Okay, so I was trying to clean an old silver coin with a bit of aluminum foil and hot water, and I added some baking soda like I’ve seen online. It definitely did something—there was fizzing and the water got cloudy—but now the coin has these weird dull patches and a faint smell. I thought it was a straightforward redox reaction, but the result has me second-guessing what actually happened at the surface.
That fizzing must have felt like a science fair moment, but the faint smell and those dull patches make me worry you might have altered the surface more than you intended.
This is probably a redox situation where aluminum reduces the tarnish, likely silver sulfide, when you run hot water and a basic medium. The cloudy water is you dissolving or reconfiguring surface compounds. The dull patches could be areas where the surface layer was etched unevenly, exposing a different microtexture, and the smell might come from reaction byproducts or sulfide compounds hanging around. It is not just a simple wipe.
I am not convinced this always cleans coins safely. The foil trick can strip patina or even corrode the surface if the metal is not stable under alkaline heat.
Maybe the bigger question is not did redox happen but what counts as clean for a coin patina has its own meaning and over cleaning can erase history.
Take it slow now rinse with plain water let it dry and compare before and after in good light. If the surface looks different under a loupe you may have etched it.
From a craft perspective the change in sheen can read as a glaze layer or roughness which changes how light hits the relief. It is a reminder that surface physics and aesthetics walk hand in hand.
One more thought what if the fizzing was not just a cleaning reaction but a tiny sacrificial process that alters more than tarnish It makes you question how many layers a coin actually has and what a clean surface means in conservation terms.