Mint: Exactly as issued. 

Excellent: Clean back and front, including edges, sharp edges and sharp corners. .

Very Good: Clean back and front, may have dirty and softened edges and rounded corners. No creases.

Good: Soiled on back or front. Blemished edges, rounded corners and one crease. 

Fair: Creased, dirty or with mount damage to backs and possibly some picture surface missing. 

Poor: Badly creased, dirty or with mount damage to backs and surface damage on backs and fronts.