Ruby – Coconino Lapidary Club

Art Deco Rubies

Mineral Man Mel — Sun, 05 Apr 2020 16:14:00 +0000

Art Deco is my favorite style of jewelry, with its flair of design and the use of unusual combinations of gemstones. Art Deco is a style of architecture and design which first appeared in France just before World War I, reached its high point during the 1925 Paris Exposition of Decorative Arts, and extended into the 1940’s. Today, authentic Art Deco period jewelry and art objects, as well as reproductions, remain esteemed by wearers of jewelry and collectors. In the following gallery I’ve included ruby jewelry and art objects which greatly appeal to me.

RUBY JEWELRY AND ART WORKS GALLERY

Figure 1. Art Deco brooch with carved ruby and surrounding diamonds [Ref 1].

Figure 2. Art Deco diamond and ruby floral cluster setting in a platinum ring [Ref 2].

Figure 3. Art Deco ruby and diamond decorated onyx compact [Ref 3].

Figure 4. Art Deco carved ruby and emerald, diamond, onyx, and enamel
pendant brooch [Ref 4].

Figure 5. Art Deco carved jade, diamond, ruby, and platinum card case [Ref 5].

Figure 6. Art Deco ruby and diamond necklace and brooch [Ref 6].

Figure 7. Art Deco ruby, onyx, and diamond set platinum brooch [Ref 7].

Figure 8. Art deco carved ruby, sapphire, emerald, and diamond “Tutti Frutti” bracelet [Ref 8].

Figure 9. Art Deco ruby and diamond yellow gold watch [Ref 9].

Figure 10. Art Deco carved jade, ruby, and onyx
Pendant brooch [Ref 10].

REFERENCES

Ref 1. http://www.gemscene.com/art-deco.html

Ref 2. https://www.carters.com.au/index.cfm/item/387782-an-art-deco-style-diamond-and-ruby-ring-of-floral-cluster-design/

Ref 3. https://www.pinterest.com/pin/509751251551385459/

Ref 4. https://www.pinterest.com/pin/509751251547056346/

Ref 5. https://www.pinterest.com/pin/94716398384257546/?lp=true

Ref 6. https://www.flickr.com/photos/clivekandel/6839720818

Ref 7. https://www.1stdibs.com/jewelry/brooches/brooches/1920s-art-deco-ruby-onyx-diamond-platinum-canvas-brooch/id-j_1323593/

Ref 8. https://www.christies.com/features/Cartier-jewels-collecting-guide-9582-1.aspx

Ref 9. https://www.1stdibs.com/jewelry/watches/wrist-watches/1940s-art-deco-112-carat-ruby-101-carat-diamond-yellow-gold-watch/id-j_4725961/

Ref 10. https://www.pinterest.com/pin/354799276872845520/

Ancient Rubies

Mineral Man Mel — Fri, 27 Mar 2020 18:44:36 +0000

In this continuation of blogs about the corundum gem varieties, sapphire and ruby, I will first describe the trade routes that first brought the gems, from their mines in the East, to the Roman Empire, then to the rest of Europe. I will also present a gallery of ruby jewelry and artworks designed and made by artisans of the Grecian and Roman Empires and those of the Victorian Era, as well.

ANCIENT SOURCES AND TRADE ROUTES OF SAPPHIRES AND RUBIES FROM EAST TO WEST

As shown in Table I, sapphires and rubies were mined in the East, before 543 BC in what is now Sri Lanka; before 600 AD in what is now Myanmar; before 951 AD in Afghanistan; before 1408 AD in what are now Thailand and Cambodia. Mining began in 1879 in the Kashmir province of India. Interestingly the mines in the East were the sole sources of sapphires and rubies until the discovery of these gems in Madagascar.

