Ruby and Sapphire Grading Tools

GEMOLOGY

names were rst converted into Munsell color codes, and then Ruby And Sapphire Grading Tools modi ed so that they can be better understood by relying on the color code charts of the By Thanong Leelawatanasuk, Wilawan Atichat, Visut Pisutha-Arnond and Pornsawat Wathanakul; GIT ISCC-NBS (Inter-Society Color Council-National Bureau of Standards) system. Quality factors of ruby and hen someone wants to might be priced lower if the seller is higher than blue sapphire, and blue sapphire were determined by buy a gemstone or piece in need of money. Thus prices do not sapphire is typically of higher clarity polling gem dealers and of gem-set jewelry, necessarily reect quality. than ruby. Hence, clarity defects in gemologists, both at GIT and at common questions include: That said, the gem trade has long ruby have less of an impact on international gem shows. The used certain criteria for evaluating price than the same defects in resulting data was then used as a • Is it a genuine stone? quality. In order to re ne these blue sapphire. foundation to establish the eight • Has it undergone any criteria to improve consumer GIT's quality assessment system primary sets of master stones. con dence, the Gem and Jewelry for gem corundum has been treatments? Color grading methodology is as Institute of Thailand (GIT) has developed and continually follows. Stones must be placed Notable Colors: Pigeon’s to by ill-de ned terms such as white pigeon. The famous British • What is its quality? conducted in-depth research on the re ned through consultations Blood and Royal Blue pigeon's blood red, royal blue and gemologist, J.F. Halford-Watkins, • Is the price fair? subject, speci cally on gem with both gem traders and Among the 4 C's factors, color has cornower blue. who lived many years in Mogok, corundum varieties. The objective is gemologists (Janthayot et al., 2001, the greatest impact on price, "Pigeon's blood" (ko-twe in described it as a rich crimson Proper answers to such questions to create standards that provide an 2003a, 2003b, 2003c, 2004, 2007; particularly at the high end of the Burmese) has been variously without any trace of blue overtones are crucial for creating consumer accurate, reliable measure for Siripant 1999; Siripant et al., 2001 price scale. compared to drops of blood from (Hughes, 1997). con dence. This article addresses colored stones’ quality. and 2003). The institute has In former times, the nest colors the nose of a freshly-slain pigeon, Typical terms for sapphire include one of those questions, that of established colored stone master of ruby and sapphire were referred to the color of the eye of a "royal blue" and "cornower blue". de ning quality. Methodology sets for eight varieties of gem The prices of gems do not always Both diamonds and colored stones corundum, i.e., ruby, blue sapphire, reect the underlying quality are traditionally graded according to padparadscha, yellow sapphire, because prices are inuenced by four important quality factors (4Cs): pink sapphire, purple sapphire, many factors completely apart from Color, Clarity, Cut and Carat Weight. orange sapphire and green objective quality. For example, a But the impact of each factor on sapphire. All master stones are oval piece might be priced high if it was pricing differs from one variety to shaped and of at least 0.50 ct each. bought at a time when the market another. For example, the clarity of GIT’s standards are based on the price was higher; similarly a gem yellow sapphire is, on the average, Munsell system. Common Thai color

25 cm from the standard light source, which consists of a Gretag Macbeth 5000° Kelvin lamp with an intensity of 1200 lux). This lamp is designed to simulate north daylight. Stones are visually graded in the face-up position at a distance of 30 cm. Hue, tone, and saturation of the stones are considered; dispersion and scintillation are excluded. Overall stone quality was also taken into account, with stones chosen to be used in the standard The three most famous varieties of gem corundum: ruby, blue sapphire and yellow sapphire. Photos: Wimon Manorotkul (left and center) and sets needing to be similar in clarity, Vlad Yavorskyy (right) size and cutting style.

