Cobalt-Lead Glass Filled Sapphire | Gemopedia

Cobalt-lead glass filled sapphire has been filled through a process similar to "infilling" using lead glass. Performed at low heat, this is a less durable treatment and should be treated gently, avoiding household and professional chemicals. This treatment, which uses cobalt-colored lead glass, improves clarity, color, and may add weight through the filling of voids and fissures.
Colors
Blue

Cobalt-Lead Glass Filled Sapphire Classification

Common Name

Cobalt-Lead Glass Filled Sapphire

Species

Corundum

Variety

Sapphire

Colors

Blue

Alternate Names

Gemstone Groups

Key Separations

Chelsea filter reaction, dark field magnification, RI, birefringence, pleochroism

Comments

The stone is cobalt blue instead of the natural blue of sapphire. Lead glass will be damaged with jeweler's torch or exposure to chemicals. Specific gravity can be increased to to the amount of glass in the stone.

Cobalt-Lead Glass Filled Sapphire Optical Properties

Transparency

Transparent - Opaque

Refractive Index

1.762-1.77

Birefringence

0.008-0.01

Optic Character

Uniaxial

Optic Sign

Negative

Polariscope Reaction

Doubly Refractive (DR)

Fluorescence

SWUV: inert
LWUV: inert

CCF Reaction

red

Pleochroism

Dichroic, violet blue and greenish blue

Dispersion

Strength: moderate fire Value: 0.018

Comments

Cobalt-Lead Glass Filled Sapphire Chemistry & Crystallography

Chemical Name

aluminum oxide

Chemical Formula

Al2O3

Synthesis

Crystal System

Trigonal

Classification

Oxide

Nature

Natural

Crystallinity

Crystalline

Comments

Cobalt-Lead Glass Filled Sapphire Characteristic Physical Properties

Hardness

9

Streak

White

Specific Gravity

3.95-4.1 Typical:4

Toughness

Poor

Inclusions

Cobalt-lead glass filled sapphire will have gas bubbles and will display purplish red flash colors from the lead glass filling. There will be color concentrations in the fissures of the stone.

Luster

SubAdamantine

Stability

Poor

Fracture

Conchoidal

Cleavage

None

Comments

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