The overland and maritime routes of the Silk Road between the East and West served to bring sapphires and rubies from their sources in the East to the Mediterranean, and particularly to coastal cities of the Roman Empire [Ref 1, Ref 2]. The relationship of the port locations serving the Silk Road, to the sources of the gems, are shown in Figure 1. As seen in the figure, sources of rubies and sapphires in what is now Thailand, Cambodia and Sri Lanka, were in close proximity to the ports serving the maritime routes. Trade along the Silk Road, beginning in 2 BC, provided sapphire and ruby gemstones to the Etruscan and Roman Empires, as well as to Europe, later on. Both overland and maritime routes also served to bring the gemstones to the Mughal Empire in what are now India, Pakistan, and Afghanistan.

TABLE I. ANCIENT AND MODERN SOURCES OF SAPPHIRES AND RUBIES

DATE	SOURCE	REMARKS
Before 543 BC [Ref 1,2,3]	Sri Lanka	Gemstones appeared in Etruscan jewelry (700 BC to late 4^th Century BC).
Before 600 AD [Ref 1]	Myanmar (Burma)	Mentioned in ancient legends. Europeans reported source in 15^th century.
Before 951 AD [Ref 1]	Afghanistan	Ruby mines on border with Tajikistan since 10^th century.
Before 1408 AD [Ref 1,4]	Thailand/Cambodia	More sapphire and ruby deposits in Thailand than in Cambodia
1879 [Ref 5]	Kashmir State, India	Blue sapphires discovered in Padar region.
After 1891 [Ref 1]	Madagascar	Sapphire and ruby occurances first described in 1547.
1895 [Ref 6]	Yogo Gulch, Montana, USA	Noted for deep blue color
1950 [Ref 1]	Tanzania	Ruby deposits still being discovered.
1973 [Ref 1]	Kenya	Most important deposit near Mangari in SE Kenya.
1970’s [Ref 1]	Vietnam	First major discovery in province of Luc Yen. Major commercial mining began 1980’s.
2008 [Ref 1]	Mozambique	Deposit found near Zambia border.

GALLERY OF ANCIENT RUBY JEWELRY AND ART OBJECTS

In a search of the web for examples of ancient ruby jewelry and art objects from the Roman and Hellenistic Era to the Victorian Era, I found a dearth of examples of ruby jewelry, in contrast to finding examples of both sapphire and garnet jewelry. Studies from ancient sources show that ruby jewelry was extremely rare and that the red garnet was the most popular gem in the Helenistic Era, but somewhat less popular in the Roman empire [Table, PP 175-176 Ref 1].

Accordingly this gallery presents examples of ruby jewelry and art works from the Medieval Era [Ref 9] to the Victorian Era

Medieval Era

Figure 1. Gold ring brooch set with rubies and sapphires, English circa 1275-1300[Ref 10].

Figure 2. Crown of Princess Blanche with rubies, sapphires, and pearls, English probably 1370-80 [Ref 11, Ref 12].

Figure 3. Reliquary brooch, set with rubies and other gemstones,
Bohemian(?) mid-14^th century [Ref 13].

Figure 4. Ring with ruby and opal set in gold, circa 1300-1325 [Ref 14].

Renaissance Era [Ref 15]

Figure 5. Pendant with baroque pearls and set with rubies, diamonds, and sapphires, known as The Canning Jewel, English, 16^th century [Ref 15, Ref 16].

Figure 6. Portrait frame, worn as a pendant and set with rubies, emeralds and pearls. English, 1547-1619) [Ref 17].

Figure 7. Gold Gimmel Ring with ruby and diamond, German dated 1631[Ref 18, Ref 19].

Figure 8. Enameled gold scent holder (pomander) set with rubies, emeralds, and diamonds, Netherlands 1600-1625 [Ref 20].

Figure 9. Gold snuffbox set with rubies, diamonds, mother of pearl. Berlin, circa 1765 [Ref 21].]

Victorian Era [Ref 21]

Figure 10. Victorian Burmese Ruby and diamond necklace, English, circa 1850 [Ref 22, Ref 23].

Figure 11. Diamond and ruby pendant necklace, French circa 1900 [Ref 24].

Figure 12. Ruby and diamond set gold ring, 1890s [Ref 25].

Figure 13. Ruby and diamond pendant, circa 1900 [Ref 26].

