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Purple Glass
| Hardness | 5-6 |
| Specific gravity | 2.4-2.5 |
| Refractive index | 1.50前後 |
| Crystal system | 非晶質 |
Pale lavender (manganese 0.5–1.0 wt%), classical amethyst-purple (manganese 1.0–2.0 wt%), deep royal-purple (manganese-and-cobalt), and the rare neodymium 'alexandrite paste' with characteristic color change purple-blue (daylight/fluorescent) to red-purple (incandescent). Swarovski's 'Amethyst,' 'Tanzanite,' and 'Violet' standard colors remain the global reference shades for costume-jewelry purple.
- Regular round gas bubbles distributed evenly through the matrix — diagnostic of pressed or molded glass at 10×
- Surface molding seams and press-die parting lines on backs
- Color zoning streaks from incomplete batch mixing
- Devitrification crystallites in older or heat-stressed material
- Lycurgus Cup-style dichroic ancient material: gold-silver nanoparticles (~70 nm) visible only by transmission electron microscopy
- Singly refractive (amorphous glass structure) — no
- Refractive index 1.50–1.70 depending on lead content
- Specific gravity 2.4–4.5 — lead-crystal at the high end
- Mohs 5–6 — easily scratched by quartz (Mohs 7)
- Conchoidal fracture
- Neodymium glass: characteristic narrow-line absorption bands diagnostic of f-electron transitions; manganese-amethyst glass: broad-band absorption centered at 540–580 nm
- 01Regular round gas bubbles visible at 10× — immediately diagnose pressed or molded glass
- 02Singly refractive (no ) versus natural amethyst's clear at 30× immersion
- 03Refractometer reads 1.50–1.70 versus natural amethyst 1.544–1.553 (overlapping but diagnostic combined with polariscope)
- 04Mohs 5–6 scratches against a steel knife; natural amethyst (Mohs 7) is unaffected
- 05Natural amethyst: tiger-stripe color zoning, Brazil-law twinning visible under polariscope, and characteristic 'ZebraStripe' angular twinning patterns; glass: regular round gas bubbles and pressing seams
- 06Neodymium 'alexandrite paste' versus genuine alexandrite: refractometer (glass 1.50–1.70 versus alexandrite 1.741–1.755) and examination are decisive
- Mohs 5–6 — stores separately to avoid scratches
- Avoid ultrasonic cleaning — vibration can crack the brittle matrix
- Stable to light and mild detergent; warm soapy water and soft brush
- Avoid thermal shock — conchoidal fracture risk
- Manganese-amethyst paste may show very slow color fading under prolonged UV exposure (over decades) — store away from sustained direct sunlight
Modern molded and faceted purple-glass cabochons trade at $0.30–$3 per piece wholesale (Indian and Chinese mass production); Swarovski Crystal Amethyst, Tanzanite, and Violet components at $0.50–$5 per piece; Czech Gablonzer material at $2–$25 per piece. Neodymium 'alexandrite paste' specialty material from Preciosa and Kyocera reaches $10–$50 per piece at retail. Murano lampwork purple beads in millefiori techniques reach $50–$300 per bead. Genuine eighteenth- and nineteenth-century manganese-amethyst paste trades at $150–$2,500 per piece at vintage and estate auctions.
Note: Disclosure as 'glass' or 'imitation amethyst/alexandrite/purple sapphire' is mandatory under FTC Jewelry Guides §23.25 and CIBJO Blue Book. Beware of neodymium 'alexandrite paste' marketed as 'synthetic alexandrite' or 'created alexandrite' — true synthetic alexandrite (Czochralski-grown chrysoberyl from Kyocera Crescent Vert, Hrand Djevahirdjian Djeva, and other producers) is BeAl₂O₄ with the same composition and properties as natural alexandrite and requires 'synthetic' rather than 'imitation' disclosure. The neodymium color-change is an imitation effect achieved by rare-earth f-electron absorption rather than the chromium chromophore that produces natural and synthetic alexandrite color change. Swarovski 'Tanzanite' color components dominate the costume-jewelry purple market.
