Answer: The gem cutting acronyms found in faceting diagrams stand for specific ratios that should help the jeweler determine if the design will fit a piece of rough. Some of the ratios refer to the dimensions of the stone. Others refer to specific facets of the finished gem, such as crown, pavilion, and table.
L/W is the “length-to-width” ratio. This is an important bit of information included in many gem designs so you can get a good idea of how they will fit your rough before you start cutting. For example, if you had a 7 x 5 mm oval-cut gem design, it would have a length-to-width ratio of 1.4 (or 7 divided by 5). You couldn’t cut that design from rough that measures 8 x 6 mm, because it has a L/W ratio of 1.33.
If your rough equals or exceeds the L/W ratio for a design, you can utilize it, because you can always cut and remove gem rough. However, if your rough L/W ratio is smaller than that of the design, you can’t use it. You can’t add material to a piece of rough.
C/H and P/H
C/H and P/H stand for “crown-to-height” and “pavilion-to-height.”
This information will tell you if your rough is deep enough to cut the design.
H/W, T/W, and T/L
You may also encounter gem cutting acronyms like H/W, “height-to-width,” T/W, “table-to-width,” and T/L, “table-to-length.”
These will help you get a better idea of how the stone will develop.
TCP and PCP
The instructions to “cut to TCP” and “cut to PCP” are from meetpoint cutting. TCP means “temporary center point.” PCP means “permanent center point.” A temporary center point is cut to give a reference point for the next sequence of facets. You can find detailed explanations of these terms in Introduction to Meetpoint Faceting by Long and Steele.
Donald Clark, CSM IMG