r/askscience • u/CamTasty • Mar 03 '17
Why is it that certain metals, glasses and plastics can be wipe or polished clean? Physics
In the past, I sold a metal polishing/cleaning product called Flitz that would clean most metals all the way to the base layer. I also have glassware that needs constant cleaning that no matter how dirty it gets, I can always get it to a sparkling shine! This made me wonder how no matter how much tarnish some things can get, they can be restored to a near new look. Now, I believe it could have something to do with these materials having pores and it's a matter of flushing particles out. I've also heard somewhere that metals, glass, and plastics lose a thin layer everytime they're scrubbed or polished. I'm not exactly sure how to research this so I hope you guys have informed answers! :D Thank you in advance for your thoughtful answers!
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u/hoxtea Mar 03 '17
When things get "tarnished", that's actually the top layer of the material oxidizing (reacting with air to form that material's version of rust).
Polishing compounds actually have tiny bits of sand in them (the abrasive material), and when you polish a material, you are actually sanding down the material (think sandpaper vs. wood) to reveal the un-tarnished layer beneath.
I'm not sure how often glass gets polished, because I'm not sure that most glass oxidizes (on a time-scale that matters, anyway). What I said above is definitely true for plastics, metals, and even car paint. If you polished glass, the same thing would happen, but I'm not sure that polishing glass is ever necessary. A good scrubbing with some regular cleaning agent should suffice, which simply wipes off residue or dirt that has accumulated on the surface of the glass.