Every Dark Spoon has a Silver Lining – Using Chemistry on Silver Tarnish
by: Ted Beyer
The holidays have just passed, and for most people, part of the celebration involves getting out the “good” china and flatware to set a festive table. Like most people, I have a few pieces of silver and silver plate that don’t get a lot of use, but are nice to use on special occasions. Thing is, over time, silver tarnishes – it turns dark, and if allowed to continue long enough, it turns black. So out comes the polish and you get to spend all kinds of time polishing it. And with silver plated items, if you do that often enough, eventually, you will polish the silver completely off!
But wait – science will come to the rescue!
The tarnish is actually the result of a chemical reaction between the silver and sulfur-containing substances in the air. The silver is actually combining with sulfur and forming silver sulfide. Silver sulfide is black. When a thin coating of silver sulfide forms on the surface of silver, it darkens the silver. That’s what we call ‘tarnish.’
There are two ways to remove the offending silver sulfide. One way is to strip it from the surface. The other is to reverse the chemical reaction and turn silver sulfide back into silver. Polishes that contain an abrasive shine the silver by rubbing off the silver sulfide and some of the silver along with it. Another kind of tarnish remover dissolves the silver sulfide in a liquid. These polishes are used by dipping the silver into the liquid, or by rubbing the liquid on with a cloth and washing it off. These polishes also remove some of the silver.
Obviously, the better way to do away with the tarnish is to reverse the reaction that created it in the first place, and save your silver! This is something that is easy to do at home with commonly found items. It’s a nifty technique for silver or silver-plated objects, but probably not something you’d want to attempt on your most valuable or antique silver pieces.
You will need:
- Your tarnished piece of silver
- A container large enough to completely immerse the silver in (think roasting pan…)
- Aluminum foil to cover the bottom and sides of the pan
- Tap water (enough to fill your pan so you can completely immerse your silver)
- A pot to heat the water
- Pot holders – you will need these to handle the pot of hot water
- Baking soda (about 1 cup per gallon of water)
Line the bottom of the pan with aluminum foil. Place the silver object on top of the aluminum foil. Make sure the silver touches the aluminum. Place the pan in an empty sink.
Heat the water to a full rolling boil. Remove it from the heat – the next step will make the water froth a bit and it may spill over, so be careful! Add about one cup of baking soda for each gallon of water. (If you need only half a gallon of water, use half a cup of baking soda, etc.). As I mentioned, this will cause the water to froth quite a bit and it may boil over the top of the pot. That’s ok. Immediately pour the hot baking soda/water mixture into the pan, and so that it completely covers the silver. Almost immediately, the tarnish will begin to disappear. If the silver is only lightly tarnished, all of the tarnish will disappear within several minutes – or even seconds! If the silver is badly tarnished, you may need to reheat the baking soda and water mixture, and give the silver several treatments to remove all of the tarnish.
You will notice that often the water will look slightly yellowish and dirty and smell faintly of rotten eggs. That is the sulfur that has been detached from the silver. I found that when using this process, trying to re-use the solution more than twice really slowed the reaction down. Since baking soda is cheap, I just make up a new batch of water and baking soda every two or three treatments.
You will also notice that the silver will dry with a bit of a white residue on it. That is just residual baking soda – a quick rinse in clean water and a dry with a towel will make that disappear, leaving you with nice bright silver.
And now for the real science:
As previously mentioned, this tarnish-removal method uses a chemical reaction to convert the silver sulfide back into silver. Many metals in addition to silver form compounds with sulfur. Some of them have a greater affinity for sulfur than silver does. Aluminum is one of them – and luckily, most people already have lots of it in a convenient to use form in their kitchens. In this case, the silver sulfide reacts with aluminum. In the reaction, sulfur atoms are transferred from the silver to the aluminum, freeing the silver metal and forming aluminum sulfide. Chemists represent this reaction with a chemical equation.
The reaction between silver sulfide and aluminum takes place when the two are in contact while they are immersed in a baking soda solution. As with almost all chemical reactions, the reaction is faster when the solution is warm. The solution carries the sulfur from the silver to the aluminum. The aluminum sulfide may adhere to the aluminum foil, it may be found floating in the water having detached from the foil or it may form tiny, pale yellow flakes in the bottom of the pan.
The silver and aluminum must be in contact with each other, because a small electric current flows between them during the reaction. This type of reaction, which involves an electric current, is called an electrochemical reaction. Reactions of this type are used in batteries to produce electricity. Hopefully, this little bit of science will make your future holiday preparations faster and easier – not to mention saving your silver to be enjoyed for many years to come.
