Rules: DMG 30.

Note the important message on DMG 30!: “Important: Players should never know the skill levels of jeweler-gemcutters!”

A hireling costs 100 gp/month to employ as a base cost.¹⁾ Jeweler-gemcutters who are not being employed on a monthly basis as a hireling but instead are being hired in a settlement in their own shop for example should simply have this base fee applied for the duration of the service. For example, if a month has 28 days, a hire of 5 days would cost 100 * (5/28), or about 16 gp.

In addition to the base cost, 10% of the value of the resultant gem or jewelry must be paid.²⁾

Some of the process is covered in the rules on DMG 30, but some things are left vague. To solidify:

The jeweler function cannot simply improve the value of an existing piece of jewelry. It is for crafting a new jewelry item out of materials, thereby increasing the value of the materials.

• A success increases the base value of the gem by 1 step.^Ex
• This can only be done once per gem.^Ex
• Gems of 5000 gp base value or greater cannot be used.
• Only gems found while adventuring can be used. They cannot work with such items purchased in settlements or from traders.^Ex3)

The time it takes to cut a gem depends on the target value of the gem (its base value if the cut succeeds):^Ex