Figure 14. Gold cross pendant set with rubies and
green sapphires with cannaetille work, late Victorian Era [Ref 27, Ref 28].

Figure 15. Dutch East Indies Javanese Royal Presentation cane set with rubies and diamonds, Java 1800-1900 [Ref 28, Ref 29].

REFERENCES

Ref 1. https://www.researchgate.net/publication/236881270_Mining_and_minerals_trade_on_the_Silk_Road_to_the_ancient_literary_sources_2_BC_to_10_AD_Centuries

Ref 2. http://studiopjj.blogspot.com/2007/05/east-and-west-ancient-gem-trade-between.html

Ref 3. https://www.langantiques.com/university/Ruby

Ref 4. https://en.wikipedia.org/wiki/Etruscan_civilization

Ref 5. https://gem-a.com/news-publications/media-centre/news-blogs/gems-from-gem-a/gem/ancient-sapphires-and-adventures-in-ceylon

Ref 6. http://www.lotusgemology.com/index.php/library/articles/276-moontown-a-history-of-chanthaburi-thailand-and-pailin-cambodia

Ref 7. http://www.ruby-sapphire.com/r-s-bk-india.htm

Ref 8. https://gemgallery.com/yogo-sapphire-gemology

Ref 9. https://en.wikipedia.org/wiki/Middle_Ages

Ref 10. https://www.pinterest.com/pin/89931323788019900/

Ref 11. https://en.wikipedia.org/wiki/Crown_of_Princess_Blanche

Ref 12. https://en.wikipedia.org/wiki/Blanche_of_England

Ref 13. https://www.pinterest.com/pin/155937205834052921/

Ref 14. https://www.pinterest.com/pin/155937205826166727/

Ref 15. https://en.wikipedia.org/wiki/Renaissance

Ref 16. https://www.britannica.com/art/jewelry/The-history-of-jewelry-design

Ref 17. https://theframeblog.com/category/16th-17th-century/

Ref 18. http://www.medieval-rings.com/exhibitions/cycles-of-life-35062/rings/renaissance-gimmel-ring-with-memento-mori-42534

Ref 19. https://en.wikipedia.org/wiki/Gimmal_ring

Ref 20. https://www.pinterest.com/pin/370772981794628769/?lp=true

Ref 21. https://www.pinterest.com/pin/335799715956345727/

Ref 22. https://en.wikipedia.org/wiki/Victorian_era

Fig. 23. https://www.pinterest.com/pin/151574343680238550/

Fig 24. http://www.alaintruong.com/archives/2008/10/12/10923843.html

Ref 25. https://www.kalmarantiques.com.au/product/antique-ruby-and-diamond-ring-made-in-the-victorian-era/

Ref 26. https://www.1stdibs.com/jewelry/necklaces/pendant-necklaces/antique-victorian-ruby-diamond-pendant-platinum-circa-1900/id-j_4838913/

Ref 27. https://www.the-saleroom.com/en-us/auction-catalogues/gorringes/catalogue-id-srgo10026/lot-5c8d439e-5052-4618-b7c2-a72f00d0c0ed

Ref 28. https://www.langantiques.com/university/Cannetille

Ref 29. https://en.wikipedia.org/wiki/Dutch_East_India_Company

Sapphire – Art Deco

Mineral Man Mel — Fri, 13 Mar 2020 16:36:32 +0000

Art Deco is my favorite style of jewelry with its flair of design and the use of unusual combinations of gemstones. Art Deco is a style of architecture and design which first appeared in France just before World War I, reaching its high point in the 1925 Paris Exposition of Decorative Arts, and extending into the 1940s. Today, authentic period jewelry, art objects and reproductions remain esteemed by those who wear and collect it. In the following gallery I’ve included jewelry and art objects which greatly appeal to me.

SAPPHIRE JEWELRY AND ART WORKS GALLERY

Figure 1. Art Deco brooch with sapphire cabochon set in an onyx frame with rubies set in gold. The material on which the gems are mounted is not identified [Ref 1].

Figure 2. Art Deco sapphire and diamond inlayed silver cigarette case [Ref 2].