I have been told that using ‘washing soda’ (Na2CO3) is more efficient/less time consuming and perhaps easier on the silver piece than Sodium Bicarb. Are these statements correct?
Thanks for asking. We sent this question out to Ron Perkins, the founder of EI and retired Chemistry of over 30 years and this is his answer.
Most of the methods published use aluminum and hot water containing baking soda in order to make a slightly basic solution. A few recipes suggest substituting baking soda with washing soda which would give a stronger basic solution and cause the reaction to occur faster, but this substitution is definitely not recommended for valuable silver pieces.
Although this electrochemical process will indeed remove the tarnish and make the silver appear shiny again, the process should not be used on valuable silver pieces such as coins, antique silver, or sterling. The problem is that the process returns the silver from the tarnish to the surface of the metal object but probably, not where the silver atoms were originally. Under a microscope, the originally smooth silver surface can be seen becoming more pitted and rougher each time the tarnish removal process is used.
I hope this helps. Please let us know if you have any other questions.
Loved this article. Thank you so much for posting it – I love having the explanation as well as the technique.
Will this work on copper/brass? From what I’m reading, the darkening/verdigris on copper is more likely to be copper sulfide than copper oxide, which made me wonder whether the sulfur could be reclaimed from that, too. Do you know?
In order to find the answer to your question, we reached out to Ron Perkins, the founder of Educational Innovations and Chemistry teacher for over 30 years. This is what he said:
If the tarnish is a sulfide of copper, the same method may work to obtain pure copper. I’ve never thought of trying it nor have I read anything about it. Sounds like a good experiment for some student to try.
Sooooo, having a little trouble with an unclear antecedent. When you suggest that we not use “this” treatment on antique silver, you mean the entire concept of the electrochemical reversal of the tarnishing? or just the washing soda version? I have used washing soda for tarnish removal decades ago, but was not happy with the result, probably for the reason you give. The texture was never as silky and lovely ever again. I now deal in fine antique silver and just yesterday could feel the temptation to start boiling when a particularly intricate teapot was giving me fits. I suspect you meant either medium would be damaging.
This from our founder (and chemistry expert), Ron Perkins:
The problem is that although the chemical reaction with Al, and baking soda removes the sulfide from the silver sulfide, the remaining silver doesn’t end up in its original place on the object, making the object no longer shiny and smooth.
You can find some of the best silver cleaning advice is in this article:
One rule: never clean antique coins !!!! Sell them “as is” and let the buyer decide what to do.
Hope that helps!
what is the specific problems of silver sulfides
It says that the aluminum must make cpontact with the silver for the electro-whatever to take place. Will it work if siverware is piled loosely in the container? the pieces are touching each other and several contacts are made directly to the AL foil. I get that with using more pieces the process might be less effective.
I used the baking soda solution and aluminum to clean some sterling silver that had been sitting in the back of a cupboard for decades and was totally black. I put it on low heat on my stove to keep it warm. Left it too long, and now there is a rough whitish coating on some of the pieces. What is this and can I do anything about it?
Im wondering if silver gets tarnidhed and is left in that state, will the tarnish “eat away” at the silver over time, thoroughly corroding it, such as rust does to iron?
No, the silver “tarnish” covers the surface and protects the underlying silver from reacting with the sulfur products in the air. The tarnish basically forms a protective, yet, ugly layer on the silver metal.
Thank you so much for your cool post. We homeschool and I love thrifting, so for an outing we specifically searched for silver items at the Goodwill in our neighborhood. We found some amazing candle sticks and your pots totally cleaned them, restored brilliantly!
Would the reaction be expedited by insulating the silver target from the aluminum and applying a voltage between the two? (positive to aluminum, negative to silver)
In electrochemical reactions, one always needs a complete circuit, otherwise nothing happens. If the Ag is insulated from the Al it is not a complete circuit.
This would be like attaching an Al wire to the positive terminal and a silver wire to the negative terminal of a battery and not letting the wires touch. — one would not expect anything to happen. There can be no flow of electrons.
Electrochemistry is fun to think about and relatively safe to see what happens if you use only a single flashlight battery, a D or C cell.
Have fun experimenting.
I tried the experitment – DC powere supply, + to aluminum, – to silver, sodium carbonate (baking soda) solution. It works!. Rapid evolution of H2S where previously was getting nowhere with just hot solution. Current starts to flow at about 2.7 Volts.
