The red spots that sometimes appear on gold pandas and other gold coins are the result of very small amounts on impurities on or near the surface of the coin that oxidize over time. Although Panda gold coins are 99.9% pure gold, the 0.1% is responsible for the red spots. These impurities can get on the coin from the die or other tooling used to make the coins, or there could be impurities in the gold that gather near the surface. The impurities may not be visible when the coins leave the mint, but exposure to oxygen over time can make the the impurities oxidize and change color.
Are Red Spots Bad?
Red spots are the subject of some debate among collectors and coin grading experts. The major coin grading services like PCGS and NGC consider the spots to be "toning" which is generally not a major factor in determining the grade of a coin. The spots are not considered a defect or damage. Therefore, the measles-like coin at left could grade MS69.
Many Panda collectors, however, try to avoid coins with spots like, well, like the plague! Spots are present on coins still in the mint plastic, especially after they are several years old. To make matters worse, they can be hard to see through older mint plastic sleeves which are not adequate to protect the coins over years. The only way to avoid the spots is to look at the coin carefully before you buy it, and then make sure it stays in a sealed holder away from heat and humidity.
When buying online, make sure listing includes pictures that are clear enough to show any spots, and don't be afraid to ask the seller or dealer if there are spots on the coin. Mint sealed coins often have spots and it can be hard to see through the plastic, so we recommend buying certified coins where the condition of the coin is clearly visible through the optical quality plastic holder.