46 InColor Spring 2014 www.gemstone.org

Corundum Color Master master set comprises eight master help consumer con dence. Sets: Pigeon’s Blood Ruby stones in a range of vivid red or blue and Royal Blue Sapphire with intense color and medium to Other Master Sets Because of the ambiguity of these dark tone. GIT has also conducted research on color terms, GIT set out to create These master stone sets for clarity and cut grading standards for master sets to de ne them “Pigeon’s Blood” and “Royal Blue” ruby and blue sapphire. (Janthayot et al., 2001, 2003a and colors illustrate, and identify "Cut” is de ned by a gemstone’s 2007). These master sets were common colors used in the gem proportions and nish. Proportion created by consultations with both trade. By standardizing such color refers to the dimensions and overall gem dealers and gemologists. Each de nitions, it is hoped that this will symmetry of a gemstone, while nish

describes the precision and Janthayot, P ., Sae-Joo, S., Kaewmanee, S. and neatness of the facets and polishing Singbamroong, S. (2003c) Cut Grading System of Acknowledgements quality. Symmetrical face-up and Corundum. The Gem and Jewelry Institute of GIT would like to thank all of the gem traders, pro le symmetry, combined with Thailand (Public Organization) Bangkok, Thailand, experts and researchers who have contributed to crown-to-pavilion proportion rations 101 p. (In Thai) this project. of about 1:3 to 1:4 leads to higher Janthayot, P., Khunwisutthiphan, C., Sae-Joo, S and cutting grades. Singbamroong, S . (2004) Quality Assessment Unfortunately, due to very high Standard of Gem Corundum. The Gem and Jewelry value of such stones, cutters are Institute of Thailand (Public Organization) Bangkok, forced to maximize weight Thailand, 96 p. (In Thai) retention. Hence, very few stones References possess ideal proportions. Janthayot, P., Atichat, W., Suriyachod, C., Sakrapee Clarity is another factor that Hughes R.W. (1997) Ruby and Sapphire. RWH S. and Saengbuangarmlum, S. (2007) The inuences the value of ruby and publishing, 512 p. Improvement of Gem Corundum Color sapphire. Clarity is determined Hughes R.W. (2014). Ruby & Sapphire: A Collectors’ Communication System. The Gem and Jewelry based on the size, number, position, Guide. The Gem and Jewelry Institute of Thailand, Institute of Thailand (Public Organization) Bangkok, color and nature of inclusions. Ruby 384 p. Thailand, 105 p. (In Thai) is rarely loupe-clean or even Janthayot, P., Kankaew, Y. and Singbamroong, S. Siripant, S. (1999) A Gem Color Communication eye-clean. In contrast, sapphire (2001) Color Grading System of Ruby. The Gem and System. The Thailand Research Fund. 86 p. (In Thai) generally features fewer inclusions, Jewelry Institute of Thailand (Public Organization) and thus loupe-clean or eye-clean Siripant, S., Janthayot, P., Kankaew, Y,. and Bangkok, Thailand, 58 p. (In Thai) stones are the standard in the trade. Singbamroong, S. (2001) A Gem Color Janthayot, P ., Sae-Joo, S., Kaewmanee, S. and Communication System (Ruby). The Gem and Singbamroong, S. (2003a) Color Grading System of Jewelry Institute of Thailand (Public Organization) Conclusion Bangkok, Thailand, 58 p. (In Thai) GIT’s ruby and sapphire quality Blue Sapphire and other Sapphires. The Gem and evaluation system is intended to be Jewelry Institute of Thailand (Public Organization) Siripant, S., Janthayot, P., Sae-Joo, S., Kaewmanee, used as a general standard in the Bangkok, Thailand, 200 p. (In Thai) S. and Singbamroong, S. (2003) Quality Standard of gem and jewelry industry. The Janthayot, P ., Sae-Joo, S., Kaewmanee, S. and Blue and Other Sapphire. The Gem and Jewelry ultimate goal is to use these Singbamroong, S. (2003b) Clarity Grading System Institute of Thailand (Public Organization) Bangkok, standards as tools for promoting the of Corundum. The Gem and Jewelry Institute of Thailand, 200 p. (In Thai) colored stone trade and building Thailand (Public Organization) Bangkok, Thailand, consumer con dence. 