Laser-Etch Stainless with Only Plaster & Alcohol

Many hobbyists and hackerspaces have the $500 Chinese 40W lasercutters which most of us know are about as successful at etching metals as a featherduster is at drilling. [Frankie] and [Bryan] have figured out a way to use the laser to chemically activate an etching process. See experiment part 2 as well.

First, to be clear, they are using a quality 40W Epilog Zing, not the cheap one, but40W is40W. They mixed the plaster (calcium sulfate) with Isopropyl until it resembled white ketchup. After either thinly painting or airbrushing the material onto the stainless surface (both worked), the mixture is dried with a heatgun then put into the laser. 100% power and 5% speed was what worked for them.

The result was an engrave with a noticeable bite. Something they claim had no effect at all without the mixture.

Stainless steel is an alloy of iron and some chromium – not the same as chrome-plated steel. [Frankie]’s explanation of the chemistry is that the surface layer of the stainless is a transparent chromium oxide. With the heat of the laser, the calcium and chromium swap dance partners. Calcium takes the oxygen and chromium takes the sulfate. The calcium oxide washes off but the chromium sulfate causes the etch.

Next time you’re at your local space, give this a try.

31 thoughts on “Laser-Etch Stainless with Only Plaster & Alcohol

    1. That was the first thing that went through my head so I contacted him and asked before I wrote the article. Since the laser is only required as a heat source, and since the reaction is chemical not thermally-ablative (like normal laser etching), he figured it wouldn’t have any effect but didn’t try.

      Do it, write it up, and send us a tip if you do. I’m curious.

    2. Hi Guys

      I have done some fine markings with my 60watt laser on any metal using cheap galvanizing spray in a can . It sits real well on the surface and does not buff off at all . work like a charm

  1. OK, I’ll have to try this. I’ve used Cermark to varying results, including a couple competitors, it never seems to be worth the cost. The kind that worked the best came in a spray can, I couldn’t brush it on. I think we’ve used air brushes and auto spray guns to some success.

    1. I’ve done a bunch of experiments on our 80 watt laser.

      Instead of Cermark, try using a can of dry moly spray librucant (spray molybdenum, high temperature lubricant) from the auto parts store. It works about as well and is a lot less expensive. The laser sinters the moly into the surface of stainless steel – it won’t come off short of scratching the metal. The unexposed sections come off with Acetone. Use high power and slow speeds (100%, 3mm/s, and adjust as needed.)

      I can actually cut thin sheets of stainless with our laser, but it burns the edges. It doesn’t work too well unless it’s an extremely thin sheet. We can make thin metal gaskets, but thicker stuff doesn’t work. Take apart a feeler gauge and see how thick you can cut. I got ours to cut up to 0.01″.

      I’ve also been able to cut copper plated boards – both the top layer and completely through a double-sided PCB, but again it’s too ‘burny for anything useful. Place Kapton tape over the copper layer, this causes the laser to interact with the copper.

      My current experiments are with poly-acetate nail polish. Put a thin layer on just about anything (such as PCB material), then ablate off the pattern for a printed circuit, then etch. This also doesn’t work well, because the smallest spot size for our laser can do is 20 mils. :-( It might be useful for artistic etch resist, though, and it should work on just about any metal.

      And if you’re just looking to make marks on metal, try anodizing the metal first. Especially Aluminum – the laser knocks off the anodized surface, letting a clean aluminum pattern show through.

      There’s a lot of area for exploration with laser cutters. I’d be interested in anyone else’s “secret sauce”, if they’re willing to share…

        1. I’ll try for more layers tomorrow – thanks for the suggestion.

          I don’t know how the Moly reaction works. I was told that it “sinters” into the metal, which indicates that it’s not a chemical reaction. Perhaps the heat of the laser melts the top layer of steel and the moly soaks in.

          1. Another possibility is that the moly and the stainless form a eutectic mixture lowering the melting point of both. If that’s the case then you won’t be able to build up layers unless you find a way to spray a thin coat of stainless and then alternate between moly and stainless layers.

          1. Well since it’s not listed, clearly it means 5% of absolute max speed of course. 14 989 622.9 m / s. This is good for your laser, the relativistic effects will actually reduce wear relative to the observer.

            I asked the author what laser he had so people could look it up themselves. It’s a 40W Epilog Zing. I would have looked into the software and speed settings myself to give physical units for you all… but I was writing the article on Christmas morning.

            *cowers under the community whip*

  2. Ive used cermark on an epilog 30w @ my hackerspace. Luckily I got the spraycan for free to etch something on an axe for someone. Ill have to try this method and see the results hopefully will be a cheaper alternative

  3. Before everyone gets excited by the use of the term “etching”, I would be extremely hesitant to suggest that any etching is going on. “Etching” implies that you’re chemically _removing_ the metal, which is not what’s happening.

