It's easy and safe — use a 9V battery, vinegar, and salt to permanently etch markings on metal.
As a homebrewer I often need to measure my kettle volumes at various stages during the brew day — to figure out my brewing efficiency, or monitor evaporation rates, or compare boil volumes to what my recipe estimated. Unfortunately, a lot of brew kettle manufacturers don’t put volume markers on their wares.
Some brewers install an expensive sight glass into their brew kettle to monitor volumes. Some brewers dip a homemade measuring stick into the wort. I used to use a measuring stick, but I got sick of relying on an extra tool during brew day, and I didn’t like the added risk of contamination from dipping the stick into my cooled wort. I wanted a permanent solution built right into the kettle that would always be reliable.
While researching metal etching, I came across a technique commonly used by knife makers to leave their brand on their knives. This technique involves electrolytic acid etching. It sounds complicated, but I’ve adapted it to require nothing but cheap household materials.
The basics of the process are very simple. It etches a mark on the surface of the metal by passing a very low-voltage current through the metal in the presence of acid.
In this technique, you’ll use vinegar for the acid. To facilitate this process, the vinegar must be conductive, so you’ll simply add an electrolyte, in this case, salt.
The power source should be around 9 to 12 volts DC, to leave a frosty white mark that’s permanent. I recommend a 9V battery.
To apply the acid and the current, you’ll construct an etching tool out of a Q-tip. The cotton head of the swab will hold the vinegar solution, and the wire will receive the current from the vinegar-soaked cotton.
This method is not limited to kettles or volume markings. You could add a logo to nearly any piece of metal equipment (in either aluminum or stainless steel). Imagine your custom logo all over your homebrewery!
Here’s the science behind it: In the vinegar, the salt dissolves into positively charged sodium ions and negatively charged chloride ions. This allows current to travel through the solution. In the presence of acid (vinegar), the electrical current causes the ions in the metal to dissolve so they can travel in the direction of the current, which, in this case, is away from the metal. This permanently removes metal from the surface, which changes its texture. The different texture reflects light differently — making the markings permanently visible. The reaction also produces carbon dioxide, which causes the fizzing. This is the opposite process to electroplating, which would be the result of reversing the polarity.
What about corrosion risks? Stainless steel and aluminum both naturally form oxidized coatings on their surfaces when exposed to oxygen. This oxidized layer is what protects them from rust and corrosion. A few seconds after etching, the surface of the etched area will oxidize again and will be the same as the rest of the brew kettle, thereby protecting it. Still, before etching your expensive brew kettle, I strongly recommend testing this process on another piece of metal that you don’t care as much about, or a very inconspicuous area of your kettle such as the inside of the lid. You don’t want any surprises.
CAUTION: Some stainless steel alloys include chromium and may produce trace amounts of hexavalent chromium , a known carcinogen, when electro-etched. Wear disposable gloves when etching, and rinse the etched metal object thoroughly under running water before using it.