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Chemical Woodburning

If you want to apply a maker’s mark or other repeated pyrograph to wooden goods, but can’t justify the expense of a custom branding iron, an indistinguishable effect can be achieved by applying a strong solution of ammonium chloride, for instance using a foam rubber stamp, followed by relatively mild heat.

On heating, ammonium chloride decomposes into ammonia gas and strong hydrochloric acid (NH4Cl → NH3 + HCl). Ammonia diffuses away into the atmosphere, leaving the strong acid behind, which burns the wood. The resulting chemical burn is identical to a heat burn in most respects.

This process sounds nastier than it is, in practice, and although prudence dictates erring on the side of caution and working with plenty of ventilation, the process does not produce a noticeable smell either of ammonia or of HCl. The only detectable odor is burning wood.

CAUTION: Ammonium chloride fumes can cause respiratory harm or an asthma-like allergy, so avoid breathing dust, vapor, mist, or gas. Wash thoroughly after handling. Store ammonium chloride capped at room temperature and protect it from heat.

Preview

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Steps

Step #1: Prepare stamp

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  • For my simple "MAKE" stamp, I used these plastic-backed 1.5" foam-rubber letters from a hobby store.
  • Apply a strip of carpet tape to a suitably-sized piece of MDF, plywood, or other flat back. Remove the tape backing.
  • Arrange the letters as needed and push down the backing around each to fix it in place.

Step #2: Measure and add solid

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  • Although the photo shows me working with bare hands, you should err on the side of caution and wear latex or nitrile gloves, as well as goggles, from this point onward in the project.
  • Take a piece of paper and fold it in half lengthwise.
  • Lay it out on your work surface, then measure 5 level tablespoons of ammonium chloride onto the fold.
  • Gather up the paper from the long edges and form a channel, pouring as shown, using the fold to direct the solid into the mouth of the bottle.
  • If you want more or less than 500 mL of "ink," the formula is 1 tablespoon ammonium chloride per 100 mL water.

Step #3: Add water and mix

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  • Pour 500 mL of warm water into the bottle on top of the solid ammonium chloride. Tap water should be fine.
  • Put the sprayer, or a matching cap, on the bottle and tighten it down securely. Shake the bottle gently until all the ammonium chloride is dissolved.
  • CAUTION: Although these photos show me working with bare hands, use caution and wear latex or nitrile gloves, as well as goggles.
  • NOTE: If you want more or less than 500mL of “ink,” the formula is 1 tablespoon ammonium chloride per 100mL water.

Step #4: Prepare stamp pad

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  • Set out a flat, shallow, aluminum or plastic tray that's big enough to accept your stamp.
  • Line the tray with felt.
  • Saturate the felt by misting it generously with ammonium chloride "ink" from the spray bottle.

Step #5: Ink and apply stamp

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  • You'll want to practice this process a couple times on scrap wood before trying it on anything important.
  • Put the stamp onto the felt and press down with some force to "ink" it.
  • Transfer the stamp to the workpiece, line it up carefully, and press down with about the same force to transfer the ink.
  • CAUTION: If you let the “ink” sit on a wooden surface too long, it may diffuse along the grain and blur the image.

Step #6: Apply heat

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  • If you let the "ink" sit on a wooden surface too long, it may diffuse along the grain and blur the image.
  • Immediately after applying the stamp, pick up the heat gun and begin applying heat. I used the "high" setting on my heat gun.
  • Play the heat gun evenly across the surface of the work. Within a minute or two the inked areas will begin to turn yellow, then brown, then brownish-black.
  • You're done! For all practical purposes, the resulting chemical burn is indistinguishable from a heat burn. It is waterproof and can be finished or otherwise treated like a conventional pyrograph.

Step #7: Going Further

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  • The “ink” described here is nothing more than an 80% saturated solution of ammonium chloride. Though it works well enough, there’s plenty of room for improvement. Adding egg whites or other thickener, for instance, might improve the handling qualities by reducing the tendency of the ink to diffuse along grain lines.
  • And there’s no reason it has to be applied with a stamp. You might just as well use a stencil, marker, brush, inkjet printer, or some other means.
  • Other surfaces should also be susceptible to this treatment. It will certainly work on paper and cardboard. Leather, too, perhaps? Metal? Let us know what you find out at makezine.com/projects/chemical-woodburning.
Sean Michael Ragan

Sean Michael Ragan

I am descended from 5,000 generations of tool-using primates. Also, I went to college and stuff. I am a long-time contributor to MAKE magazine and makezine.com. My work has also appeared in ReadyMade, c't – Magazin für Computertechnik, and The Wall Street Journal.


  • http://worshopshedtest.wordpress.com Workshopshed

    I’m wondering if this would work with stencils too?

    • 9938ddd

      “And there’s no reason it has to be applied with a stamp. You might just as well use a stencil, marker, brush, inkjet printer, or some other means.”

  • Malcolm

    OK, so you might think this is easy!! I’ve just paid out for a 1Kg tub of chemical, made up the solution, stamped it on some wood, heated it up and got a white imprint of the stamp which washes off. NO burn whatsoever!! Can you tell me where I’ve gone wrong or tell me what to do with the remaining pot of chemical I have left?

  • Malcolm

    I’m just using a hair drier on hot setting and fan on slow speed. And thanks for the speedy reply – much appreciated as I’m getting hassle from the boss!!

  • padson

    …tried that too!

    -did not work with a hair dryer, but worked with a gas-burner!
    -when applied high concentrations I got the white as well, its just the crystallised salt and will burn with higher temperature!

    yeah!!

  • Lyle

    I’m really interested in trying this. My plan is to use my 3D printer to create stencils and spray the solution using a squirt bottle. Can anyone comment on the reaction (safety, fumes, etc.) between PLA (my preferred filament), ABS and the acid?

    Awesome write up Sean!

  • Nitrous

    Might be a silly question, but why not just use muriatic acid? It’s readily available and easy to handle. As an aside, do you neutralize the surface after heating?

    You likely know this, but ammonia vapour (say from ammonia water sold in stores as a cleaner) will combine with HCl vapour to form ammonium chloride. I it will appear as a nice white smoke-like material in the air.

    Nice tutorial.
    Thanks

  • Andre Binette

    Sounds like just what I need to sign my dried gourd art. Where can I purchase the amount of Amonium Chloride mentioned for this and is it expensive?

  • http://twitter.com/ryandrake Ryan Drake (@ryandrake)

    The hardest part of this to find is the foam letters. The only ones I can find that do not have magnets or stickers on them are only about an 1/8th” thick.

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  • Francois Madore

    and does it burn the foam rubber after a while?

    is it ok to use directly hydrochloric acid instead of sal ammonia? (as i can find it more easily)

  • Anna

    Have you tried it with the egg added? I’d like to be able to paint a more complicated design. I think I would also add a touch of dye so I can see where I’m painting. And then I guess I would heat it piece by piece?

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  • Dave Miller

    I cut a vinyl decal on a vinyl cutter. Applied it to wood. Painted with
    matte clear coat. Rustoleum 2X spray paint. Removed decal. Let dry.
    Apply the ammonium chloride solution. Heat gun as usual. Done. End
    result, is perfect. NO bleeding, or discoloration. Just a perfect
    result. I did this on some junk old pallets that were made of pine and
    it worked. Hydrochloric acid will only burn the organic wood and leave
    the painted “inorganic” surface untouched. You’re welcome.