67 p. (In Thai) names were rst converted into Munsell color codes, and then modi ed so that they can be better understood by relying on the color code charts of the ISCC-NBS (Inter-Society Color Council-National Bureau of Standards) system. Quality factors of ruby and hen someone wants to might be priced lower if the seller is higher than blue sapphire, and blue sapphire were determined by buy a gemstone or piece in need of money. Thus prices do not sapphire is typically of higher clarity polling gem dealers and of gem-set jewelry, necessarily reect quality. than ruby. Hence, clarity defects in gemologists, both at GIT and at common questions include: That said, the gem trade has long ruby have less of an impact on international gem shows. The used certain criteria for evaluating price than the same defects in resulting data was then used as a • Is it a genuine stone? quality. In order to re ne these blue sapphire. foundation to establish the eight • Has it undergone any criteria to improve consumer GIT's quality assessment system primary sets of master stones. con dence, the Gem and Jewelry for gem corundum has been treatments? Color grading methodology is as Institute of Thailand (GIT) has developed and continually follows. Stones must be placed Notable Colors: Pigeon’s to by ill-de ned terms such as white pigeon. The famous British • What is its quality? conducted in-depth research on the re ned through consultations Blood and Royal Blue pigeon's blood red, royal blue and gemologist, J.F. Halford-Watkins, • Is the price fair? subject, speci cally on gem with both gem traders and Among the 4 C's factors, color has cornower blue. who lived many years in Mogok, corundum varieties. The objective is gemologists (Janthayot et al., 2001, the greatest impact on price, "Pigeon's blood" (ko-twe in described it as a rich crimson Proper answers to such questions to create standards that provide an 2003a, 2003b, 2003c, 2004, 2007; particularly at the high end of the Burmese) has been variously without any trace of blue overtones are crucial for creating consumer accurate, reliable measure for Siripant 1999; Siripant et al., 2001 price scale. compared to drops of blood from (Hughes, 1997). con dence. This article addresses colored stones’ quality. and 2003). The institute has In former times, the nest colors the nose of a freshly-slain pigeon, Typical terms for sapphire include one of those questions, that of established colored stone master of ruby and sapphire were referred to the color of the eye of a "royal blue" and "cornower blue". de ning quality. Methodology sets for eight varieties of gem The prices of gems do not always Both diamonds and colored stones corundum, i.e., ruby, blue sapphire, reect the underlying quality are traditionally graded according to padparadscha, yellow sapphire, because prices are inuenced by four important quality factors (4Cs): pink sapphire, purple sapphire, many factors completely apart from Color, Clarity, Cut and Carat Weight. orange sapphire and green objective quality. For example, a But the impact of each factor on sapphire. All master stones are oval piece might be priced high if it was pricing differs from one variety to shaped and of at least 0.50 ct each. bought at a time when the market another. For example, the clarity of GIT’s standards are based on the price was higher; similarly a gem yellow sapphire is, on the average, Munsell system. Common Thai color