I tried the experiment – DC power supply, + to aluminum, – to silver, sodium carbonate (baking soda) solution. It works!. Rapid evolution of H2S where previously was getting nowhere with just hot solution. Current starts to flow at about 2.7 Volts. Silver cleans up nicely but needed a minor final once over with silver cleaner.
could i bother you to give me more information on this experiment you did?
id really appreciate it, thanks!
Thanks for sharing your experiments!
Reading through it I saw that the reaction is partially incorrect. The product of the reaction is aluminium oxide, Al2O3 and not aluminium sulfide, Al2S3. The latter is actually unstable in aqueous medium, decomposing to Al2O3. See overall reaction below:
OXIDATION: 2 Al(s) + 6 OH– (aq) –––> Al2O3(s) + 3 H2O (l) + 6 e–
REDUCTION: Ag2S(s) + 2 H2O (l) + 2 e– –––> 2 Ag(s) + H2S (aq) + 2 OH– (aq)
Overall reaction: 3 Ag2S(s) + 2 Al(s) + 3 H2O (l) –––> 6 Ag(s) + 3 H2S (aq) + Al2O3(s)
Thanks so much, Priscilla! We always appreciate input! For those reading, Priscilla correctly noted that Al2S3 in water decomposes spontaneously into H2S and Al2O3. For those taking advanced or college chemistry, Priscilla even provided the two Half-Reactions:
OXIDATION: 2 Al(s) + 6 OH– (aq) –––> Al2O3(s) + 3 H2O (l) + 6 e–
REDUCTION: Ag2S(s) + 2 H2O (l) + 2 e– –––> 2 Ag(s) + H2S (aq) + 2 OH– (aq)
Overall reaction: 3 Ag2S(s) + 2 Al(s) + 3 H2O (l) –––> 6 Ag(s) + 3 H2S (aq) + Al2O3(s)
Please can you tell what is the role of aluminium foil in this activity.
The aluminum gets oxidized, so the silver can get reduced.
That is, some aluminum loses electrons and becomes Al3+ ions, while the silver ions that have combined with sulfide ions to make tarnish gains the electrons and goes back to neutral silver metal.
I have a ring that I would like to do this for. The ring has a sapphire stone in it. Will the sapphire react with the baking soda, aluminum, or hot water?
Thank you 🙂
To be perfectly honest with you, that’s a much better question for a jeweler than for us. I wouldn’t think so, but I wouldn’t take a chance without asking a professional jeweler.
Color gem stones often get their color from the presence of “contaminants” which are usually AL-based. This is usually called, “corundum.”
Sapphires are no exception.
So I would expect any such gemstone to become “clouded” on exposure to base solutions.
Such clouding would probably stay on the “surface” of the stone, but the remedy for it will probably be more expensive and time-consuming than simply rubbing the silver piece with a polishing compound, or dipping it in a jewelry cleaner.
Hello thank you for your the information but why did the experiment use hot water? Do you think tarnish removal would be faster or slower in the water at room temperature? Also, what are your recommendations for improving the speed of tarnish removal in this process?
From the author, Ted Beyer:
The rate of reaction is vastly increased by the use of hot water (many reactions occur more rapidly at higher temps). The same reaction will occur at lower temperatures, but will take far far longer. I know — I tried using the water solution more than once without re-heating it…
To my knowledge, there is no way to improve the speed of tarnish removal. Experimentation on my part caused the tarnish to disappear virtually instantly when using boiling water and the method indicated — and instantly is about as fast as any reaction can go… If proper contact between the silver and the aluminum is not maintained, the reaction, regardless of water temperature, will not occur, and for some irregularly shaped objects that can be a bit of a challenge.
Hi Can you tell me when the chemical process “silver black” was created? I’m finding a lot of Native American jewelry is being chemically processed to make it look vintage when it’s really new. Just wondered how long ago this process came into being. It will help me date pieces.
25 years ago, I bought silver oxidation preventer papers for our Moms for Christmas. They were long, maybe 1.5 inches wide, light blue gray. They put them inside their selves drawers, inside their displays of silver tea services, punch bowls and other things that were out all the time. Now I can’t find anybody who ever heard of them! Anyone tell me where I can find some of these.? I think they came in ziplock type bags of 10 or twenty with writing on each slip of paper.
What a great idea! I just found 3M Anti-Tarnish Carbon Paper strips on Amazon. I’m going to buy some and try them. Anyone want to explain the chemistry? Thanks!
