Summary
Question: I see gem cutting acronyms like L/W, C/H, and P/H in faceting diagrams. I’ve also seen TCP and PCP in some manuals. What do these terms mean?
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oval-cut pink sapphire - gem cutting acronyms

This 0.82-ct pink sapphire was cut to an oval design with a L/W ratio of 1.2. © James Allen. Used with permission.

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

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.

L/W ration - gem cutting acronyms

The cut design of this faceted zircon, “1.40 Roval,” has a L/W ratio of 1.414. Gem faceted by Jeff Graham.

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.

facets - gem cutting acronyms

Facet terminology

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.

Happy faceting,

Donald Clark, CSM IMG

lapidary lessons - gem cutting acronyms

“Lapidary,” photo by Lenore Edman. Licensed under CC by 2.0.

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