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Message:: [QUOTE="Tom B, post: 1887283, member: 11854"]There are a few things that might be added. Luster is caused by light refraction off of flow lines, but these lines are mostly removed or obliterate on well-circulated coins.  At the EF level the great majority of flow lines have typically been removed and, thus, luster is not present throughout the coin's surface.  A business strike coin that is dipped after the flow lines are already gone will generally look flat, lifeless, oddly white and just plain wrong.  However, many of these same coins, if dipped many years ago, went on to obtain colorful secondary toning that a large segment of the hobby just adores and will pay strong money to obtain. The removal of toning, dirt or grime by dipping does not generally help the surfaces underneath because if they are already damaged then they will stay damaged.  Indeed, any damage beneath toning, dirt or grime often becomes much more visible after a dip.  If you read old coin magazines (old, like 1900-1950) you will find that dipping coins was many times associated with improving apparent grade and was not often thought of as removing possibly damaging contaminants.   People associated a coin without toning or gunk as a coin with a higher grade and these were marketed at higher price levels.[/QUOTE]