Vacuum metallization is a process for coating objects, most often engineering plastics, with an extremely thin (~0.1 μm) metallic coating. It’s done, essentially, by condensing vaporized metal fumes on the surface to be treated inside a vacuum chamber, and is a common means of “chrome plating” plastic parts used, for example, in toys.
I have been hacking on some cheap R/C cars, lately, and wanted to etch these metal films off of a few of the bits, A) to prevent it from shorting across exposed electrical connections and B) for aesthetic purposes. It looks gaudy, IMHO, and does not take paint very well. I knew that the usual strong acid and base suspects would remove it, and at first I was etching parts in disposable plastic cups containing about 12 oz of tapwater and 1/8 tsp Red Devil lye, which of course is sodium hydroxide. Hydrochloric (aka muriatic) acid will also do the trick.
I am not especially intimidated by these substances, but many people don’t keep them around, for whatever reasons. And unless you’re in a hurry, there’s no reason to use them if something milder will serve. I got curious, and did a simple test with some household chemicals. I broke a metalized “roll cage” from an R/C truck into five pieces and soaked each in a different solution overnight. I used vinegar, an arbitrary mixture of vinegar and hydrogen peroxide (the strong hair-bleaching kind), straight hydrogen peroxide, diet coke, and an arbitrary mixture of diet coke and hydrogen peroxide.
It was not a very scientific process, but vinegar seems to work well. Specifically, I used “extra strength” distilled white vinegar labelled as “9% acidity.” Hydrogen peroxide seems to have no useful effect. Diet coke works pretty well, but the carbonation causes bubbles that displace etchant and leave shiny spots on the surface. Your mileage may vary, depending on just how your parts were metalized (and with what metal), but if you have need of this process, vinegar may be a good place to start experimenting. Also, though I wanted to completely remove the metal films from my parts, it should be fairly straightforward to apply masking agents and etch decorative and/or functional patterns in them, if you should need or want to.
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.View more articles by Sean Michael Ragan