25 cm from the standard light source, which consists of a Gretag Macbeth 5000° Kelvin lamp with an intensity of 1200 lux). This lamp is designed to simulate north daylight. Stones are visually graded in the face-up position at a distance of 30 cm. Hue, tone, and saturation of the stones are considered; dispersion and scintillation are excluded. Overall stone quality was also taken into account, with stones chosen to be used in the standard sets needing to be similar in clarity, Examples of the primary masters that have been prepared, based on the Munsell color communication system. (Photos: GIT) size and cutting style.

www.gemstone.org InColor Spring 2014 47

names were rst converted into Munsell color codes, and then modi ed so that they can be better understood by relying on the color code charts of the ISCC-NBS (Inter-Society Color Council-National Bureau of Standards) system. Quality factors of ruby and hen someone wants to might be priced lower if the seller is higher than blue sapphire, and blue sapphire were determined by buy a gemstone or piece in need of money. Thus prices do not sapphire is typically of higher clarity polling gem dealers and of gem-set jewelry, necessarily reect quality. than ruby. Hence, clarity defects in gemologists, both at GIT and at common questions include: That said, the gem trade has long ruby have less of an impact on international gem shows. The used certain criteria for evaluating price than the same defects in resulting data was then used as a • Is it a genuine stone? quality. In order to re ne these blue sapphire. foundation to establish the eight • Has it undergone any criteria to improve consumer GIT's quality assessment system primary sets of master stones. con dence, the Gem and Jewelry for gem corundum has been treatments? Color grading methodology is as Institute of Thailand (GIT) has developed and continually follows. Stones must be placed Notable Colors: Pigeon’s to by ill-de ned terms such as white pigeon. The famous British • What is its quality? conducted in-depth research on the re ned through consultations Blood and Royal Blue pigeon's blood red, royal blue and gemologist, J.F. Halford-Watkins, • Is the price fair? subject, speci cally on gem with both gem traders and Among the 4 C's factors, color has cornower blue. who lived many years in Mogok, corundum varieties. The objective is gemologists (Janthayot et al., 2001, the greatest impact on price, "Pigeon's blood" (ko-twe in described it as a rich crimson Proper answers to such questions to create standards that provide an 2003a, 2003b, 2003c, 2004, 2007; particularly at the high end of the Burmese) has been variously without any trace of blue overtones are crucial for creating consumer accurate, reliable measure for Siripant 1999; Siripant et al., 2001 price scale. compared to drops of blood from (Hughes, 1997). con dence. This article addresses colored stones’ quality. and 2003). The institute has In former times, the nest colors the nose of a freshly-slain pigeon, Typical terms for sapphire include one of those questions, that of established colored stone master of ruby and sapphire were referred to the color of the eye of a "royal blue" and "cornower blue". de ning quality. Methodology sets for eight varieties of gem The prices of gems do not always Both diamonds and colored stones corundum, i.e., ruby, blue sapphire, reect the underlying quality are traditionally graded according to padparadscha, yellow sapphire, because prices are inuenced by four important quality factors (4Cs): pink sapphire, purple sapphire, many factors completely apart from Color, Clarity, Cut and Carat Weight. orange sapphire and green objective quality. For example, a But the impact of each factor on sapphire. All master stones are oval piece might be priced high if it was pricing differs from one variety to shaped and of at least 0.50 ct each. bought at a time when the market another. For example, the clarity of GIT’s standards are based on the price was higher; similarly a gem yellow sapphire is, on the average, Munsell system. Common Thai color

