We bought a hobby laser machine for leather and in trying to find out about safety, I came across the table of materials on this forum about materials that can and can’t be cut/engraved. I did some research of my own about chrome-tanned leather and made a video about it. I refer to the comments in the table in the video and hope the video sheds some new light on this well-worn topic
It’s interesting to hear the science behind chrome tanned leather. As I understand it, it doesn’t cut/engrave as well as vegtan leather, but would @Team_Laser consider removing the material restriction?
As I always understood it, the problem with any leather that isn’t veg tanned specific is that no one knows what kind of things are used in it and lasering an unknown cocktail of potentially toxic chemicals is generally a bad idea.
I don’t really see a problem with allowing it, because I know it already happens a lot. We can bring it up at the next meeting and talk about it.
If I remember correctly the answer is no.
It has a higher potential of damages of lasers.
More importantly deadly cyanide gas can be created.
Lets error on the side of caution and not.
This is what i remember I’m sure some one more educated then myself may have facts and opinions that we as a committee could entertain.
The answer has historically been “no” based on not knowing what could potentially happen.
That’s why I appreciated the video above that actually goes into the science.
That music is amazingly annoying.
Emphasis added…
The results indicate that for investigated samples laser engraving does not affect the concentration of hexavalent chromium and are in accordance with EU requirements
What about cutting? Given my personal experience with lasering leather I can say the time, temperature, and power are much higher. How does that effect the concentration of hexavalent chromium? Was cutting included in the study (but excluded from the abstract)?
What is that concentration of hexavalent chromium? Zero? Way beyond a reasonable level? What amount of that becomes airborne? Is the Dallas Makerspace ventilation adequate to clear the hexavalent chromium?
Regardless of that, it took 15 seconds with Google Search to determine that chrome-tanned leather can also include chlorine compounds.
Can you explain it by typing it out, given that Talk is a written forum and all, or are you just trying to drive views to your YouTube channel?
This was my very first thought when I first noticed this thread.
The guy registered barely 10 minutes before he posted this and hasn’t been back since or at least he hasn’t posted any responses or further information.
He probably is trying to get views…
But also calls out DMS directly and our listing it as a banned material as part of the reason he did the research.
For those that don’t want to watch the video, I’ll rewatch it tonight and post notes.
As the originator of the “freaky chemicals like chromium” phrase (that I expected to be edited out by someone and replaced with a more professional sounding entry), I’ll pitch in a minute. The gist of the video is that this person states they have education in chemistry, and operating interest in a business that personalizes leather goods, for which they use a CO2 laser. As such, they did their own digging and using their own chemistry background, concluded that chromium tanned leather sold by reputable dealers in most “1st world countries” (my phrase, not theirs) will contain little to no hexavalent chromium as they are tanned with salts of chromium in the trivalent form. Then they go on to quote a study conducted in 2021 that shows scientific evidence that the lasering with a CO2 laser of chrome tanned leather which used the trivalent form of chromium salts to tan (which is ~ ‘all of them available for purchase by reputable sellers’ - my words, not theirs) does NOT substantially increase the presence of hexavalent chromium. In other words, per that study and this person’s opinion, there is not an appreciable gain in the carcinogenic chromium variant for having lasered chrome tanned leather with a CO2 laser.
I do think the question of “the study talks about engraving; what about cutting?” is relevant, and would love if OP addressed that here.
Otherwise, draw what conclusions you will from the study (I assume the link I posted above won’t paywall, but I don’t really know…) and/or our summaries of the video, or just go watch and read for yourself.
As @trapezium stated, should make lively discussion @ the next laser committee meeting. 
Thank you @jast for the accurate summary and engagement with the content of the video. I appreciate it.
In response to the question “the study talks about engraving; what about cutting?”, I don’t believe it will make any difference. While one can use a higher power (or slower speed) to cut rather than engrave leather, I actually find it works better to go over the same path twice or three times. This is like subjecting the leather to more than one laser pulse which is what they did in the study I mentioned. This allows the laser to burn the leather at deeper layers but it’s the same chemical reaction either way. Here is the point: the reaction is a combustion reaction which means the leather is combining with oxygen and burning. The power of the laser will not change this reaction.
