(Hi ! I am a beginner at shelling. I don't understand some terms on this hobby. May be some one can help me out ! For example, what is gem quality on shell, is that means it has no scar or good color ?)
"gem" means flawless, an absolutely perfect specimen with no defects discernable, even upon close inspection. "fine" means minor flaws, either natural (like scars from healed injuries) or post-collection damage (minor chips on the lip of a cone shell, or fine scratches on a cowrie) which do not greatly detract from the scientific or aesthetic value of the specimen, and which are not readily apparent except upon close inspection.
"good" means that major defects are present, but the principle identifying characteristics of the species are still intact.
"+" can be used to represent grades intermediate between the principle grades mentioned above. "fine +" means "better than fine, but not quite gem". "Fine++" would mean "virtually gem", for example one minute flaw that would be difficult to find, even upon close inspection. "Good +" means better than good, but not good enough to be listed as "fine".
Some dealers use additional "+" signs – "fine +++", which makes the point that the shell is virtually gem, but I personally think it gets a bit silly after two "+" signs. A shell that is "fine +++++++++" should just be listed as "fine ++". That makes the point adequately. Now and then someone uses "gem -", which really means the same thing as "fine ++".
The system is somewhat subjective, and one dealer's "fine++" is another dealer's "fine+". After a bit of experience, you learn just how meticulous a particular dealer is in his grading of specimen shells
(Answer by M. Paul Monfils via the Forum)