Purple glass is amorphous SiO₂-based paste colored purple by various chromophores. Manganese (Mn³⁺ specifically — the manganic oxidation state) at 1.0–2.5 wt% MnO₂ produces the classical 'amethyst purple' tones that dominated nineteenth-century paste production; neodymium oxide (Nd₂O₃) at 0.5–2.0 wt% yields the characteristic color-change 'Alexandrite paste' that shifts from purple-blue under fluorescent light to red-purple under tungsten light, exploiting the same f-electron transition that produces alexandrite's natural color change; manganese-and-cobalt combinations yield the deepest royal-purple tones approximating Madagascan beryllium-treated purple sapphire saturation. Non-crystalline, isotropic, Mohs 5–6, SG 2.4–4.5, RI 1.50–1.70, singly refractive, conchoidal fracture. Industrial production from Bohemian Gablonzer (Jablonec nad Nisou), Murano (Venice), Swarovski (Wattens), Preciosa (Jablonec), and modern Indian and Chinese factories.
Origins
aceted purple-crystal. Italy (Murano, Venice) supplies lampwork beads. France (Saint-Gobain, Baccarat) produced manganese-amethyst paste descended from Strass. Specialty neodymium-color-change 'alexandrite paste' is produced by a handful of European specialty firms (notably Sklárny Bohemia and Preciosa) and Japanese (Kyocera Crescent Vert subsidiary). India (Firozabad) and China dominate twenty-first-century mass production.
History
Roman purple glass reaches its technical apex in the Lycurgus Cup (British Museum 1958,1202.1), a 4th-century CE Roman cage-cup containing gold-silver nanoparticles (~70 nm) in a soda-lime glass matrix that produces dichroism — green in reflected light and purple-red in transmitted light. This dichroic effect was rediscovered and explained as plasmonic resonance only after Gustav Mie's 1908 theoretical work and modern transmission electron microscopy in the 1990s. Pliny's Naturalis Historia Book 36 (c. 77 CE) describes manganese-colored 'amethyst purple' tones. The Venetian Murano tradition (Angelo Barovier, c. 1450) established medieval European purple-glass production. Georg Friedrich Strass's Paris atelier (1730s) introduced manganese-amethyst paste as imitation amethyst — at a time when natural amethyst was a luxury Russian Siberian (Ural Mountains) and Brazilian Minas Gerais commodity. The neodymium 'alexandrite paste' color-change glass was developed independently in Russia (S. Stookey at Corning Glass Works, working on photochromic and dichromic effects in the 1950s, though commercial Russian alexandrite-paste production at NIIES-Severtsov in Moscow region from the 1970s established the modern formulation). Daniel Swarovski's 1892 Wattens factory and Coco Chanel's 1920s collections incorporated purple paste alongside crystal. The 1968 US FTC Jewelry Guides §23.25 disclosure rules apply.
Lore & symbolism
No birthstone designation (synthetic/imitation material). The amethyst tradition — the natural species most often imitated by purple glass — carries strong cultural symbolism: amethyst is the February birthstone, the traditional Episcopal/Anglican bishops' ring stone (from at least the 13th century, codified in the 14th century), and the classical Greek apotropaic against drunkenness (from the etymology 'a-methystos' = 'not drunk'). The Lycurgus Cup is a documented exemplar of ancient dichroic-glass technology preserved at the British Museum. The Bohemian Gablonzer regional craft tradition is preserved under UNESCO intangible cultural heritage.
Tools to confirm this stone
Tools that help confirm Purple Glass. Tap any item to jump to the matching section on the gem tools page.
- 最終確認日
- 2026年4月28日
- 参 考 文 献
- Gem Encyclopedia／ GIA (Gemological Institute of America)
- 宝石鑑別基準／ 中央宝石研究所 (CGL)
- Mineral & Gem Database／ Mindat.org / Gemdat.org
- 宝石学入門／ 全国宝石学協会
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