Figure 3. Art Deco diamond and sapphire ring [Ref 3].

Figure 4. Cuff links with ruby cabochon and sapphire set in white gold with black onyx trimmed stud [Ref 4].

Figure 5. Art Deco diamond, sapphire, and platinum watch [Ref 5].

Figure 6. Art Deco tiara with diamonds and sapphires set in white gold [Ref 6].

Figure 7. Art Deco diamond and sapphire bracelet, circa 1920 [Ref 7].

Figure 8. Art Deco brooch in Egyptian style set with sapphires, emeralds, and diamonds [Ref 8].

Figure 9. Diamond brooch set with sapphire accents [Ref 9].

Figure 10. Art Deco watch with cameos, set with sapphires and diamonds [Ref 10].

REFERENCES

Ref 1. http://www.doitjewelry.com/02/21/a-beautiful-and-rare-art-deco-brooch-french-circa-1930-centring-a-round-sapphire-cabochon-within-an-onyx-frame-and-further-set-with-calibre-rubies-mounted-in-gold-illegible-makers-mark-6-x-3c-3/

Ref 2. https://www.rubylane.com/item/821070-RT-4365/Art-Deco-Diamond-Sapphire-800-Silver

Ref 3. http://www.antiquejewel.com/en/2ndpage.asp?dtn=15033-0048

Ref 4. https://www.pinterest.com/pin/383861568224232322/

Ref 5. http://www.macklowegallery.com/search-antiques.asp/currentPage/-1/art-nouveau-antique-estate/art%20deco

Ref 6. https://www.pinterest.com/pin/368732288212254566/

Ref 7. https://www.langantiques.com/university/Art_Deco_Era_Jewelry

Ref 8. http://www.gemscene.com/art-deco.html

Ref 9. https://www.google.com/search?hl=en&biw=1180&bih=952&tbm=isch&sa=1&ei=4SMEXPngL4LMjgSM7IKgBA&q=sapphire+jewelry+and+art+made+in+art+deco+era&oq=sapphire+jewelry+and+art+made+in+art+deco+era&gs_l=img.12…8687.29358..31068…3.0..0.98.2380.32……0….1..gws-wiz-img.cb574UrAC_k#imgrc=ROK8ATGFQOWIgM:

Ref 10. http://www.antiquejewel.com/en/2ndpage.asp?dtn=13119-0030

Largest Star Sapphire/Ruby

Mineral Man Mel — Sun, 26 Jan 2020 17:16:52 +0000

We usually think of star sapphires and rubies as stones in the few carat range, not in hundreds and thousands of carats. But some are an amazing size. At the top, are the World’s Largest which are truly awesome. In this blog I’ll describe the worlds largest blue star sapphire, star ruby, and black star sapphire, as well as gems ranking near their size but just below the record. I’ll also include a short history of each gem.

Worlds Largest Blue Star Sapphire: The Star of Adam [Ref 1, Ref 2]

The world’s largest star sapphire weighs an amazing 1,4O4 carats, and when held, largely occupies the palm of a hand, as shown in Figure 1.

Figure 1. Star of Adam

The stone was found in the fall of 2015 at mine in the famed alluvial gem deposits near Ratnapura, Sri Lanka [Ref 1 Ref 2]. At first sight, the owner estimated the value of the gem at $175 million. As of January 2016, the owner was pondering whether to auction the gem or to display it. A diligent trip over the internet disclosed no further information about any attempt to auction the gem. However, the gem may have been sold in a private transaction.

World’s Largest Black Star Sapphire: The Black Star of Queensland [Ref 3, Ref 4, Ref 5]

The Black Star of Queensland, as shown in Figure 2, weighs 733 carats, and was the world’s largest sapphire until being displaced by the Star of Adam. This gem is also seen to fill the palm of a hand but does not have the cabochon height of the Star of Adam.

Reportedly, the rough stone was found by a twelve-year old boy, Roy Spencer, in the mid-1930s, in the Reward Claim near Anakie, Queensland, Australia [Ref 3]. The boy’s father, Harry Spencer, assumed it was merely a black crystal and the family used it as a doorstop for over a decade. A second look disclosed the gem.