As I mentioned in the video, to convert Cr (III) to Cr (VI) requires a redox reaction which only happens under specific conditions. For the trivalent chromium to oxidise (lose electrons) to the hexavalent form, there must be another agent available that can be reduced (gain electrons) since this type of reaction (red-ox) happens in pairs. From what I have read, these conditions are when the ions are in an aqueous solution, at a certain temperature and pH. It cannot happen when you simply burn the leather with a CO2 laser.
I can’t help but notice that you’ve ignored the last question. The one which would involve chlorine gas.
Brian I’m not a chemist, so take my research with a grain of salt (also a chlorine compound - sodium chloride).
So the gentleman above is Dr Bruce Kloot. He’s an engineering teacher at University of Cape Town. He also does laser leather projects commercially via Coupe & Couture.
As Jast and Bruce have already posted, I won’t rehash what they said. I did learn though that hexavalent chromium (Chromium 6) can be found pretty much everywhere including tap water. The US doesn’t regulate Chromium 6 in water directly just overall Chromium levels.
Chrome Tanning though is many different processes and chemicals. For those interested here is a synopsis of some of those processes via the Central Leather Research Institute (Government of India site) CSIR-Central Leather Research Institute
Bruce does mention in his video that cutting synthetic leather is particularly dangerous.
Regarding the chlorine… the only thing I’ve seen mentioned is sodium chloride (table salt) and something called perchlorates. Was one of these what you saw?
Perhaps laser should adopt a burn test like in this hackaday article to test if a particular material is safe?
Hi @Brian and thanks for your engagement with this topic.
I did not ignore your last question. You made a statement so I did not see the need to respond: “Regardless of that, it took 15 seconds with Google Search to determine that chrome-tanned leather can also include chlorine compounds.” (emphasis added)
The reason why I have added the emphasis above is because of the difference between the terms used in this statement and your last one that refers to it: “I can’t help but notice that you’ve ignored the last question. The one which would involve chlorine gas.”
As I pointed out in the video, there is a difference between the element chromium and the salts of chromium with the element taking on different properties as the salt. To illustrate this I referred to sodium, which is a very reactive metal, and sodium chloride, which is harmless table salt.
The same can be said for chlorine. Chlorine is the element but the naturally occurring state is chlorine gas, Cl2. As I said in the video, chlorine gas is poisonous. However, chlorine compounds have a variety of properties and are not necessarily toxic or dangerous. I mentioned two in the video, both of which are chlorides. Hydrogen chloride (HCl) is a gas that should be avoided since it combines with water to form hydrochloric acid and can burn the throat and lungs when inhaled. Sodium chloride, however, is harmless as already mentioned.
In your second statement you wrote, “The one which would involve chlorine gas” but it is not necessarily true that, even if chrome-tanned leather included chlorine compounds that it would produce chlorine gas when burned with a laser. The chlorine compound might decompose into chloride ions, form HCl or form a number of other compounds given that it would probably be bound up with the tannins if it is present in any appreciable quantity in chrome-tanned leather.
I would be interested to read the resource that you found in your Google search because one of the most common misconceptions about chrome-tanned leather is that it is the same as synthetic leather and produces Cl2 gas when lasered. As I mentioned in the video, synthetic leatherette (which contains PVC) should not be lasered because it produces HCl gas (I found a number of sources claiming that it produces chlorine gas [Cl2] but I could not find any chemical reaction indicating this). But neither HCl nor Cl2 is produced when chrome-tanned leather is subjected to laser treatment.
I would also be interested to read the resource that @JoshW draws on in an earlier post to claim “More importantly deadly cyanide gas can be created.” I suggest that this is hearsay from someone confusing chrome-tanned leather with synthetic leather which contains a form of polyurethane. Once again, as I mentioned in the video, there is a chemical reaction that produces large quantities of hydrogen cyanide (HCN) when PU leather is burned with a laser but the same is not true for chrome-tanned leather.
