Fetching Etchings for Stainless Steel

What do you do when you have a 10-gallon brew kettle (or any other stainless steel or aluminium thing) with no volume markings (or Hack a Day logos)? If you’re [Itsgus], you use science to etch some markings with a few household items and a 9V and you call it a day.

[Itsgus] used 1/4c vinegar and 1/4tsp of salt to form an electro-etchant and applied it with a Q-tip connected to the negative terminal of a 9V. He used tape to connect a wire between the positive terminal and the kettle. The vinegar dissolves the salt, creating negatively charged ions. Connected correctly to a 9V, the process removes metal where the current flows. If you were to connect it in reverse,  you would add a small amount of metal.

The process only takes a few seconds. When the etchant starts to sizzle and bubble, Bob’s your uncle. Even though the stainless steel’s natural coat re-oxidizes over the etches, you should probably wash that thing before you brew. If you prefer adding metal to removing it, try electroplating copper on the cheap.

24 thoughts on “Fetching Etchings for Stainless Steel

    1. While I’m not a metallurgy expert, stainless steel is homogenous (ie. no coating). (Of course strictly this is wrong, cause steel.).
      I’ve got a pair of stainless steel tweezers that sat in NaOH and their ends got matte, probably because of touching aluminium in solution. They don’t rust.

      1. Yes, it’s homogeneous and won’t corrode _on its own_. IIRC, the chromium also forms a protective oxide layer on the surface.

        However, if the metal is in contact with a different metal (e.g. a screw), even a different variety of stainless, then it can corrode if there’s an electrolyte present. I have some gate latches outside that I made from stainless steel parts brazed together, and there are small spots of rust near the brazed joint.

        1. I think the small rust spots are more likely from change in composition due to heating. I noticed this as well with a stainless brew kettle which I had welded a stainless fitting into, though it’s also possible with dissimilar metals. I believe there’s an old mil-spec table on the net somewhere that describes the properties of dissimilar metal compositions.

          1. Google would probably turn up that table or one like it with the key words “galvanic corrosion”. What I find most interesting is that you can also use the galvanic properties of dissimilar metals to *prevent* corrosion… see “sacrificial anode”.

        2. It’s been a while since I read on the topic, but if I’m remembering it correctly the chromium ions move to the surface and prevent corrosion. So if you get a gouge (or etch) over time the chromium ions deeper in the metal will move outwards and restore the corrosion resistant surface. This isn’t perfect, though, and you can still get some corrosion if the environment is particularly bad or the damage is large.

      2. It still rusts, it just rusts less; ie. stain-less steel. The chromium forms a protective oxide layer protecting the iron. The chromium is homogeneous* throughout the steel, it does not migrate. So unless you have exceptionally crappy steel the rust is not due to lack of chromium. Most stainless steel in food utensils is 304 or 316. You can look up spec sheets for them if you’re truly curious about the trace metals used.

        Fittings may be a different alloy due to ease of machining. Filler rod also plays a role. Because as was mentioned any time you join dissimilar metals physically or electrolytically you are creating a voltage potential; a battery.

        *homogeneous in the sense that Cr, and other trace elements are evenly distributed throughout the material. Certain heat treatments can change the position of trace elements in the overall crystal structure but this has little effect on the chemical behavior of the material.

      1. Timo is correct, sort of. No metal would actually deposit, because there are no free ions floating around. If your swab solution contained metal ions, they would deposit until depleted.

        1. but you’ve put copper in an acid solution, sure vinegar is a weak(chemically) acid but with a few tens of mA behind it shouldn’t some amount of Cu get mobilized? I’m too lazy to break out my electrochemistry text.

    1. It’s also probably one of the less exciting Xp. Usually I read a hack and my mind wanders to all kinds of unfeasible places.

      This hack however is probably the one I’m most likely to ever use.

  1. Yummmm—– Hexavalent Chromium!

    Seriously though, the amounts of toxic metal ions released by this process would be small for this tiny job, I think the EPA regulations in the US generally outlaw this process to be performed in a home environment without a license and process controls like they do with freon release etc??

  2. Wow this is amazing, considering you could get the supplies from the dollar store, and if you wanted to add metal you could charge the q-tip in a solution with a, say, gold coin, reverse the polarity and deposit the gold ions on the pot, this could have some interesting potential.

  3. I seen this on brewing forums, and a point has been discussed in the comments in that the etched surface will rust unless threated.

    The go-to treatment for this is soaking the etched surface in citric acid and heated for a time. The less pure the citric acid source the hotter and longer you need to treat it for.

  4. Hmmm… Could this method be applied also on sterling silver? That would solve my problem of acquiring the chemicals.

  5. Once Again, HackADay is being a Reddit Repost engine. Once in a while is fine, but the frequency is starting to be ridiculous, again.

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