Antique Jelly Belly Dragon's Breath Opal in Sterling Greek Key Setting

What collectors call “Dragon’s Breath” opal was first used in jewelry manufacture in the early 1900s. A synthetic stone, it emulates a cross between the Mexican fire opal and jelly opal.
Dragon’s Breath opal is actually Bohemian art glass, and is more equitable to costume jewelry than precious or semi-precious gemstones. Does that mean that Dragon's Breath opals are worthless? No. In fact, synthetic stones can have a high price tag, especially if they're in vintage jewelry or unique settings.
Made entirely of Czechoslovakian glass, Dragon's Breath or "Mexican Opals" were first used in jewelry at the turn of the 20th century. Since then, they've become highly collectible, and rare.
But why? And how were they made? you want to know. Me, too.
Alas, as is often the case with Bohemian art-glass, the exact recipe has been lost to history and cannot be replicated. (Dragon’s Breath has this in common with Saphiret, supposedly mixed with gold.) The Bohemians were and continue to be master alchemists—there really is no better word—with glass. They also invented lead-free crystal, and the exquisitely lavender-blue Alexandrite glass (made from slag mixed with the rare earth neodymium). The only recipe that remains as mysterious as that for Dragon's Breath opal is the Anglo-Saxon recipe for opaque red glass. (In both cases, to this day, nobody knows how they did it.)
It seems that no one can say much of anything provable about these stones, apart from 1) they were invented and produced in Czechoslovakia around 1900, and 2) we know that Dragon's Breath was made by adding a metal to the glass slag, though nobody knows what kind or in what form, much less what quantity.
Oh, those clever Bohemians—they actually TOOK IT WITH THEM.

About vintage: When Dragon's Breath is set in sterling, it could well date to the early 1900s. At that time, Dragon’s Breath stones were most often set in silver. But be very discerning about the style of the siverwork: does it really look Victorian? Or is it more recent and Cambodian, Mexican, or American?
When struck by light at different angles, Dragon’s Breath stones change from red to blue with subtle hints of other colors translating to an overall bright blue or purple hue. Vaporous flashes from within the stones are known as the “breath” from which the name is derived. These stones have no backing and are quite transparent. They have rounded tops and flat backs (typical cabochons), rather than being faceted like rhinestones. Many are round or oval in shape. Later pieces of classic costume jewelry, made primarily during the 1950s and ‘60s, also used decorative glass stones declared incorrectly by sellers as Dragon’s Breath. These are actually foiled glass cabs rather than true Dragon’s Breath stones. If you see foil on the back of a stone, it’s not really Dragon’s Breath.
This brooch is bounded by a sterling halo of attractive Greek-key motif. Including its setting, the brooch measures 1 & 5/16" (33.34mm) wide and 7/8" (22.2mm) tall. The stone, which by itself measures 24mm (.94") wide by 14 mm (.55") tall is a dome-shaped cabochon about 7mm (.27") thick at its center. DISCLOSURE: On close examination, I see there are two small crescents of glass missing from one end, very probably a manufacturing flaw, as they're beneath the cab setting's "collar"—an unlikely place for chips, since it is protected from impacts. This small shortcoming is shown in photos 7-9. Price reflects major reduction for this.
The pin on this brooch is a simple hook-catch clasp, indicating 19th-century vintage. (The rolling C-clasp became standard equipment shortly after it was patented in 1900.)
Altogether magical and mysterious, to boot, are authentic Dragon's Breath pieces. I think I'll try to find more of these. Writing this one up, it has thoroughly bewitched me.
Weight: 6.4 grams.