25 cm from the standard light source, which consists of a Gretag Macbeth 5000° Kelvin lamp with an intensity of 1200 lux). This lamp is designed to simulate north daylight. Stones are visually graded in the face-up position at a distance of 30 cm. Hue, tone, and saturation of the stones are considered; dispersion and scintillation are excluded. Overall stone quality was also taken into account, with stones chosen to be used in the standard sets needing to be similar in clarity, size and cutting style. GIT’s master sets of ruby and blue sapphire. (Photos: GIT)

48 InColor Spring 2014 www.gemstone.org

describes the precision and Janthayot, P ., Sae-Joo, S., Kaewmanee, S. and neatness of the facets and polishing Singbamroong, S. (2003c) Cut Grading System of Acknowledgements quality. Symmetrical face-up and Corundum. The Gem and Jewelry Institute of GIT would like to thank all of the gem traders, pro le symmetry, combined with Thailand (Public Organization) Bangkok, Thailand, experts and researchers who have contributed to crown-to-pavilion proportion rations 101 p. (In Thai) this project. of about 1:3 to 1:4 leads to higher Janthayot, P., Khunwisutthiphan, C., Sae-Joo, S and cutting grades. Singbamroong, S . (2004) Quality Assessment Unfortunately, due to very high Standard of Gem Corundum. The Gem and Jewelry value of such stones, cutters are Institute of Thailand (Public Organization) Bangkok, forced to maximize weight Thailand, 96 p. (In Thai) retention. Hence, very few stones References possess ideal proportions. Janthayot, P., Atichat, W., Suriyachod, C., Sakrapee Clarity is another factor that Hughes R.W. (1997) Ruby and Sapphire. RWH S. and Saengbuangarmlum, S. (2007) The inuences the value of ruby and publishing, 512 p. Improvement of Gem Corundum Color sapphire. Clarity is determined Hughes R.W. (2014). Ruby & Sapphire: A Collectors’ Communication System. The Gem and Jewelry based on the size, number, position, Guide. The Gem and Jewelry Institute of Thailand, Institute of Thailand (Public Organization) Bangkok, color and nature of inclusions. Ruby 384 p. Thailand, 105 p. (In Thai) is rarely loupe-clean or even Janthayot, P., Kankaew, Y. and Singbamroong, S. Siripant, S. (1999) A Gem Color Communication eye-clean. In contrast, sapphire (2001) Color Grading System of Ruby. The Gem and System. The Thailand Research Fund. 86 p. (In Thai) generally features fewer inclusions, Jewelry Institute of Thailand (Public Organization) and thus loupe-clean or eye-clean Siripant, S., Janthayot, P., Kankaew, Y,. and Bangkok, Thailand, 58 p. (In Thai) stones are the standard in the trade. Singbamroong, S. (2001) A Gem Color Janthayot, P ., Sae-Joo, S., Kaewmanee, S. and Communication System (Ruby). The Gem and Singbamroong, S. (2003a) Color Grading System of Jewelry Institute of Thailand (Public Organization) Conclusion Bangkok, Thailand, 58 p. (In Thai) GIT’s ruby and sapphire quality Blue Sapphire and other Sapphires. The Gem and evaluation system is intended to be Jewelry Institute of Thailand (Public Organization) Siripant, S., Janthayot, P., Sae-Joo, S., Kaewmanee, used as a general standard in the Bangkok, Thailand, 200 p. (In Thai) S. and Singbamroong, S. (2003) Quality Standard of gem and jewelry industry. The Janthayot, P ., Sae-Joo, S., Kaewmanee, S. and Blue and Other Sapphire. The Gem and Jewelry ultimate goal is to use these Singbamroong, S. (2003b) Clarity Grading System Institute of Thailand (Public Organization) Bangkok, standards as tools for promoting the of Corundum. The Gem and Jewelry Institute of Thailand, 200 p. (In Thai) colored stone trade and building Thailand (Public Organization) Bangkok, Thailand, consumer con dence. 67 p. (In Thai) names were rst converted into Munsell color codes, and then modi ed so that they can be better understood by relying on the color code charts of the ISCC-NBS (Inter-Society Color Council-National Bureau of Standards) system. Quality factors of ruby and hen someone wants to might be priced lower if the seller is higher than blue sapphire, and blue sapphire were determined by buy a gemstone or piece in need of money. Thus prices do not sapphire is typically of higher clarity polling gem dealers and of gem-set jewelry, necessarily reect quality. than ruby. Hence, clarity defects in gemologists, both at GIT and at common questions include: That said, the gem trade has long ruby have less of an impact on international gem shows. The used certain criteria for evaluating price than the same defects in resulting data was then used as a • Is it a genuine stone? quality. In order to re ne these blue sapphire. foundation to establish the eight Top quality samples of ruby (left) and blue sapphire (right). (Photos: Wimon Manorotkul) • Has it undergone any criteria to improve consumer GIT's quality assessment system primary sets of master stones. con dence, the Gem and Jewelry for gem corundum has been treatments? Color grading methodology is as Institute of Thailand (GIT) has developed and continually follows. Stones must be placed Notable Colors: Pigeon’s to by ill-de ned terms such as white pigeon. The famous British • What is its quality? conducted in-depth research on the re ned through consultations Blood and Royal Blue pigeon's blood red, royal blue and gemologist, J.F. Halford-Watkins, • Is the price fair? subject, speci cally on gem with both gem traders and Among the 4 C's factors, color has cornower blue. who lived many years in Mogok, corundum varieties. The objective is gemologists (Janthayot et al., 2001, the greatest impact on price, "Pigeon's blood" (ko-twe in described it as a rich crimson Proper answers to such questions to create standards that provide an 2003a, 2003b, 2003c, 2004, 2007; particularly at the high end of the Burmese) has been variously without any trace of blue overtones are crucial for creating consumer accurate, reliable measure for Siripant 1999; Siripant et al., 2001 price scale. compared to drops of blood from (Hughes, 1997). con dence. This article addresses colored stones’ quality. and 2003). The institute has In former times, the nest colors the nose of a freshly-slain pigeon, Typical terms for sapphire include one of those questions, that of established colored stone master of ruby and sapphire were referred to the color of the eye of a "royal blue" and "cornower blue". de ning quality. Methodology sets for eight varieties of gem The prices of gems do not always Both diamonds and colored stones corundum, i.e., ruby, blue sapphire, reect the underlying quality are traditionally graded according to padparadscha, yellow sapphire, because prices are inuenced by four important quality factors (4Cs): pink sapphire, purple sapphire, many factors completely apart from Color, Clarity, Cut and Carat Weight. orange sapphire and green objective quality. For example, a But the impact of each factor on sapphire. All master stones are oval piece might be priced high if it was pricing differs from one variety to shaped and of at least 0.50 ct each. bought at a time when the market another. For example, the clarity of GIT’s standards are based on the price was higher; similarly a gem yellow sapphire is, on the average, Munsell system. Common Thai color

