Greetings fellow nerds.
In this video we're going to restore tarnished silver using electrochemistry.
First i need to issue a warning to any silver collectors, coin collectors or antiques dealers.
Artificial chemical alteration of silver is very poorly received by the collector community in general.
Do not perform this on any pieces that have any historical,
numismatic or other value beyond the spot price of the silver metal itself.
Our objective in this video is to explore the science.
Anyway I made s silver restoration video back in 2009.
I personally really liked it and have always wanted to redo it
but using a modern 4k resolution camera as opposed to the really low end 720p camera i had back then.
So let's get started restoring silver by electrochemistry in 2017.
So first we need to make our restoration solution.
We start with 200mL of water and add to it 20g of table salt and 10g of baking soda.
Stir for about 5 minutes.
It won't all dissolve but that's acceptable.
It also helps to heat up the solution so it works faster during the restoration step.
Now get a shallow tray with some aluminum foil and pour in our restoration solution to cover it.
This actually works best with an all aluminum tray but i'm using foil so i can show you the chemistry.
Let me zoom in for a better look.
And here is our badly tarnished silver coin.
Technically it's a silver round but the chemistry is the same.
Now putting it into the solution by itself nothing will happen.
We need an electrical connection for this to work.
So let me put it on top of the aluminum foil to connect them.
And there we go.
I'm not timelapsing this.
This is really happening that fast.
And that is our restored silver coin.
Let me do it again this time with a deeply tarnished silver coin.
This will take a lot longer but it will still work.
So what's happening? The colored tarnish on the silver is actually silver sulfide
formed by reaction with small amounts of hydrogen sulfide and oxygen in the air.
In the solution we set up a basic electrochemical cell.
The aluminum foil is the anode and is oxidized in the alkaline solution releasing electrons.
Normally these just go to making hydrogen gas but if we touch the silver to it then the electrons go into the silver.
The silver behaves as the cathode and reduction occurs.
The silver sulfide is converted back into silver metal and the sulfide ions go into solution.
Overall we're transferring the sulfide from the silver to the aluminum.
Now this works so well with aluminum because it has a much lower reduction potential than silver sulfide.
So it's strong enough to force the back reaction of converting silver sulfide back into silver metal.
So you might be asking what would happen if we tried a metal other than aluminum.
Let me try again this time using nickel metal.
Nickel has a much higher reduction potential than aluminum.
In fact it's even higher than silver sulfide so as you can see nothing happens.
The oxidation of nickel just isn't strong enough to force the reduction of silver sulfide.
Let me try it again now this time using a strip of nickel in which we've plated zinc metal.
The upper end of the stripe is still nickel metal.
Now zinc has a lower reduction potential than silver sulfide so this should work.
But to make this experiment more interesting i'm going to put the tarnished silver on the nickel end.
Interestingly enough it's still working.
This emphasizes the electrical nature of this experiment.
The zinc is being oxidized by the solution as usual but the electrons travel through the nickel strip
and into the silver where the reaction takes place.
The nickel itself doesn't do anything but is the conductor for the electrons.
Now let's take this a step further.
If this is all about pushing electrons, then we should be able to force the reaction forward with a battery.
A battery provides its own power and can push reactions that aren't favorable on either electrode.
So here i am zoomed in onto a heavily tarnished coin and i'm attaching the negative terminal of the battery to it.
Now all we need to do is touch the positive terminal to the solution and complete the circuit.
The battery will rip electrons out of the copper wire and force them into the silver.
This should be much faster since we're using a six volt battery pack.
Far greater voltage than the lowly 1.6 volts of the aluminum.
Ready.
3..2..1..
That was over in less than 2 seconds.
Let's see that again.
Interestingly enough the reduction wave starts nearest the positive wire, the anode, and moves away.
Even if we do it on the same side the effect is dependent on the anode wire position.
This is because the silver sulfide closest to the anode is the most strongly polarized and is reduced first.
Once that's reduced the electrons go to the next most easily reduced silver sulfide
which is slightly less polarized a little further away.
This effect repeats and gives us this wave.
So that was the restoration of silver using electrochemistry.
I hope you enjoyed my video.
And let me know if you think i should redo any other old video in modern high quality.
Special thank you to all of my supporters on patreon for making these science videos possible
with their donations and their direction.
If you are not currently a patron, but like to support the continued production of science videos like this one,
then check out my patreon page here or in the video description.
I really appreciate any and all support.