Turquoise Jewels with Diamonds| Jewellery |Fürstin Therese von Thurn-Taxis | Schmuck
Turquoise Jewels with Diamonds| Jewellery |Fürstin Therese von Thurn-Taxis | Schmuck
Turquoise and Diamond Parure
The parure from the 1840s, mounted in silver and gold, "comprises a necklace with detachable bow centre-piece, a pair of flaring bracelets, a larger, two medium-sized and two small bow-knot brooches, all set with oval turquoises flanked by courses of rose diamonds, the necklace also with diamond floral motifs. This parure was offered at the famous auction at Sotheby's Geneva 17 Nov 1992.
The Turquoise and Diamond Brooch/Bracelet Clasp or Necklace Front Clasp
In the portrait above, Fürstin Therese von Thurn und Taxis, painted in 1833 by Stieler, is wearing a large three strand pearl necklace with an clasp of turquoise and diamonds.
"Designed as a larger central oval cluster set with a turquoise within a two-row border of smaller turquoises and cushion-shaped diamonds, flanked by two detachable similarly set smaller clusters (one turquoise has been replaced with glass)."
The tripartite clasp probably had an alternative function as a bracelet clasp with a band formed of strings of pearls. Several designs for variants of the three-part construction are known from Köchert.
This complex clasp was made for a triple-row pearl necklace worn by Fürstin Therese von Thurn und Taxis who was born the Duchess of Mecklenburg-Strelitz (1773-1839). She was aged sixty when Stieler painted her portrait. Like her sister Queen Luise of Prussia, she was well-read, artistic and enthusiastically involved in the politics of the day. As wife of Fürst Carl Alexander, she staunchly defended the interests of the House of Thurn and Taxis at the Vienna Congress of 1815.
The set was later testet from SSEF and the following details are:
A set of six antique brooches, set with diamonds
and light blue cabochons, was investigated with microscopy, Raman analysis, and EDXRF spectroscopy. Most of the cabochons proved to be
fossilized dentine, also known as odontolite (mineralogically, fluorapatite). The brooches also contained turquoise and artificial glass.
It has been widely used in
jewelry in the Middle East (Egypt and Persia), the Far
East (Tibet, Mongolia, and China), and by native
North Americans (Ahmed, 1999; Chalker et al.,
2004). Yet turquoise was once very fashionable in
Europe, especially during the 18th and 19th centuries , so it is not surprising that imitations were used when genuine
turquoise was not available. The wide range of
turquoise imitations includes secondary minerals
from copper deposits such as chrysocolla, dyed minerals such as magnesite or howlite, and artificial
materials such as glass or sintered products (Arnould
and Poirot, 1975; Lind et al., 1983; Fryer, 1983; Kane,
1985; Hurwit, 1988; Salanne, 2009).
In this study, we report on a historic turquoise
substitute—fossilized dentine, also known as odontolite, ivory turquoise, bone turquoise, or French
turquoise. Much of this material consists of fossilized mastodon ivory from Miocene-age (13–16
million years old) sedimentary rocks of the Gers
District between the Aquitaine and Languedoc
regions of southwestern France (Reiche et al., 2001).
The tusks are hosted by alluvial sediments (molasse
alternating with fine sand and clay facies) that accumulated in basins during the erosion of the nearby
Pyrenees Mountains (Crouzel, 1957; Antoine et al.,
1997). The fossilized dentine consists mainly of fluorapatite, Ca5(PO4)
3F; since medieval times, local
Cistercian monks have used a heating process to
turn the material light blue (de La Brosse, 1626;
Réaumur, 1715; Fischer, 1819), which they thought
to be turquoise. These “stones” were originally set
in medieval religious artifacts, but came into fashion
in the early to mid-19th century (Brown, 2007),
Odontolite is fossilized dentine (mastodon ivory)
from France that has been heat treated to produce its blue coloration.
• This historic turquoise substitute was identified in
a set of six antique brooches set with diamonds.
• A combination of microscopic observation and
Raman spectroscopy was effective for separating
odontolite from the turquoise and artificial silica
glass also present in the brooches.
T he Swiss Gemmological Institute SSEF recently received a set of six antique brooches for
identification (figure 1). These same pieces had
already been presented in Bennett and Mascetti
(2003, p. 102) as turquoise jewelry. They were set
with numerous small rose-cut diamonds and a few
larger old-cut diamonds, but most prominent were a
number of light blue to greenish blue cabochons that
appeared to be turquoise. Visual examination quickly revealed otherwise. C
More about the experts fromSwiss emmological Institute
Source:SSEF; Sotheby's
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