When I aquired my great aunts jewelry collection and jewelry boxes, she had wrapped some pieces in paper towel type material and included a piece of chalk .. also just had pieces of chalk laying in various sections in all of her jewelry boxes. all jewelry showed no signs of oxidation, rust, any damage at all or tarnish so I’ve just continued using chalk in jewelry boxes. Seems to work. can’t recall if there was any silver 925 or gold but all other metals used in making the old, antique “costume ” jewelry stays quite nice just with white chalk in the boxes or bags used to store it in.
does this process eats up silver from the utensil? if yes, can that be extracted back from the residual water and almunium foil and how?
Will appreciate your quick reply.
It does not eat up the silver. The sulfur is removed from the silver-sulfide (tarnish), leaving the silver behind.
I’ve read your article and the comments and answers. I’m a little confused about the chemical reaction with baking soda. In the original you said it brings the shine back to the silver but in a response you said it’s dull because the silver atoms are not all returned to where they belong. So which is it? Is this advised or not?
I have some silver and turquoise jewelry. Would I be able to submerge those pieces in the solution? If not, how would you suggest cleaning it. Thank you so much.
A big thank you and a big shout out to Ron. I’ve just cleaned a silver necklace that I can’t clean by any other method than this because of the shape of the necklace that has waves in it that can be straightened when there’s any tension put in it. When I finished, I looked online to find the chemical reaction so I could show it to my grandson. To my delight, I found this excellent and informative explanation, but even more exciting is the fact that it’s on your website. To understand how excited I am, you need a little history. Back in the late1980s, I started working with young children as a science educator when the nuns in my childrens’ school asked me, a stay at home mom who was taking a break from being a biochemist, if I would teach science to the children in the school. That was new area for me, but I accepted the challenge, and discovered a new calling.
A few years later, I received a catalogue that was full of the most amazing, fun science “toys” I’d ever seen. I probably bought, and still have, everything in the original catalogue. On a trip back east from California, i even visited your original location where i first met Ron whom I would later see at science conventions. Thousands of children, including my own grandsons have benefited from the company that Ron started many years ago. I’m sort of retired now, so I haven’t had the need to purchase any more materials from you, but I do always recommend your websites when the occasion arises.
That’s why I was so excited to see that Educational Innovations, a company I have loved since your very beginning, is still able to help me out when I need it .
So say hi to Ron (who used to call me his best customer), and thank you for an excellent explanation of the process i use often.
I forwarded your comment to Ron, and he was pleased to hear from you and wishes you all the best!
A very very big thank you
I have a number of coins sent from Haifa Israel that may have exposed to alkaline aerosols. See https://link.springer.com/article/10.1007/BF00479411
These silver proof coins have varying degrees of what appears to be a white corrosion layer chemically bonded with the surface, so that the surface is still mirrored and reflective. However, the white corrosion does not photograph well at most angles.
Could the corrosion be silver carbonate?
Any other suggestions?
Our recommendation would be to bring your coins to a professional. A local jeweler would probably have valuable information that will help you clean your coins without losing any of the silver. Please let us know how it turns out.
I want to do an experiment like this for my IB HL Chemistry IA, which is just an experiment, although I need something to measure in the process. I’m thinking maybe the temperature of the water but I’m not sure how I would measure the tarnish on the silver before or after the reactions. Does anyone have a recommended on how I could do a formal experiment out of this?
One idea is to carefully weigh the silver item before-hand, go through the process, carefully rinse and dry, and weigh again. The piece should lose mass. The exact mass lost will depend on the amount of sulfide tarnish present. Repeating the experiment on untarnished silver as a control to show that process isn’t removing metallic silver would go along nicely with this.
My silver rings tarnished when i touched sulfur containing hair oil. I cant wait to try out the solution. Thank you
How many moles of iron(III) oxide are needed to form 3.603103 mol of iron?
I accidentally dropped a few sterling silver rings down the bathroom sink. When I got them out about 24 hours later the one which had fallen in first, had this beautiful tarnish color to it of a deep blue and a copper color. I was wondering how I could replicate this chemical reaction without dropping the ring down the sink again.
Thanks so much and happy new year
Hi! i was just wondering if the concentration of the sodium bicarbonate would affect the rate of reaction in this experiment
The “overall reaction” equation published above by Priscila in May 2017 was just what I was looking for. However, the baking soda (NaHCO3) does not appear anywhere in the equation. Yet it is critically necessary for the reaction. So there must be more to the equation. What happens to the NaHCO3?
Bicarbonate (HCO3-) and carbonate (CO3–) produce more OH- in solution by taking a proton (H+) from water. Priscilla’s equations use OH-.