The stone was sold by Spencer in 1947 to the jeweler Harry Kazanjian for $18,000AU which funded a new house for the family. The subsequent history of the stone has been shared by owners and institutions. The gem was loaned to the Natural History Museum of the Smithsonian Institution in 1969. In 1971 it was seen around Cher’s on television show. To fulfill a childhood dream, the artist and jeweler, Jack Armstrong, and his wealthy girlfriend, Gabrielle Grohe, convinced the Kazanjian family to sell the gem in 2003 [Ref 4]. In 2010 [Ref 5], the pair squabbled over the stone and Armstrong agreed to pay $500,000 for Grohe’s share, but failed to pay, and due to a judge’s ruling he lost all right to the gemstone.

Figure 2. Worlds largest black star sapphire [Ref 6].

World’ Largest Star Ruby: the Appalachian Ruby Star [Ref 7]

The Appalachian Ruby Star weighs 139.43 carats and barely edges out the Rosser Reeves Star ruby, that weighs in at 138.72 carats, as shown in Figure 3. The Appalachian Star ruby was cut from a rough ruby, which also yielded three additional stones. The weight of the group of four star rubies became known as the Mountain Star Ruby Collection and is shown in Figure 4. The aggregate weight of the rubies totals 342 carats.

The rough ruby was found in 1990 by Wayne Messer, a fishing guide in Western North Carolina. He had noted traces of corundum in a stream bed and traced the alluvial stones back to their source. Upon digging some eight feet, found the rough ruby. The quartet of star rubies was cut by Sam Fore from the rough stone which weighed 377 carats.

The Appalachian Star ruby was exhibited in 1992 at the Natural history Museum in London, drawing an estimated 150,000 people. Several attempts were made over the years to sell the collection, appraised at a value close to $100 million. Only recently, following the death of Messer, was the collection offered for sale.

Figure 3. The Appalachian Star, World’s Largest Star ruby [Ref 7].

Figure 4. The four star rubies, cut from the large rough ruby which gave the Appalachian Star [Ref 7].

The Rosser Reeves Ruby [Ref 8, Ref 9]

At a weight of 138.7 carats, the Rosser Reeve Ruby is the world’s second heaviest star ruby, and was found in Sri Lanka. The gem is named after Rosser Reeves a pioneer in the advertising industry. Rosser donated the gem to the Smithsonian Institute in 1965. Despite his attractive tale of buying the gem at an auction in Istanbul, he actually bought the gem from Robert C. Nelson Jr. At purchase, the stone weighed just over 140 carats, but was scratched and so was re-polished, which also helped to re-center the star on the Cabochon. Fortunately for museum goers, this beautiful gem still can be seen at the Smithsonian institute. As a note, the Wikipedia article used as the reference for this segment of the blog was written by Brendan Reeves, great grandson of Rosser.

Figure 5. The Rosser Reeves star ruby [Ref 9].

REFERENCES

Ref 1. https://www.forbes.com/sites/trevornace/2016/01/10/worlds-largest-blue-star-sapphire-found-worth-300-million/#6a06d4f075d1

Ref 2. https://www.mindat.org/loc-3147.html

Ref 3. https://en.wikipedia.org/wiki/Black_Star_of_Queensland#cite_note-5

Ref 4. https://www.upi.com/Feature-Legendary-sapphire-for-sale/10481044491153/

Ref 5. http://articles.latimes.com/2010/jan/05/local/la-me-blacksapphire5-2010jan05/2

Ref 6. https://www.pinterest.com/pin/863987509737025682/

Ref 7. https://www.mnn.com/earth-matters/wilderness-resources/blogs/extremely-rare-star-rubies-found-fishing-guide-could-fetch-millions

Ref 8. https://en.wikipedia.org/wiki/Rosser_Reeves_Ruby

Ref 9. https://geogallery.si.edu/10002811/rosser-reeves-star-ruby

Corundum – From Sapphires to Rubies

Mineral Man Mel — Sun, 10 Nov 2019 17:08:54 +0000

Gemstones of the mineral corundum [Ref 1] offer a rainbow of colors for the lapidarist and jewelry maker as displayed in Figure 1.

