Gold coin grading is a very important part of determining the value of a coin enthusiast’s collection.
There are many factors to take into account when grading coins.
The quality of the gold coin when it leaves the mint. It is possible, even with proof coins, that imperfections can be found which occurred during the striking process. If there is even so much as a tiny foreign substance between the dies when the coin is struck then that will leave an imperfection. Hairlines can form when someone touches the coin with their bare hands or wipes the surface of a coin or even simply sliding it out of the protective coin holder.
Hairlines are the most common reason why gold coins are downgraded in proof to perhaps Proof-63 and Proof-64 instead of Proof-69 or Proof-70. Anything that touches the surface of the coin can leave hairlines. Hence the extremely high value of old coins that have no surface imperfections, hairlines etc.
Cleaning a gold coin can also adversely affect it’s grading. Unless you know how to professionally clean gold coins, cleaning should be left to a professional. Chemical cleaning can sometimes remove a layer of gold leaving a bright surface underneath but this also can damage the gold coin, particularly a proof coin. This can also be spotted by a professional grader however as can mechanical cleaning where abrasives are used. These will commonly scratch the surface of the coin and reduce the grading and therefore the value.
It is probably wiser to avoid any cleaning whatsoever as the fact of cleaning itself may affect the grading of the gold coin.
For older gold coins the amount of circulation wear or, for an uncirculated mint coin (MS60 through to MS65) how close it resembles a "perfect" condition when first struck.
Proof gold coins are struck in a special way with extra attention to the striking process and these coins are primarily meant for collectors.
All rare gold coins should be independently certified for grade and authenticity by a leading independent grading service, for example:
Professional Coin Grading Service by PCGS and
Professional Coin Grading Service by NGC.
Certified gold coins protect both the buyer and the seller by providing protection and an agreed grading and value for the gold coin.
Gold coin grading is very important to ensure you can demonstrate the true value of your gold coin collection and well worth the small amount it costs to obtain certification.