Exactly. You don’t know. Neither do we.
The study you cited is based on leather from a single reputable manufacturing. The leather is not dyed. It’s not treated beyond tanning with chromium and liquors. There is no doubt it is reasonably safe to use as stock with a laser cutter.
This is our reality…
We have members that fetch discarded material from dumpsters. The provenance cannot be known. Is that leather safe to laser? Who fucking knows. It could be treated with plasticized PVC to protect it from moisture and stains. The bright pink dye could turn into highly toxic gases. The fire retardant, which is required by law if the leather was used for furniture, could turn into dioxins when cooked.
So, @jast including “chromium” in his statement…
…was a mistake. But his characterization is spot on for our makerspace.
This does not improve the quality of the conversation or your argument.
What I am challenging is the notion circulating on the internet that all chrome-tanned leather is toxic and therefore should not be laser cut or engraved. There are all sorts of ideas out there that cannot be traced back to a scientific argument. I am trying to get to the bottom of this by the little knowledge of chemistry that I have. I’m sharing it with this forum because of your table of substances that can and can’t be lasered which I found since it is publicly available on the internet. I would think it would be in the interests of DMS to ensure that the information that it provides to the rest of the world is accurate.
You mentioned that a 15-second Google search allowed you to determine that chrome-tanned leather can also include chlorine compounds. You later changed this to chlorine gas. My point was that even if it does contain chlorine compounds, this is not necessarily dangerous and probably will not release chlorine gas. But I don’t know - you are correct - because I haven’t established whether your claim is accurate. If you can provide the link, I will have a look and investigate whether it makes sense scientifically and what the dangers are. But the odds are that people are confusing chrome-tanned leather with synthetic leather and throwing around terms so that people who are not confident enough to check the veracity of the source will just accept it. If it’s not carcinogenic hexavalent chromium, then it’s a freaky chemicals like cyanide gas. I have some ideas about why this is happening which I won’t go into here.
But I do appreciate the sentiment of your post. There are dangers and I am not advocating that everything should be allowed because people’s health and safety is a serious matter and should not be put at risk. But allow me to suggest - considering that I am not going to be using the laser machines in your makerspace - that it doesn’t make sense to have a published set of guidelines that has a blanket ban on chrome-tanned leather while, by @trapezium’s own admission “it already happens a lot” in your makerspace? Further, why ban a category of leather based on the tanning process when, according to what I’ve found, it’s actually not the form of chromium used for tanning that is the issue?
Neither do fallacies.
The alternative is to only allow chromium tanned leather from reputable vendors that includes no additional treatments including coloring. At a makerspace that is not capable of enforcing that restriction.
You suggested HCl as a by product. Even if our ventilation removes HCl in it’s entirety, how much damage will that cause our equipment? (No need to answer. We already know.)
By focusing entirely on leather from a single reputable manufacturing.
Toxicity is only one part of the equation, though. DMS’s lasers are (usually) well ventilated, so even lasering PVC (NOT RECOMMENDED AND WILL PROBABLY GET YOU BANNED) would (maybe) probably not harm the user. It might very well harm the laser, though.
Materials aren’t just on the banned list because of harm to the user, they’re on there because of harm to the machine. You might not kill yourself with off-gassed chlorine compounds, but they might harm the optics and cause downtime. Makerspaces aren’t as much fun if people laser things they shouldn’t and the lasers are down for a week, even if the people walk away with a healthy set of lungs.
This is definitely true. I guess the question is, where do we find a reputable source of information on the potential damage. The maker/vender? I would think maybe they’d know definitively whether something would damage their product?
Re: rules we can’t enforce. Honestly the space is full of rules we can’t enforce and there isn’t a good way to change that. 
we can however mitigate the damage to machines, by asking the people who do follow rules to not cut materials that may damage the machines.