Traditionally, of these, the ruby and blue sapphire, along with diamond and emerald, are considered to be the four-membered family of precious gems. Corundum gemstones, other than the ruby and blue sapphire, are also considered sapphires, having colors ranging from green to pink.

In this blog, I’ll describe the crystallography of corundum, and the physical and optical properties of corundum, including the sources of the colors in its gemstones. I will also present a gallery of ruby and sapphire mineral specimens.

Figure 1. A rainbow of the gemstones from corundum: ruby, blue sapphire, and green to pink sapphires.

CRYSTALLOGRAPHY OF CORUNDUM [Ref 1]

Crystal System of Corundum

Corundum crystallizes in the Trigonal System, which has three axes in a plane and are arranged at 120 degrees to each other, with an axis perpendicular to the plane, as shown in Figure 2. Of the typical forms of crystals shown in the figure, corundum frequently crystallizes as a hexagonal prism, terminated by the basal pinacoid; as a bipyramid, the hexagonal prism is terminated by a bipyramid; the rhombehedron and the hexagonal prism are terminated by the rhombehedron, and the schalenohedron. Examples of corundum crystals taking these forms are shown in Figures 5-11. Figure 7 shows a diagram of a crystal exhibiting all of these forms except the rhombohedron and schalenohedron. The latter form is shown by the sapphire crystal in Figure 10.

Figure 2. The four axes of the trigonal crystal system

Figure 3. Properties of the Trigonal Crystal System

Figure 4. Crystal of corundum with typical forms; only the schalenohedron is not shown.

Twinning in Corundum [Ref 1].

Multiple twinning on the rhombohedral plane with laminar structure with striations on both the basal pinacoid perpendicular to the c-axis and the hexagonal prism or on bipyramid faces, as shown by the terminated bipyrimidal sapphire crystal, shown in Figure 10 [Ref 12]. Corundum is also twinned on the hexagonal prism faces of tabular crystals exhibiting an arrowhead shape, as shown by the sapphire specimen in Figure 11[Ref 13]. The view is at the base of the arrowhead shape and pointing towards the tip. Less frequent twinning in corundum occurs on the basal pinacoid, perpendicular to the long axis of the crystal, as showing repetitive twinning along its length in Figure 12.

The view is at the base of the arrowhead shape and pointing towards the tip. Less frequent twinning in corundum occurs on the basal pinacoid, perpendicular to the long axis of the crystal, as showing repetitive twinning along its length in Figure 12.

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MECHANICAL PROPERTIES OF CORUNDUM [Ref 2]

The high values of hardness and ultimate strength and its resistance to cleavage, underlie the toughness of corundum gemstones and their wide usage in rings and bracelets, both susceptible to impact while worn. Values of the strength factors of corundum are summarized in TABLE I.

TABLE I. STRENGTH FACTORS OF CORUNDUM GEMSTONES

PROPERTY	VALUE/OBSERVATION	REFERENCE
Mohs Hardness SCALE	9 (Member of scale)	11
Ultimate Compressive Strength	435,000 psi	13
Ultimate Tensile Strength	43,500 psi	13
Flexural Strength	58, 000	13
Tenacity	Brittle	11
Fracture	Irregular/Uneven, Conchoidal	11
Cleavage	None Observed	11

OPTICAL PROPERTIES OF CORUNDUM [Ref 1]

The Refractive Index values of corundum lie in the ranges 1.759-1.772 depending on direction of light polarization. These values are considerably below the value of 2.418 for diamond [Ref 3], and underlies the beauty of corundum gemstones being in their vivid colors and not in brilliance or fire.

The light reflected from the surface, without penetration into gemstones is colorless, as often seen in photographs of gemstones, as in Figure 14.

