Whenever you find a coin that is rare or unusual, it's natural to send it away to have it graded to see how much it's worth. You may be disappointed to receive a lower grade than you expected if the coin looks like new but has flaws and damage that are hard to spot with the naked eye. Be aware that these five flaws are some of the most common reasons for a reduced grade on an otherwise quality coin.

Dark or Black Streaks

Does your coin have an obvious dark streak across all or part of its face? This is called a carbon streak, and it's caused by reactions between the coin's metal and the environment around it. Common causes of carbon streaks include

• Exposure to moisture
• Being stored around airborne contaminants like cigarette smoke
• Residue like ink, paint, or grease.

Marks caused by the first two causes are impossible to remove without further damaging the coin, and even grease can be tricky to remove without compromising the finish. Streaked coins are still valuable due to their other features, but obviously such a visible flaw causes a lower grade.

Shiny Finishes

It seems natural for a coin with a bright and shiny face to get a higher grade than a dingy, old-looking one, but unfortunately, most valuable coins that shine were cleaned improperly. Only certified uncirculated coins should look like new. Scrubbing or dipping a coin in acids to restore its original color and luster greatly reduces the value, and it's one of the most common mistakes made by amateur coin collectors. Even a light scrubbing will affect the final grade the coin receives, and ultimately its collectible value. Professionally restored coins aren't shiny and new-looking, no matter how well-cleaned and polished.

Detail Wear

Even with a magnifying glass, it's hard to tell the difference between a perfectly sharp and a slightly worn detail on a coin until you have years of experiencing in grading. Even perfectly legible lettering and crisp-looking laurel leaves can have just enough wear on them to downgrade the rating of value. If you're absolutely certain that the coin doesn't have any wear to it, take your coin to a separate grading service. If two or three different graders all point out minor wear on the coin, it's a real issue and not simply someone trying to haggle you down in price.

Tiny Repairs

It was a common practice for centuries to turn rare coins into jewelry by drilling holes in them, but many people who inherited those pieces of jewelry realized the coins alone were valuable and had the holes filled professionally to restore them. A coin with a repair of any kind will definitely receive a lower quality grade. Even the most skilled professional repairs are visible during a detail inspection. If the coin is rare enough that very few or no intact specimens remain, it may not matter much that the coin does have a lower grade when it comes down to the price it fetches.

Subtle Discolorations

Most people, even with no knowledge of coin values or collection, know that a badly discolored coin is not worth as much as a good-looking one. However, a pitch black penny with great detail will usually qualify for a higher value than a quarter with very subtle patches of blue and brown. This is because the first form of discoloration is natural and expected, while the second is most likely caused by a person trying to make the coin look more valuable. Intentional discoloration tends to rate a greater loss of grade than natural changes in metal surface color, especially since the dipping or treatment that causes discoloration also affects the long-term stability of the metal.

Check out the webpage of a coin grading service for more information.