New Guidelines to define Colour of White Gold
The White Gold Task Force, an initiative of the MJSA and the World Gold Council have launched a set of Guidelines to define the colour of White Gold at the MJSA’s EXPO New York show on Monday, 7th March 2005. This are voluntary USA Industry Guidelines that are expected to be widely adopted internationally (and which may lead to an ISO standard at a future date).
The lack of an industry-accepted definition of white as applied to white gold has been a problem
in the industry, where rhodium plating of white gold has become common, thus hiding the real colour of the white gold from the consumer at the time of purchase. Rhodium plating of white gold is legal in most countries. For good technical and economic reasons, the term ‘white’ has been used elastically to encompass a wide range of colour and this has led to consumer dissatisfaction.The technical issues surrounding white gold were discussed at a Round Table meeting at EXPO NY in March 2003 and this resulted in a consensus for action by the US industry participants.
A pair of earrings with the rhodium plating partially removed
to reveal the poor white colour of the white gold
The MJSA and World Gold Council took the initiative to set up the White Gold Task Force, with the main objective to define white as a colour in white golds. An issue has been to find a user-friendly procedure for the industry to determine the degree of whiteness of a particular piece of white gold jewellery.
The technical issues surrounding white gold were discussed at a Round Table meeting at EXPO NY in March 2003 and this resulted in a consensus for action by the US industry participants. The MJSA and World Gold Council took the initiative to set up the White Gold Task Force, with the main objective to define white as a colour in white golds. An issue has been to find a user-friendly procedure for the industry to determine the degree of whiteness of a particular piece of white gold jewellery.
Colour, of course, can be measured quantitatively in a reproducible way. The conditions of measurement, especially the incident lighting, are important. Generally a ‘Northern Daylight’ illumination is preferred. The degree of whiteness of a white gold can be described in terms of a numerical parameter called the ASTM Yellowness Index: 1925 and is calculated from the basic tri-stimulus values, X, Y & Z, measured with a colour spectrophotometer. The lower the value, the whiter is the gold. [For more information on this parameter, see the scientific article by Manchandra and Henderson in Gold Bulletin, volume 38 (2) which will be published in June 2005 on the website, www.goldbulletin.org]
The Guidelines: [1] Definition of White Gold
White gold has been defined as having a Yellowness Index value of 32.0 or less.
This is additionally limited in terms of CIELab co-ordinates as having an L value of at least 75, and an a* value between +3.0 and –3.5
Measurement conditions are:
Illuminant C (D65 is a close approximation), observer angle 2°, specular and ultraviolet components included. Samples polished to 6 micron finish.
Such measurements should be carried out in a light box with the correct lamp or at least under a lamp with a D65 illuminant. These are available through the MJSA or directly through Gretag MacBeth.
The Guidelines: [2] The Grades of White Gold
Within the definition of the colour of white gold , it is proposed that 3 grades of white gold are defined:
• GRADE 1 (Premium white grade) – these alloys have a good white colour and do not need rhodium plating.• GRADE 2 (Standard grade) – reasonable white colour; rhodium plating is optional for these alloys• GRADE 3 (Off-white colour) – such alloys need to be rhodium plated
Any alloys falling outside of these three grades are classed as non-white. In terms of the Yellowness Index, these grades can be defined as follows,
Table 2 Grades of white in white golds
Grade
Yellowness Index value
Grade 1 (Premium)
The technical issues surrounding white gold were discussed at a Round Table meeting at EXPO NY in March 2003 and this resulted in a consensus for action by the US industry participants. The MJSA and World Gold Council took the initiative to set up the White Gold Task Force, with the main objective to define white as a colour in white golds. An issue has been to find a user-friendly procedure for the industry to determine the degree of whiteness of a particular piece of white gold jewellery.
Colour, of course, can be measured quantitatively in a reproducible way. The conditions of measurement, especially the incident lighting, are important. Generally a ‘Northern Daylight’ illumination is preferred. The degree of whiteness of a white gold can be described in terms of a numerical parameter called the ASTM Yellowness Index: 1925 and is calculated from the basic tri-stimulus values, X, Y & Z, measured with a colour spectrophotometer. The lower the value, the whiter is the gold. [For more information on this parameter, see the scientific article by Manchandra and Henderson in Gold Bulletin, volume 38 (2) which will be published in June 2005 on the website, www.goldbulletin.org]
The Guidelines: [1] Definition of White Gold
White gold has been defined as having a Yellowness Index value of 32.0 or less.
This is additionally limited in terms of CIELab co-ordinates as having an L value of at least 75, and an a* value between +3.0 and –3.5
Measurement conditions are:
Illuminant C (D65 is a close approximation), observer angle 2°, specular and ultraviolet components included. Samples polished to 6 micron finish.
Such measurements should be carried out in a light box with the correct lamp or at least under a lamp with a D65 illuminant. These are available through the MJSA or directly through Gretag MacBeth.
