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All silver tarnishes when exposed to moisture or air. Sulfur is plucked from both air and water to form silver sulfide, which is that grey or black staining you see on silver coins, jewelry or ornaments.
Luckily, it is really easy to clean them up using nothing more than just an electrolyte solution and silver foil. This method only takes minutes, is easy and safe to do, and does not in any way damage the silver.
Note: If your silver coins are valuable for anything more than their silver content, do not bathe the coins in this way. You risk removing the patina on the coin, which some collectors want to see.
What Is Patina?
The patina is that layer of verdigris or tarnish that builds up on the facings of old coins. Very few coins that have been found underground or under the sea are valuable, as years of both use (before it was lost) and subsequent oxidation renders them almost valueless as their faces are worn smooth.
This is not so with silver coins. Silver, even today, is a valuable commodity and silver coins are worth many times more than their face value.
The coin shown here is a 1917 half crown that I found while beach metal detecting. It is rough and corroded-looking, as well as being covered in silver sulphide (sulfide in the US).
Things You Will Need to Clean Silver Coins in Baking Soda
You will need:
- A non-metallic container
- 1 cup of very hot or boiling water
- ½ cup of sodium carbonate (this is sold as washing soda in the US or soda crystals in the UK) or baking soda (sodium bicarbonate) or salt (sodium chloride).
- A strip of aluminum foil
Instructions for Cleaning Silver Coins
- Place the aluminium foil in the bottom of the container. It doesn't have to cover the base, but it does need to be big enough to place the coins on.
- Make sure the coins are touching the foil.
- Add the washing soda. If you have none in, you can substitute sodium bicarbonate, or even sodium chloride (table salt). All the salt solution does is create an electrolyte solution to carry the ions that are moved around during this process.
- Add the hot water. While you can use cold water, the electrochemical reaction is faster in hot water.
- It will all fizz up,and you may have trouble seeing what is happening inside.
- Resist the temptation to look directly in to the top of the solution, because the chemical reaction releases hydrogen sulphide (sulfide), which is a poisonous gas, which you wouldn't want to breathe in.
- When the solution calms down and all the bubbles disappear, you will notice that the aluminium foil has changed color.
- This is because the sulfides from the coins have been transferred to the foil. At the same time, the silver sulfide on the coins have been converted back into silver and stays on the coins. This is called an electrochemical reaction.
- The whole process takes about 10 minutes from start to finish.
- Pour the solution off down the sink, where the washing soda will help clear any blockages you may have had.
- Take the coins out.
- If they are still black, you will find that the sulfides on the patinas have been loosened.
- Gently rinse the coins under a running tap, and use a soft toothbrush to take the blackness off.
- Your silver coins will be left shining bright, with all the tarnish removed.
How to Remove Tarnish and Clean Silver Coins
Are Silver Coins Made From Real Silver?
This method of cleaning coins works especially well for silver. Not all silver coins contain any silver. In fact, most, if not all modern-day silver coins contain no silver at all.
This is because world prices of silver have risen so much that hardly any coins have a high enough denomination to hold their value. You cannot have circulating coins that are worth more as scrap metal than their face value. For this reason, the UK took all silver out of silver coins in 1947, and the US followed suit in 1964.
Silver in U.S. Coins
In the early 1960s, world prices of silver rose considerably. Congress decided to eliminate all silver from silver coins and this was fully implemented in 1964. All pre-1964 of the following coins contain 90% silver:
- Half Dollar
The people most likely to come across these silver coins are metal detectorists, and their value is way above their face value because of the rise in the price of silver.
- At today's prices (November 2012) expect to get or pay around $32 per ounce for silver.
- Expect each of the above-named coins to raise 20 times their face value.
- All US 'silver' coins minted since 1965 or later are clad coins. Clad means they are made from layers or alloys of cheap metal.
- Bicentennial quarters released as collections since 1965 contain 40% silver. These coins are all marked with an 'S' and were not intended for general circulation.
- Half dollars minted between 1965 and 1970 also contain 40% silver.
- Collectors mint series half dollars contain 40% silver. They are stamped with an 'S'.
- In the early 80s and again in the late 90s, world silver prices reached $50 an ounce, so it is well worth hanging on to coins containing real silver.
British Silver Coins
All silver coins in the U.K. contained 92.5% silver up until 1920 when they dropped the silver content to just 50%. In 1947, the silver was eliminated completely, and British silver coins are now made of an alloy of steel and cupro-nickel. The half crown, as shown in the photographs above, was made in 1917 and was made from 100% sterling silver.
Sterling silver is a standard established by King Henry II in the 12th century and contains 92.5% pure silver and 7.5% copper. As silver is one of the softer metals, it was common practise before this time to clip the edges of coins, or even to cut them in half, when one was short of small change. Adding the alloy of copper hardened the silver coins, making them harder to clip, as well as helping them to last longer while in general circulation.
Sterling became the standard of British currency. Even today, banknotes say "I promise to pay the bearer on demand five pounds sterling," or ten pounds sterling, depending on the value of the note.
The £1 bank note is no longer in circulation, having been fully replaced by the £1 coin, but at one time the 1 pound note represented 1 pound in weight of sterling silver.
The Half Crown Coin
There used to be 8 half crowns in £1. A half crown was worth 2 shillings and sixpence, or 30 pennies. There were 240 pennies in the £. It would have been written down as 2/6d. A pound in weight is equal to 16 ounces. So each half crown would originally weigh 2oz each (16 ÷ 8). This weight would have dropped as sterling silver prices rose, and by 1917, the year my half-crown was minted, it had dropped to ½oz in weight. As a child in the 60s, a half crown was a treat to receive, and had the buying power of about £10 ($15) today.
In 1949, during a local new road-building project, workers were offered half a crown an hour in wages, and they flocked from far and wide, this being a fantastic wage for the manual labourer at the time. In 1917, this may well have been a week's wages.
Other Ways to Clean Silver Coins
While soaking them in a solution of washing soda for a few minutes is by far the easiest way to clean silver coins, there are other ways too.
- Soak them in a mild acid solution like vinegar, in the hope of loosening off the silver sulfide. This method may take a long time.
- Tumble them in a rock tumbler with a stainless steel media, water and washing up liquid. This does not always remove the tarnish when it has embedded on the coin.
- Use an electrolysis machine to send an electric current through them.
- A very simple way to brighten up old silver coins so that they are easily identifiable with removing their darkened patina which gives them their aged look, is to simply rub them between two pieces of aluminium foil.
There are other methods of general coin cleaning and cleaning metal detecting finds using various household solutions.
But none are better than the simple way outlined above, which quickly and efficiently cleans silver coins, jewelry and ornaments, while retaining all the silver.
The baking soda method does not work so well for non-silver clad coins because they are frequently coated with different oxides which need a different removal method.
Cleaning Silver Poll
Blackspaniel1 on November 28, 2014:
It would have to be an extreme case to clean a coin, and making them shiny is not the same as restoring mint luster. Some collectors will not add a cleaned coin to a collection.
Metal Detectorist (author) on November 03, 2012:
I can't see me ever wanting to part with mine, I am so attached to them! Oh and I've never found anything gold yet...hopefully I will one day.
Lela from Somewhere near the heart of Texas on November 03, 2012:
Although I would prefer having a collection of gold coins, I do truly enjoy my silver ones!