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J Edit 3 terms found

J
A grade in GIA’s Color Grading System…. at the end of the “Near Colorless” category.
Jewel
A precious stone (usually a synthetic sapphire or ruby) that is used as a bearing for watch gears to reduce friction. The top of the jewel has a depression to hold oil. Jewels are set in the metal plates that support the gears. The pivot (the tip of the gear arbor) goes through a hole in the jewel.
Jump Hour
From Heures Sautantes, a watch where the hour hand is replaced with a tiny aperture at the 12 o’clock position. Through this window one could view a miniature wheel displaying the numbers 1 thru 12. When the minute hand passed the 60-minute mark, the wheel would turn, thus the hour marker jumping into place at the start of each hour.