Light scattering from oriented needle-like crystals of rutile, or to colloidal or other material in oriented tubules is observed in the star sapphire and star ruby as described in another blog on star rubies and sapphires [Ref 4].

Figure 14. Reflections from the surface of the ruby gemstone are colorless, while those reflected from the back of the stone are colored.

SOURCES OF COLOR IN CORUNDUM GEMSTONES

Corundum is aluminum oxide, with the formula Al₂O_3. Each trivalent aluminum Al³⁺ion is surrounded by six oxygen ions, located at the tips of an octahedron in the crystal lattice of corundum, shown in Figure 15. Defects in the forms of ions of metal impurities substituting for the aluminum ion, are responsible for the colors of corundum [Ref 5 ]. The impurity metal ions and the associated colors are summarized in Table I, shown in Figure 4. The divalent and trivalent ions substitute for the aluminum ion in the lattice of the corundum lattice.

Figure 15. Crystal lattice of corundum.

Figure 4. Sources of colors in corundum gemstones. See legend for terms below.

Legend for Figure 4
Cr³⁺ = Trivalent chromium ion
Fe³⁺ = Trivalent iron ion
Fe²⁺ = Divalent iron ion
Ti⁴⁺ = Tetravalent titanium ion
O¹-V = neighboring monovalent oxygen ion O^1- and lattice vacancy V in lattice
taking the place of an Al³⁺ ion.
Al³⁺ = Trivalent aluminum ion

COLOR CHANGES IN HEAT TREATED SAPPHIRES

Consideration of the various colors in natural sapphires, having different combinations and concentrations of the ions and ion pairs, before and after their heat treatment, serves to demonstrate their effects on color in corundum gemstones. The results of heat treatments are shown in Figures 16-18.

Some sapphires are heat treated to improve the attractiveness of their colors. Studies were carried out to identify changes in concentrations of ions that led to improvements in the aesthetics of the gem stone. The studies showed two major effects in the brown-toned sapphires and in the optical absorption spectrum of sample rO 4/5, red orange. The red trace of the absorption spectrum shows increased absorption due to the chromium ion, a decreased absorption due to trivalent iron ion pairs contributed from paired divalent and trivalent iron ions and single trivalent iron ions. The heat treatment resulted in an increased number of paired divalent iron ions and tetravalent titanium ions. The lessened absorption by iron ions resulted in smaller contributions to the color of the gemstone in the yellow to orange spectral range. Increased trivalent chromium ion concentration resulted in increased absorption of the blue and yellow spectral range and increased transmission in the red spectral range. Increased absorption in the yellow-orange range, due to increased absorption by paired divalent iron and tetravalent titanium ions resulted in increased transmission in the blue spectral range. The lessened transmission in the yellow-orange and increase transmission in the red and blue color ranges resulted in the cherry-pink color of the gemstone.

Figure 16. Ranges of colors in sapphires obtained with heat treatment under reducing conditions, within two temperature ranges.

Figure 17. Samples of sapphires before and after heat treatments at 1100-1700
Degrees C. Samples before treatment are shown in the top row and after treatment shown in the following rows.

Figure 18. Changes in light absorption and transmission in a sapphire with a red-orange color before treatment and a cherry-pink color achieved after treatment.

GALLERY OF SAPPHIRE AND RUBY SPECIMENS

Many specimens on display are from alluvial deposits where erosion of the edges and faces arose from wear against surrounding gravel and sand.

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Ref 1. https://www.mindat.org/min-1136.html

Ref 2. http://www.matweb.com/search/datasheet_print.aspx?matguid=c8c56ad547ae4cfabad15977bfb537f1

Ref 3.

https://refractiveindex.info/?shelf=3d&book=crystals&page=diamond

Ref 4. https://en.wikipedia.org/wiki/Asterism_(gemology)

Ref 5.

https://www.researchgate.net/publication/273531857_The_Color_Change_of_Natural_Green_Sapphires_by_Heat_Treatment/download

Ref 6.

https://www.degruyter.com/downloadpdf/j/adms.2012.12.issue-2/v10077-012-0006-3/v10077-012-0006-3.pdf