Gem Cutting

A character with this proficiency can finish the rough gems that are discovered through mining at a rate of 1d10 stones day. A gem cutter derives no benefit from the assistance of nonproficient characters. A gem cutter must work with a good light source and must have an assortment of chisels, small hammers, and specially hardened blades.

Uncut gems, while still of value, are not nearly as valuable as the finished product. If the cutting is successful (as determined by a proficiency check), the gem cutter increases the value of a given stone to the range appropriate for its type. If a1 is rolled. the work is exceptionally brilliant and the value of the gem falls into the range for the next most valuable gem (the DM has the relevant tables).

Dwarves Gem-Cutting Proficiency

A dwarf with this proficiency may cut 2d8 gems per day instead of 1d10. He also has a greater chance of increasing the value of a gem. If a dwarf rolls a 1 or a 2 during cutting, he increases the value of the gem to that of the next most valuable class (see page 134 of the Dungeon Master's Guide). For example, Duram is cutting a fancy stone with a finished value of 100 gp. He does an exquisite job and actually increases its value to that of a precious gem with a value of 500 gp.

Any character who fails a gem cutting roll cuts the gem, but does so poorly and reduces its value to the next lower category. Duram, flushed with success, tries his hand at a precious stone with a finished value of 500 gp but he slips with his chisel and reduces its value to that of fancy gem (value 100 gp).

A character who rolls a 20 when cutting a gem splits it in half and ends up with two uncut gems with a combined value one class lower than that of the original gem. Duram starts one more gem. It has a value of 50 gp. He places his cutting clamp, over tightens the jaws, and splits the gem in half (he rolls a 20!). He now has two uncut gems with a value of 5 gp each.

[Player's Handbook]
[Complete Book of Dwarves]