What would happen if you used a tin can lined with aluminum foil as your vessel in this process and the solution came in contact with the can?
I found the following reaction for silver tarnish:
2Ag + H2S –> Ag2S + H2
But in the reactivity series silver is less reactive than hydrogen. So how is this taking place at all?
I asked a few people and some said that the reaction also involves O2 and H2O. So, if this is tried in a setup where a silver article is placed entirely in H2S chamber and nothing else, will there be no reaction?
I am a hobby jeweller.
I can explain the white surface some posters have seen on chemically cleaned silver. This is actually silver! Dried on baking soda is also white but will rinse off. Any white left after that is pure silver which is now microscopically rough. It will return to a normal shine if polished or burnished which flattens and smooths the roughness back down.
I was cleaning some very old plated candelabra. I dont use the abrasive cleaners, and tried some dipping cleaner my mother gave me. As I was trying to get come residual wax off (after the dip cleaning) the Silver got a pinkish haze…. HELP what is it and how do i get it off???
I tried it with some old silverware. Immediately the spoons became white and after half-hour all was fine. Perfect!
I have some more silverware, one a 50-year old finely engraved box that turned completely black over the years. Tried to repeat the above with zero results, even put it on a burner at low heat to keep the liquid hot. Does not work. What could have gone wrong?
Can any one hounorable,
Please explain the,instant SILVER DIP Solutions,which are readily available in market, are made of what chemicals,
I want to make it myself,thanks
I’d like to try this with some silverware and a few pieces of jewelry, but my son (a chem major) is concerned about me breathing the hydrogen sulfide that would be produced. How much of a concern is this? He thinks this is something best accomplished under a lab fume hood. I will need equations and estimated hydrogen sulfide quantities that would be produced.
I’ve used the baking soda + aluminum foil + hot water to clean silver for years. I just read about cleaning oven racks with aluminum foil and usually detergent. Sometimes the advice is to scrub with the aluminum foil. I’m curious: What chemical reaction would aluminum foil have with racks (usually chrome(?)) or the grime (unknowable composition)? Any thoughts?
I have an old cloisonné vase with silver wire to form a design which was filled with enamel to color the design. The vase has spent its life in tropical conditions and I am guessing the humid conditions made the silver from the wires flow from the wires out onto the surrounding background enamel. That silver was been easily wipe off with a plain cloth rag. However, a residue remains and forming a gray cloud around the design. i believe particles of the silver were deposited into the fine pits left over from the original cloisonné firing process. Is there nay way to get the rescue out of the pits?
Silver marked as “Reinforced” should never be put in hot water (the reinforcing material melts -compromising the structural integrity of the silver object). This method should only be used on “Sterling” silver.
Got an odd question. I have a slightly tarnished silver spoon in our everyday flatware drawer. I take KI daily for medicinal reasons. We were out of spoons, so I used this silver spoon to take the KI solution. It tasted “sulfury”. Can you tell me what happened? I assumed that the “I anion” stripped the silver sulfide. I can’t imagine that I ingested much, but that won’t be happening again. Just curious. Thank you from an embarrased former chemist.
I got a good one, when silver tarnishes like on a coin will it affect the weight of the coin either causing it to weigh more or less, thanks
The simple answer to this question is that silver tarnishes because it reacts with sulfur in the air. However, there are a few other factors that can contribute to silver tarnishing, such as humidity, body chemistry, and contact with other metals.
How to clean tarnished silver easily? (https://www.awsomesolution.in/blogs/how-to-clean-tarnished-silver-easily)
Sulfur in the air is the most common cause of silver tarnishing. When silver comes into contact with sulfur, a chemical reaction takes place that produces silver sulfide, which is the black substance you see on tarnished silver.
Humidity can also play a role in silver tarnishing. Silver is a metal that absorbs moisture from the air, so if the air is particularly humid, it can speed up the tarnishing process.
Body chemistry can also affect how quickly silver tarnishes. Some people have skin that is naturally more acidic than others, and this acidity can cause silver to tarnish more quickly when it comes into contact with skin. Additionally, some cosmetics and perfumes contain chemicals that can speed up the tarnishing process.
Finally, contact with other metals can also cause silver to tarnish. This is because when two different metals come into contact with each other, they can create an electrical current that causes a chemical reaction known as galvanic corrosion.
Could one use a dishwahing machine with aluminium foil set to touch each piece and a hot short (30min) cycle with baking soda as thedishwashing powder?