.


Shoot! I wanted to play with some green flames. :crazy_face:

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So really it’s all a matter of degree.
How much is produced by the vaporising of let’s say a total of 1 cubic inch of questionable material, (for example, 0.25" thick x 0.025" kerf x 15ft of cutting line) itself only containing a portion of the potential toxic producing compounds, compared with the total volume of a carpet of the same material, along with the rest of the furnishings ?


Absolutely. It’s the dose that makes the poison.

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The chlorine test is mainly to prevent damage to the machine, not for detecting poisonous substances, although HCL is poisonous as well as corrosive… The assumption being that if you vent outside it doesn’t matter if the material releases poisonous fumes. Even wood smoke is bad for your health if you don’t have a chimney and burning embers will poison you with carbon monoxide if there is no ventilation.

The big question is what poisons will the GF filter remove? HCN? CO?

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I hope not, your stomach is full of it… You reflux it all the time up your esophagus and into your lungs almost every night (it’s OK we evolved to handle that)


Oh no, what did I cut!


Hey @dan, I’m coming to this post after having received my GF (apologies if this has been answered already) and wondering if you or anyone else has an approved “chemical list” to avoid. I know GF has approved materials but I’d really like to get into testing all sorts of materials. Stone, Porcelain, all kinds of plastics, concretes,… literally anything and everything but I definitely don’t want to damage my machine… (sort of defeats the purpose).

Thanks for any input from you all. I love searching the forum!

He might not be able to answer that for legal reasons. :wink:

You should always research any new material thoroughly before you laser it.

Generally organic things are not a problem, but how they are prepared might introduce chemicals that you don’t want to be burning. (Chrome tanned leather versus vegetable tanned for instance, or pressure treated lumber, or some chemical in the finish or glue.)

Be exceptionally careful with plastics. If you know what it consists of, and know that the components are safe to laser, you can give it a try. If you don’t, test it, or don’t laser it. Some types of plastic release potentially deadly hydrogen chloride gas when they are burned. And PVC is a component of a lot of vinyls, which extends the list over into things like fake leather, moleskin, foams, and a lot of other products that people might not realize contain vinyl.

Use Google to find out whether something is considered generally safe to laser. Read the MSDS sheet if it is available. And if there’s still doubt, just pass on it.

Glowforge’s list of things that are not safe to laser is anything other than Proofgrade, or anything bought from a reputable established dealer of laser safe products as a laserable product. (Nope, not kidding.) :smile:

It’s why we talk about it in this section. :slightly_smiling_face:


Hey, thanks @jules! So are we saying that it’s the plastics and therefore
the Chlorine that is the thing to look out for? I would imagine that some
of the items I’m hoping to test may not have been studied yet so I’m
looking to find out what chemicals, when lasered, are harmful. Hopefully,
I’ll be able to look for these items in materials such as Concrete
mixtures, certain glues used in countertop manufacturing… things like
that. If you don’t have that information on hand do you know where I might
go to find out? Thanks again for your response! I’m always blown away by
this community!


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Yeah, definitely do not laser chlorine. (And I’m sure there are quite a few other things we wouldn’t want to laser either, but I’m still kinda new to this myself.) :smile:

I plan to avoid “ine” chemicals as a general rule. :wink:

Chemicals are your friend. The world is made of chemicals :wink:


It’s a matter of risk assessment. If you want to be super safe, just use Proofgrade. Next level is materials from a reputable source who are willing to claim they are laser safe.

More risk than that and you’re taking on some of the material understanding and how it behaves in a laser yourself. One way to go about that is to look at the MSDS (Material Safety Data Sheet). Unfortunately, the SDS’s are made for intended handling and may or may not give composition information. They will often give warnings for firefighters and there you might be able to tell what the hazardous combustion by-products are. One thing to note here is that cutting something with a laser can produce by-products in different amounts than combustion because of the way the we attempt to focus the heat in a tight a spot as possible and then cool it immediately. Some volatile combustion by-products that would not live long in a fire can survive the laser process and end up in the exhaust. As far as I can tell, this isn’t well studied actually.

Typical combustion by-products of carbon based materials (wood, plastics, leather) include some really nasty stuff to breath so you need to make sure you’re venting properly in any case.

And then there are the things that are bad for your laser (and can also be bad for you to breathe). So far, it appears that Chlorine is the easiest mistake to make since PVC is such a widely used material (often called vinyl). All of the other halogens (flourine, bromine, iodine, astatine called flouride, bromide, iodide, astatide in halide anion form) are also likely bad for your laser, used in materials much less commonly, but if you see them in the MSDS, definitely avoid.

And then there is stuff that just doesn’t laser well. They make a melty mess or aren’t really etchable or cuttable.

And then you’ve got reflectivity to IR light to worry about because you don’t want a specular reflection of the beam burning or etching something inside your Glowforge.

One resource that gets kicked around a fair amount here is the ATX Hackerspace list since it appears to have a pretty good list of stuff. I wouldn’t take it as definitive though since they aren’t particularly specific about which materials they tried or the source of the info, but it might be a good starting point: http://atxhackerspace.org/wiki/Laser_Cutter_Materials

Edit: some typos


Noooooooo! Refuse to believe I’m just a walking bag 'o chemicals. (Don’t burst my bubble here!) :smile:

edited original to limit the “bad” list to the “ines”.

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I saw what you did there, Jules, but just sweep up the mess after you.


By the way, I say “super safe” there, but there basically isn’t anything our laser cutters can cut that doesn’t give off toxic fumes. Heck, cooking food gives off toxic fumes. Most of these fumes, it’s dose that makes the poison. Which is why ventilation is so important.

Edit: don’t or doesn’t? Not really sure because my sentence structure is so wonky.

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