The Guidelines: [2] The Grades of White Gold
Within the definition of the colour of white gold , it is proposed that 3 grades of white gold are defined:
• GRADE 1 (Premium white grade) – these alloys have a good white colour and do not need rhodium plating.• GRADE 2 (Standard grade) – reasonable white colour; rhodium plating is optional for these alloys• GRADE 3 (Off-white colour) – such alloys need to be rhodium plated
Any alloys falling outside of these three grades are classed as non-white. In terms of the Yellowness Index, these grades can be defined as follows,
Table 2 Grades of white in white golds
Grade
Yellowness Index value
Grade 1 (Premium)
<>32.0
Application of the Guidelines: The Whiteness Index
For many retailers and manufacturers, quantitative measurement of white golds for whiteness, using a colour spectrophotometer instrument is not practical or ecomomical. This problem has been overcome by the development of The Whiteness Index, a colour chart, by the Munsell laboratories of Gretag-McBeth Inc. This colour chart comprises 7 metal foil based samples spanning the range of Yellowness Index values covered by the 3 grades within the overall definition. Using the correct lighting conditions, the Whiteness Index enables a speedy and easy comparison of the whiteness of a piece of white gold against the samples and thus facilitating an estimate of which grade it is and its Yellowness Index value.
Application of the Guidelines: Implications for the trade1. It is envisaged that jewellery retailers and manufacturers will increasingly specify the grade of white when placing orders with their suppliers. At the top end of the market, there will be a preference to specify Grade 1 or possibly Grade 2 alloys in the appropriate caratage.At the lower, mass end of the market, where price is important, many will prefer to specify the off-white Grade 3 and to rhodium plate the jewellery. It is notable that many carat gold alloy suppliers are already defining their range of white golds in terms of the 3 grades (and the grade selected will be reflected in the price; the Grade 1 alloys will include high palladium alloys and so tend to be more expensive).
2. It should be noted that the Grades of white gold are based solely on colour (whiteness) and not on alloy composition. Thus, any of the grades can include nickel-containing alloys that may not comply with the European Directive on nickel.
3. In the case of customer complaints concerning the underlying poor colour of white golds, when the rhodium plating wears through, it should be easy, using the Whiteness Index, to establish if the jewellery alloy complies with the industry definition of white gold or lies outside. If outside of the definition, the retailer is vulnerable in cases of litigation. A good reason to specify the Grade when ordering jewellery from their supplier!
The Whiteness Index
4. It is not envisaged that the grade of white gold used in a piece of jewellery will be disclosed to the customer. The grades are intended solely for use within the trade. However, it is an option for retailers (and manufacturers) to disclose to their customers whether the white gold jewellery is rhodium plated. This is a commercial decision! However, there is a body of opinion that failure to disclose rhodium plating could be in breach of national trade laws in many countries where there is a requirement on descriptions of products to be full and accurate.
5. For information about purchasing the Whiteness Index and/or lightboxes or lamps, contact the MJSA: e-mail: mjsa@mjsainc.com or http://www.mjsainc.com/ ; tel: +1 401 274 3840; fax: +1 401 274 0265
Read a paper on white gold from the Santa Fe Symposium. (1,698 kb) Click hereSource: WGC
For many retailers and manufacturers, quantitative measurement of white golds for whiteness, using a colour spectrophotometer instrument is not practical or ecomomical. This problem has been overcome by the development of The Whiteness Index, a colour chart, by the Munsell laboratories of Gretag-McBeth Inc. This colour chart comprises 7 metal foil based samples spanning the range of Yellowness Index values covered by the 3 grades within the overall definition. Using the correct lighting conditions, the Whiteness Index enables a speedy and easy comparison of the whiteness of a piece of white gold against the samples and thus facilitating an estimate of which grade it is and its Yellowness Index value.
Application of the Guidelines: Implications for the trade1. It is envisaged that jewellery retailers and manufacturers will increasingly specify the grade of white when placing orders with their suppliers. At the top end of the market, there will be a preference to specify Grade 1 or possibly Grade 2 alloys in the appropriate caratage.At the lower, mass end of the market, where price is important, many will prefer to specify the off-white Grade 3 and to rhodium plate the jewellery. It is notable that many carat gold alloy suppliers are already defining their range of white golds in terms of the 3 grades (and the grade selected will be reflected in the price; the Grade 1 alloys will include high palladium alloys and so tend to be more expensive).
2. It should be noted that the Grades of white gold are based solely on colour (whiteness) and not on alloy composition. Thus, any of the grades can include nickel-containing alloys that may not comply with the European Directive on nickel.
3. In the case of customer complaints concerning the underlying poor colour of white golds, when the rhodium plating wears through, it should be easy, using the Whiteness Index, to establish if the jewellery alloy complies with the industry definition of white gold or lies outside. If outside of the definition, the retailer is vulnerable in cases of litigation. A good reason to specify the Grade when ordering jewellery from their supplier!
The Whiteness Index
4. It is not envisaged that the grade of white gold used in a piece of jewellery will be disclosed to the customer. The grades are intended solely for use within the trade. However, it is an option for retailers (and manufacturers) to disclose to their customers whether the white gold jewellery is rhodium plated. This is a commercial decision! However, there is a body of opinion that failure to disclose rhodium plating could be in breach of national trade laws in many countries where there is a requirement on descriptions of products to be full and accurate.
5. For information about purchasing the Whiteness Index and/or lightboxes or lamps, contact the MJSA: e-mail: mjsa@mjsainc.com or http://www.mjsainc.com/ ; tel: +1 401 274 3840; fax: +1 401 274 0265
Read a paper on white gold from the Santa Fe Symposium. (1,698 kb) Click hereSource: WGC
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