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Ratnapura sapphire pre-forming: identifying dichroism on copper dop sticks with beeswax?

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C
Claire Gem•920 rep

How do traditional gem cutters in China Fort orient rough corundum crystals along optic axes using heated beeswax dops to maximize finished royal blue color saturation?

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6 Answers from travellers

✓Accepted Answer

Corundum is an optically uniaxial mineral with pronounced dichroism: looking down the optic c-axis reveals vibrant royal blue, while looking perpendicular to the c-axis transmits pale greenish-blue. Master lapidarists heat copper or brass dop sticks, apply a blob of melted sealing wax (a blend of beeswax, shellac, and brick dust), and press the rough stone into place. The cutter aligns the crystal so the table facet is ground perpendicular to the c-axis, orienting the deepest blue hue to face out through the crown. Misaligning the axis by 20 degrees produces a finished stone with a muddy, washed-out greenish cast.

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H
Hassan Gem•1890 rep

Dop wax must cool slowly in ambient air; plunging hot brass dops into cold water causes thermal shock that cracks internally strained sapphires.

22
C
Claire Gem•920 rep

Check for natural color bands (silk zones); positioning a small, concentrated blue color patch directly at the culet tip reflects deep blue throughout the entire stone.

18
L
Lukas•915 rep

Pre-forming uses lead-tin laps charged with coarse 220-grit diamond paste, cooled by a continuous water drip to prevent frictional overheating.

15
E
Evelyn Spice•930 rep

Inspect the pre-form through a calcite dichroscope under diffused morning daylight to verify color alignment before cutting crown facets.

13
D
Dev•885 rep

Handheld jambu wooden peg dop sticks are still preferred by elderly cutters for the fine tactile feedback they provide on spinning lead wheels.

10
D
Dev Saline•885 rep

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