25×18 mm oval black glass cabochon with a high-reflectance mirror finish. Material: high-density glass. Pieces uniform in color and dimensions for artisan jewelry, costume jewelry, and cabochon settings. Industrial component with consistent production.
Piece Details
| Material |
Black glass (soda-lime glass or borosilicate, opaque finish) |
| Dimensions |
25×18 mm oval · tolerance ±0.3 mm (industrial production) |
| Shape and Back |
Oval, flat back |
| Finish |
Mirror polished |
| Hardness |
Approx. 5.5 Mohs (glass) |
| Origin |
Industrial manufacture; jewelry component |
| Treatment |
Color in mass (not a surface layer) |
| Piece Type |
Serial component — high uniformity between pieces |
This Specific Piece
Well-polished black glass exhibits higher reflectance than most black minerals (onyx, obsidian) because the surface can achieve a finer polish in industrial production. The result is a "black mirror" surface that reflects the surroundings with a quality similar to volcanic obsidian but with perfectly uniform dimensions batch to batch. In costume and fashion jewelry, this uniformity is an advantage: earring pairs, bracelet sets, or batches for mass production require interchangeable pieces that natural minerals with individual variations cannot guarantee.
Black Glass vs. Obsidian: Practical Differences
Both soda-lime glass and volcanic obsidian are amorphous glasses of siliceous composition, but they differ in origin, composition, and working properties. Obsidian forms from the rapid cooling of silica-rich volcanic lava (70-75% SiO₂) and contains inclusions of accessory minerals that produce optical effects such as silver sheen or cat's eye. Industrially produced soda-lime glass is optically clean, perfectly opaque, free of inclusions, and calibrated in dimensions.
What Mounting It Works For
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Bezel setting (925 silver, brass, copper) — The industrial calibration of the glass ensures the bezel closes.
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Adhesive cabochon settings — The flat back and precise 25×18 mm dimensions fit.
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Wire wrap — Possible with extra caution on the edges: glass with.
Black Glass in the History of Ornament
Black glass as an ornamental material predates modern industry: Anatolian obsidian glass was one of the first trade materials of the Neolithic period (c. 8000 BCE). Whitby jet, from England, reached its peak production in the Victorian era as mourning jewelry material (1860-1890), and 19th-century artisans already used molded black glass as an accessible substitute for jet. In contemporary fashion jewelry, the black glass cabochon is a standard component in mid-priced costume jewelry collections, where piece uniformity is a production requirement.
In Western symbolic tradition, black associated with obsidian or black glass is linked to protection, introspection, and boundaries. Used in intention jewelry, it is considered a material that "absorbs" what is not needed.
Symbolic properties belong to cultural traditions. They are shared for educational purposes, not as medical advice.
How to Distinguish Black Glass from Obsidian or Onyx
Industrial glass is perfectly uniform: under magnification, there are no inclusions, streaks, or variations in transparency. Obsidian, although also glass, usually shows microflows of volcanic melt and sometimes mineral inclusions. Black onyx (chalcedony) is colder to the touch and has a slightly rougher texture under magnification compared to the total smoothness of polished glass. Industrial glass is slightly lighter than chalcedony (density ~2.50 g/cm³ vs ~2.60 g/cm³). With a metal point, black glass scratches more easily than onyx or obsidian.
Frequently Asked Questions
Is it glass or mineral?
It is industrially produced glass (soda-lime or borosilicate), not a natural mineral.
Are the dimensions exact for stamped 25×18 mm bases?
Yes. The 25×18 mm dimensions are standard for stamped cabochon bases. The industrial tolerance of ±0.3 mm ensures compatibility.
Is the black color stable?
Yes. The color is in mass (not a surface layer), so it does not fade over time.
