Introduction: Cleaning Silverware

Recently my mother gave me the endowment she was given by her grandmother. It is not much because most was lost during the bombing of Dresden in 1945. A single porcelaine soup tureen from Meissen and a set of silverware survived. The silverware was rusty and tarnished, in this instructable I want to share the process that I used to clean it.

Step 1: Why Does Silver Tarnish?

Silver(Ag) was considered a noble metal by alchemists because it doesn't oxidise with air and moist. What they didn't know was that it reacts with sulfur(S). If they had, then the technology of photography had been found earlier. Apparently they also didn't eat cooked eggs with silver spoons because then the alchemists had seen how sulfur from ovalbumin could tarnish the silver.

Hydrogen(H) sulfide is a trace element in our air and creates a stable connection between the sulfur and silver atoms:

2Ag + H2S <=> Ag2S + 2H+ + 2e-

In fact this oxidation needs oxygen(O), the complete molecular formula looks like:

4Ag + 2H2S + O2 <=> 2Ag2S + 2H2O

The electrode potential of silver decreases from 0.8V to 0.1V and the surface becomes shabby. To reverse this low-energy state and reinstate a clean surface for our silverware, we need to invest energy into the silver.

Step 2: What Can We Do?

Whiting could clean the silver without energy, but this scratches the surface or removes a tiny part of the silver. We could do this with heat if the silverware was made purely of silver. If it was of lower quality (800) then enclosed copper oxidised and coloured it black again. A very good option is galvanising but most silver immersion baths contain thiourea which is teratogenic and carcinogenic. Leave this to experts, especially the waste disposal. Another reason is this procedure enables tarnishing afterwards much easier.

There is a cheaper and safer version of galvanising, with aluminium foil and an acid solution. The aluminium(Al) corrodes and delivers electrons for the corroded silver:

Al => Al3+ + 3e-

3Ag+ + 3 e- => 3Ag

The acid solution generates hydrogen on the surface of the silver:

2H+ + 2e- => 2[H]

Therefor we can redox the silver sulfide (tarnish) back to silver and hydrogen sulfide:

Ag2S + 2[H] => 2Ag + H2S

Of course silver oxide (crust) is reduced to silver and hydrogen oxide (yes, water):

Ag2O + 2[H] => 2Ag + H2O

The complete molecular formula looks like this:

3Ag2S + 2Al + 6H2O => 6Ag + 2Al(OH)3 + 3H2S

Step 3: Rust Removal

Actually silver is too soft to make cutlery of it, knife blades need a steel core for stabilisation. If the thin silver is gone, then the steel can rust its way to the surface. A soft acid like citric acid removes most of the rust, it creates a coordination complex with iron and releases carbon monoxide, water and hydrogen.

Step 4: Citric Acid

The best results can be achieved if the citric acid is heated to 80°C (176°F), use a glove if you do so. Spread some citric acid on a paper towel and rub the rust from the blade. The result is a shiny blade and you can already see the silver coating is gone in some places.

Step 5: Preparation

You need a plastic bowl, aluminium foil, boiling water, salt and baking soda/ sodium bicarbonate. Place the foil into the bowl and put the kettle on. The bowl should be outside because as I already explained this process will release hydrogen sulfide. It will smell like rotten eggs. You don't want this in your kitchen.

Step 6: Salt the Rust

Put the cutlery with the dull side on the aluminium foil. Although most of the rust was removed with citric acid and then rinsed with water, some can only bowdlerized with hot water and salt. Sprinkle salt on the rusty parts, sprinkle baking soda on the silver parts and add the boiling water. It should be around 6 tablespoons of salt and 1 teaspoon of sodium bicarbonate per liter of water.

Step 7: Rotten Eggs

The smell is pretty bad but it can take up to half an hour. Then take the silverware out and dry it with a dishtowel.

Step 8: Silver Care Afterwards

There are products for conservation of silver objects which slow down tarnishing because they absorb moisture and gases like a sponge. A piece of chalk next to the silverware can also absorb moisture and prevent tarnishing. Flannel is said to absorb sulfur and there are pretty flatware rolls made especially for silverware.

Step 9: Result:

In the pictures above you can see a side by side comparison of the final result and the initial condition. The spoons and forks are now in perfect condition. The knife blades have partially lost their silver coating of the steel cores and I will have to bring them to a specialist.

I hope this instructable was helpful and comprehensible. Enjoy your cutlery looking "as new".

Comments

author
parkerpe made it! (author)2017-07-11

I have inherited silver platters that are horse show trophies from 1950's. I have tried silver polish, but years of neglect were not all removable. I will definitely try your process!

author
Joerg Engels made it! (author)Joerg Engels2017-07-11

Good luck! Put them into a glass photo frame with a flannel background.

author
parkerpe made it! (author)parkerpe2017-07-20

Tried it and it worked very nicely on my silver trophies! I wish I had known about this technique before I spent energy using silver polish. Thanks for the lesson and also for the tip about flannel! Now... off to make a frame to display them.

author
slimtender. made it! (author)2017-07-13

Also a mix solution of baking soda + salt is useful instead citric acid

author
Joerg Engels made it! (author)Joerg Engels2017-07-13

Yes, as explained in this instructable.

author
IncognitoA made it! (author)2017-07-12

Awesome, I have a nice silver 70 years old lighter that definitely would need a bit of care, I just hate the smell it leaves in my hand when I play with it.

author
Joerg Engels made it! (author)Joerg Engels2017-07-12

The smell is kind of good, it means the silver kills the bacteria on your skin by the oligodynamic effect. The main reason why silverware was common in ye olde times.

https://en.wikipedia.org/wiki/Oligodynamic_effect

author
LarsO made it! (author)2017-07-11

Thanks for a nice instruction! Do you know if there is any way of detarnishing silver without any fluid? I am asking because I have some. silver instruments that have turned black, and there are parts that should not be wet.

Thanks for any advice!

author
Joerg Engels made it! (author)Joerg Engels2017-07-12

Like I wrote in step 2 you can use a whiting that you buy at a pharmacy. It will make small scratches and you have to tiringly polish your instruments afterwards. Mix it with tooth paste to reduce the scratches while you still have an abrasive. On the other hand the boiling water with salt and baking soda will not cause corrosion on your silver instruments, it is like bringing your tuxedo to a dry cleaner. Or soak a paper towel in the solution and wrap it around the delicate parts, then pour boiling water over it.

Ask your trusted instrument maker!

author
bluejeannes made it! (author)2017-07-11

Thanks for the article. I'd like to try this on a set of silverware handed down from my grandmother, but there is no rust. Do I still need to add salt? If so, does it matter whether it is iodized or not?

author
Joerg Engels made it! (author)Joerg Engels2017-07-11

The main reason why you add salt or natron is because the water needs more ions to streamline the transport of electrons from the aluminium to the silver. Chloride ions (from the salt) decompose catalytically aluminium while carbonate ions (from the baking soda) connect to silver. Both is useful, you could do the procedure solely with one of each. Innocuous trace elements like iodine or fluoride don't matter. Make sure you have chalk or flannel for the storage afterwards.

author
Mickleblade made it! (author)2017-07-08

I wish my chemistry teacher back at school could have taught his subject as well as you do!

author
Joerg Engels made it! (author)Joerg Engels2017-07-09

He probably did but you were too busy swapping notes with the girl next to you ..

author
Mickleblade made it! (author)Mickleblade2017-07-09

oh so true, it's hard for a teacher to make a chemistry more interesting than her when you're 15 yrs old, and you think you already know everything that matters.

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Bio: Polymath and idiot. Mostly idiot.
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