You can tell a coin has been cleaned by looking for altered light reflection (loss of natural luster, "cartwheel effect"), fine parallel scratches (hairlines), a greasy or unnaturally shiny surface, uneven toning, or darkness/crud left in protected areas, all signs that the original surface has been scrubbed, dipped, or rubbed, changing how light hits it compared to an original coin.
It's generally not a good idea to clean coins, especially collectible or valuable ones. Cleaning can damage the coin's surface, remove its natural toning, and significantly decrease its value. Even light cleaning can leave microscopic scratches that collectors and dealers will notice. If a coin looks dirty or tarnished.
Spotting the Difference at a Glance
Circulated coins typically display surface scratches and minor nicks from handling, whereas uncirculated coins retain a clean, sharp appearance. Luster also matters. Uncirculated coins shine with a brightness that circulated pieces lose over time.
Luster is often diminished or completely removed during cleaning, leaving the coin with an unnatural appearance. It's important to note that cleaning a coin can significantly reduce its numismatic appeal, as collectors generally prefer coins with their original surfaces intact.
Visual Appearance and Production
Regular coins are struck once, giving them a clean and complete finish. Proof coins, on the other hand, are struck twice. The difference in the production process is a more defined, intricate and shinier appearance in Proof coins.
Fill a plastic container with distilled water and stir in the mild hand soap in which you will soak the dirty coins for 10 to 15 minutes. After this, take the coins out, lay them on a clean, soft cloth, and use the old, soft toothbrush to scrub each coin gently.
Burnished coins appear less shiny with a matte finish, compared to a standard bullion coin finish. This is due to the specially polished coin blanks that are used to earn the burnished designation.
Ultrasonic Cleaners
These coins are cleaned by using distilled water with a small amount of detergent in a special vibrating container. Acid based cleaners will eat away at a coin's surface diminishing its value.
Cleaning an old coin would remove the patina or toning that helps make it even more unique and visually appealing. Removing this effect can significantly reduce the value of the item. The other main reason you shouldn't clean old coins is that you can easily damage them.
Acid (Vinegar or Lemon Juice)
Soaking coins in an acidic liquid such as vinegar or lemon juice will clean them, but the acid will also eat away at the coin's surface. Again, this method will reduce the value of collectible coins, so only use it on coins that are valued for their silver content.
While you may be tempted to polish your coins to make them look shiny and new, proceed with caution. Polishing and/or cleaning coins can reduce their value.
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Cleaning almost always decreases value by removing historical patina and causing invisible damage. Patina and “grunginess” are good. What looks like tarnish or dirt is often a sign of authenticity and provenance, especially with historic rare coins. Even gentle cleaning risks harm.
The oil-base makes WD-40 reasonably effective at removing it without a lot of work. There is of course some sacrifice when this stuff is removed but fortunately the metal underneath is in pretty good condition and the coin, in hand, is much more presentable.
Polishing Silver
The most common is using a soft towel and a silver polish cream like Hagerty's or Miror. Another option is to line a ceramic or glass (never metal) dish with aluminium foil. In a separate bowl, mix together one tablespoon of salt, one tablespoon of baking soda, and half a cup of white vinegar.
Surface scratches: If you notice fine lines or scratches that look like they weren't made by the minting process, that's a clue. Overly shiny appearance: As you've noticed with your 1921 Silver Dollar, a coin that looks excessively shiny might have been cleaned. The original luster is usually softer.
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The natural toning or patina that forms on coins over time adds character and history. If you must clean a coin due to dirt or grime, use only a soft cloth or cotton ball with lukewarm water. Never use harsh chemicals, abrasive materials, or polish, as they can damage the coin's surface and affect its value.
Generally speaking, proof coins have a higher relative mark-up than uncirculated coins. As a collector's item, proofs can be sold for more than the value of the raw precious metals they contain. However, the downside is they cost a little more than uncirculated coins to purchase.
All Proof coins since 1968 have been struck at the San Francisco Mint and feature the coveted “S” mint mark.
An uncirculated coin will have crisp, well-defined features without wear on the highest points. These points are often hair, chests, and wings of birds, but every coin is slightly different. If uncirculated, the original mint luster should travel across all parts of the coin.