Gem Focus February 2022: Blue John of England
*Gem Focus & Market Pulse (Free Subscriber)Blue John of England; One of the Most Revered Carving Materials from the British Isles
Fluorite with its bright colors and contrasted banding in aggregate form is a favored carving material. While mineral collectors are attracted to its large, transparent single crystal specimens, the same crystals are faceted for both collectors and jewelry designers, especially in vivid colors. Surprisingly, one type of fluorite that has been mined and appreciated for centuries does not come in such vivid colors. It has rather dark purple and subdued yellow bands with transparent to translucent structure. The name Blue John derives from French “bleu et jaune” (blue and yellow) referring to the main colors of this material that comes from long time fluorite producing mines of Derbyshire in England. There are plenty of references to the mines in Derbyshire published in the 18th century. Although one of them claims that the mines were discovered by the Ancient Romans, there is practically no evidence or record as such, therefore it is thought to have been written to create sensation at the time. The estimated production of Blue John in the 18th century was almost 20 tons per year. The rough blocks were so big that they were used as fireplace panels in mansions. Such examples still exist to tell the tale. In time, the rough production decreased gradually. Today, the production is no more than half a ton per year but the area and the mines are a major tourist attraction. Local and national jewelers of England treasure the authentic material and offer it in both silver and gold jewelry.
Courtesy of Heritage Auctions.
Fluorite has a low durability due to its low hardness and four directional cleavage. However, large pieces of massive fluorite, such as Blue John, is a favorable material for carving. Historically, large Blue John finds were carved into vases, urns, and decorative bowls, whereas the smaller pieces were utilized as small desk ornaments, silverware handles and candle holders. Transparent to translucent structure would help purple, yellow, and white banding to be emphasized in carved objects. The final effect is unmistakably unique to Blue John.
A Pair of Louis XVI-style gilt bronze mounted Blue John cassolettes with ram’s head handles, late 19th century. Courtesy of Heritage Auctions.
Blue John is lightly heated to dry it out and treated with resin, then heated in vacuum again to enhance its durability prior to carving. Smaller pieces are cut into tablets and cabochons before turning them into doublets to provide further protection in jewelry. It is not unusual to see even smaller pieces in modern mosaic-like designs. Blue John is an acquired taste in jewelry, yet an old tradition. It is a constant reminder of how cultural and historical aspects effect the value of a gemstone.
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Gold and Blue John bracelet.
Courtesy Treak Cliff Cavern Ltd.