    Marking products like Cermark/Thermark work by either melting the compound and having it stick to the surface, or melting the surface slightly as well and forming a mixture. For this reason, Cermark/Thermark contain a mixture of both metal oxides and glass/glazes, to promote adhesion to a range of different substrates. The patents are well worth a look at – some numbers are 6075223, 6852948, 6855910, 6313436.

    A wide range of materials will work in place of Cermark – I’ve had good success with the molybdenum disulphide trick on stainless steel. I’ve also used plain pottery glazes on ceramic tiles (apply the glaze, but don’t fire it – use the laser to mark it) and they work quite well.

    The laser is easily capable of melting the surface of the metal (even though it can’t cut through). This will then combine with whatever you have on the surface (which has also been melted, more than likely) to form probably a rather complex mixture of metal oxides/carbonates or whatnot.

    I just did a quick test with the plaster/isopropanol mixture and have put some pictures up here:

    IMG_4682

    Yes, it does leave a very effective dark mark, but it’s level with (or even slightly above) the surface of the original metal. That bluish etching I did without any plaster, just to show that the laser can melt the surface slightly.

    Power was 40W CO2, raster speeds from 100mm/s down to 20mm/s, and a raster stepover of 0.05mm.

    Unfortunately, the dried plaster has very poor adhesion; the first coat I put on got blown off by the air assist on my laser!

    1. I’d also like to add that there are known examples of laser-assisted etching, unfortunately I can’t remember or find any of them at the moment. From memory, they consisted of the metal piece placed in a bath of liquid etchant which wasn’t quite strong enough to produce significant etching at room temperature. The laser (which was a visible laser, in order to pass through the etchant solution. CO2 would just be absorbed.) was focused on to the metal surface, causing localised heating and an increased etching rate.

      There was also something about laser-assisted _deposition_ of metal, but that was a little recherché ;-)

      1. Aherm, more. Part 2 of his article mentions the chromium sulphate bit. I would definitely agree with this as causing the colour (chromium sulphate is a darkish green, as are most Cr compounds), but I’d suggest that there will also be iron sulphate/oxides, as well as some of the original plaster mixed in there as well. It’s a molten mass, after all, and will be pretty well consolidated.

  4. Ha, that is a nice find! I have been doing this with Molybdenum disulfide, as that is what is in the original cermark spray. I like the theory about the chrome sulfide being the darkening agent. That could very well be, at least you bring a lot of sulfur to the melt with MoS2. If one could dilute the Moly with simple plaster and get the same effects, that would be super cool. I assume you need some moly in there to absorb the IR good enough. Moly is messy stuff though, it stains a lot.

  5. I wonder if this would work with lower power lasers like 3watt blue lasers. I have been able to etch glass by covering it in a black film before burning. Might be possible at very slow speeds.

  6. confirmed. Will let you know how this knife weathers.
    I made a paste with alcohol and plaster of paris. Painted the knife. Added some more alcohol on the knife and spread the paste out into as uniform a coating as possible. I found that undercutting with the laser left a white, but uneven etching (embossing?)… but with more power, things turn black, and stay black.https://plus.google.com/u/0/108203282175266795238/posts/UKxP8WGw1fc?pid=6100889739477936322&oid=108203282175266795238

  7. Did some tries at our fablab by getting pure calcium sulfade and IPA from the pharmacy. worked fine. Only we noticed, that compared to the cermark the results are easier to scratch of and a lot more raised (means you can very well feel more thickness).
    So I’m not sure if it’s really changing the color of the oxide alone, but build some material layer on top of the metall.

  8. Thanks for posting. I tried this and my text extended slightly past where I had put the plaster coating. The marks were just as good with nothing but bare stainless. I tried many settings working from slow and high power toward fast and lower power as well as different font sizes. It seems that in some cases the coating gave a slightly darker mark although the dark color was not always consistent and could be flaked off with a sharp blade. The real take away from me is that I could get awesome marks with no coating. I hadn’t tried it before because all I had read said it wouldn’t do anything. I also had luck marking all of my tools that I tried it on including calipers, chrome wrenches and sockets. All working as well or better without the coating.

    Laser is a 120 W Reci CO2
    Speeds are in mm/s
    Power in %
    Additional number is the scan spacing in mm. After the first couple, all were done at 0.05mm.
    The labels are speed/power
    The smallest clearest font I tried was 1mm high, Arial Narrow, with an extra 0.1 mm between letters to keep them separated. While almost every setting I tried worked, from 5/60 to 25/80 to 250/60, I decided that the 250/60 worked great while not being too hard on the tube and giving great marking speed. The finest text I tried was at 250/60 and it was perfectly legible.

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