25 cm from the standard light source, which consists of a Gretag Macbeth 5000° Kelvin lamp with an intensity of 1200 lux). This lamp is designed to simulate north daylight. Stones are visually graded in the face-up position at a distance of 30 cm. Hue, tone, and saturation of the stones are considered; dispersion and scintillation are excluded. Overall stone quality was also taken into account, with stones chosen to be used in the standard sets needing to be similar in clarity, size and cutting style. Examples of well cut natural rubies and blue sapphires selected for master stones. (Photos: Jirapit Jakkrawanvibul)

www.gemstone.org InColor Spring 2014 49

25 cm from the standard light source, which consists of a Gretag Macbeth 5000° Kelvin lamp with an intensity of 1200 lux). This lamp is designed to simulate north daylight. Stones are visually graded in the face-up position at a distance of 30 cm. Hue, tone, and saturation of the stones are considered; dispersion and scintillation are excluded. Overall stone quality was also taken into account, with stones chosen to be used in the standard sets needing to be similar in clarity, size and cutting style.

GEMOLOGY

Too dark

50 InColor Spring 2014 www.gemstone.org names were rst converted into Munsell color codes, and then modi ed so that they can be better understood by relying on the color code charts of the ISCC-NBS (Inter-Society Color Council-National Bureau of Standards) system. Quality factors of ruby and hen someone wants to might be priced lower if the seller is higher than blue sapphire, and blue sapphire were determined by buy a gemstone or piece in need of money. Thus prices do not sapphire is typically of higher clarity polling gem dealers and of gem-set jewelry, necessarily reect quality. than ruby. Hence, clarity defects in gemologists, both at GIT and at common questions include: That said, the gem trade has long ruby have less of an impact on international gem shows. The used certain criteria for evaluating price than the same defects in resulting data was then used as a • Is it a genuine stone? quality. In order to re ne these blue sapphire. foundation to establish the eight • Has it undergone any criteria to improve consumer GIT's quality assessment system primary sets of master stones. con dence, the Gem and Jewelry for gem corundum has been treatments? Color grading methodology is as Institute of Thailand (GIT) has developed and continually follows. Stones must be placed Notable Colors: Pigeon’s to by ill-de ned terms such as white pigeon. The famous British • What is its quality? conducted in-depth research on the re ned through consultations Blood and Royal Blue pigeon's blood red, royal blue and gemologist, J.F. Halford-Watkins, • Is the price fair? subject, speci cally on gem with both gem traders and Among the 4 C's factors, color has cornower blue. who lived many years in Mogok, corundum varieties. The objective is gemologists (Janthayot et al., 2001, the greatest impact on price, "Pigeon's blood" (ko-twe in described it as a rich crimson Proper answers to such questions to create standards that provide an 2003a, 2003b, 2003c, 2004, 2007; particularly at the high end of the Burmese) has been variously without any trace of blue overtones are crucial for creating consumer accurate, reliable measure for Siripant 1999; Siripant et al., 2001 price scale. compared to drops of blood from (Hughes, 1997). con dence. This article addresses colored stones’ quality. and 2003). The institute has In former times, the nest colors the nose of a freshly-slain pigeon, Typical terms for sapphire include one of those questions, that of established colored stone master of ruby and sapphire were referred to the color of the eye of a "royal blue" and "cornower blue". de ning quality. Methodology sets for eight varieties of gem The prices of gems do not always Both diamonds and colored stones corundum, i.e., ruby, blue sapphire, reect the underlying quality are traditionally graded according to padparadscha, yellow sapphire, because prices are inuenced by four important quality factors (4Cs): pink sapphire, purple sapphire, many factors completely apart from Color, Clarity, Cut and Carat Weight. orange sapphire and green objective quality. For example, a But the impact of each factor on sapphire. All master stones are oval piece might be priced high if it was pricing differs from one variety to shaped and of at least 0.50 ct each. bought at a time when the market another. For example, the clarity of GIT’s standards are based on the price was higher; similarly a gem yellow sapphire is, on the average, Munsell system. Common Thai color

25 cm from the standard light source, which consists of a Gretag Macbeth 5000° Kelvin lamp with an intensity of 1200 lux). This lamp is designed to simulate north daylight. Stones are visually graded in the face-up position at a distance of 30 cm. Hue, tone, and saturation of the stones are considered; dispersion and scintillation are excluded. Overall stone quality was also taken into account, with stones chosen to be used in the standard sets needing to be similar in clarity, size and cutting style.

Ratios of crown-to-pavilion pro le proportion in ruby. Proportion ratios of 1:3 to 1:4 enhance light return. (Photo: GIT)