The finish of a diamond is an aesthetic term and is not directly related to the diamonds value. If you are buying a diamond, most commercial diamonds are usually polished and have a nice finish. Diamonds are mined, cleaved and created for the commercial market, by the time they are set on a ring, your diamonds finish should be near perfect as possible. You may just need to have it cleaned every few months for maximum beauty.
Many people attribute finish to the end result of diamond treatments. Diamond treatments specifically coating a diamond to change its color can conversely affect the value of a diamond by trying to make the diamond appear a color it is not. Unfortunately diamond coatings are mainly used to deceive the buyer; however there are times when a buyer would like to coat their faint yellow or grey stone to a much more acceptable color.
The diamond coating used is usually very durable and if you don’t know that your diamond has been coated, it may be years until you find out when the coating dissipates. Usually the test to see if a diamond has been coated is for a professional appraiser to clean the diamond and then use a torch on the diamond to expose any coating that may be present.
As for a normal diamond, the finish can be smooth or a little granular, neither of which makes the diamond more valuable, it is just the personal preference of the buyer.
