Diamond Polish:

Diamond polish refers to the lines between the facets tha are left from the cutting process.  The lines are called Polishing lines or polish lines.  They seperate the facets. 

An exaggerated example of a polishing line is the diamond girdle.  The diamonds girdle is nothing more than a big polishing line that seperates the top portion (crown) from the bottom portion (pavillion) of the diamond.  The girdle is an exaggerated example because it is almost always a very big polish line, so big that it is almost always visible to the naked eye.  It is sometimes polished or faceted so as to not be so noticeable.  Most polishing lines are not so noticeable. 

There are many grades of diamond polish but most laboratories use the GIA polish scale:

Excellent:  You cannot even see any polish lines with a 10X magnification loupe.  The diamond is flawless on the outside.  You should know that pits, nicks, scratches, bruises, parcel chap and other surface blemishes, may not affect the Polish grade of the diamond but may be mentioined in the Comments area of the Certification.  Some Laboratories call this grade Ideal, but that is not to be confused with the diamond cut grade of Ideal. 

Very Good:  Has a few polish lines that can be viewed through a 10X loupe, but cannot be seen with the naked eye.  This grade will save you the premium that you would spend on a  Grade of Excellent, but will for all practical applications, look absolutely the same. 

Good:  This grade provides the most bang for the buck.  There are many polish lines on the diamond, but you will still need 10x magnification to see most of them.  Occasionally one or two of these polish lines may be visible to the naked eye, but they are still so small that they are not apparent and since they are clear in color and in between facets, they will usually blend right in nicely.  This is the lowest grade we like to see people go with. 

Fair: Several Polish lines are eye visible.  They are still not very noticeable since they are camoflaged between the facets.  At this point the diamonds brilliance, Sparkle and Fire will start to be affected, to a small degree. 

Poor:  Has many eye visible Polish lines.  You can see the white lines between the facets if you look closely.  This affects the Brilliance, Sparkle, Fire and overall beauty of the diamond.  In some cases, the diamond may look slightly cloudy as a result of the gap's between the faceted surfaces. 

Our Recommendation: If you are looking for an Ideal Cut Diamond, Ideal cut diamonds are supposed to have a grade of Excellent for polish, Excellent for symmetry and have no flourescence.  If it has anything but those grades, it is not an ideal cut diamond.  Even if it has Ideal Cut Proportions. 

Many jewelry stores sell diamonds as "Ideal" that have near ideal proportions, but have less than ideal Polish, Symmetry and may or may not have Fluorescence.  These stores will generally try to sell these diamonds at a premium Ideal cut price. 

Whether you are looking for an ideal cut, premium cut or an off make, you can save a little money by going with a lower polish and Symmetry grade.  We suggest that you go with a grade of at least good.  You probably will not be able to tell the difference between a diamond with good polish and excellent polish.  If you hold them both right next to each other, the Excellent should have slightly more life to it, but the difference is for the most part negligible. 

AGS:  AGS is another independant gemological laboratory.  If you are looking at an AGS Report, they use a different scale than GIA.  It goes from Zero to Ten, with Zero being the best.  Zero is comparable to a GIA grade of excellent.  We suggest that you go with a grade of 5 or better.  4 or better if you can swing it. 

Other factors to consider are Symmetry, Fluorescence, diamond cut and quality of rough.