I have my late grandpa’s silver spoon attached to my fridge with a neodymium magnet. What kind of chemical reaction causes that discolouration?
I have my late grandpa’s silver spoon attached to my fridge with a neodymium magnet. What kind of chemical reaction causes that discolouration?
Generally it’s silver reacting with (trace) amounts of sulfur containing gasses in the air to form silver sulfide.
Silver sulfide isn’t blue, but the colours, and especially the multiple hues are caused by thin-film interference. That’s the same effect that gives soap bubbles that shifting multi-colour effects.
The only way to remove it, is by grinding off a tiny bit of material, which is what you do when you polish it. The tarnish doesn’t go further than the surface layer, so it’s actually a pretty amazing way to preserve the metal.
Fun fact: if you ever want to make silver look old, put it in a closed box or bag with a hard boiled (or rotten, but I suggest boiled) egg. Those are high in sulfur compounds and will add months of tarnish in minutes.
I’d use a pencil eraser to polish off surface level tarnish, no need to bust out the grinders here. But otherwise your comment is on point.
He’s not saying use a grinder. He’s describing polishing as micro-grinding.