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White Gold has risen in popularity over the past few years and so have the number of queries from consumers and jewelers as to what exactly can be called “White”. To date there has been no established or recognised means of defining the composition of White Gold, nor the colour it should be. Confusion and inconsistency reign.
In response to this problem, the Birmingham Assay Office launched an initiative in November 2003 to establish a recognised retail definition of White Gold. This activity was strongly supported by Dr Chris Corti, Director of International Technology for the World Gold Council who was leading a similar initiative in the USA.
The Problem
It is acknowledged that there are huge variations in the colour of white gold on sale and also in the expectations of the consumer. White Gold alloy is usually bleached by the addition of silver, palladium or nickel, or a combination of all three. Predictably the result of these compositional differences is quite a significant variation in colour, from dull grey to brown yellow. It is accepted practice to plate white gold items with between 0.05 and 0.5 microns of Rhodium to produce a bright, white and uniformly finished article. While this is makes the new item very attractive, it has inevitably led to problems as the Rhodium plating will eventually wear off, revealing a variety of disappointing colours underneath the plating.
Research
The Birmingham Assay Office formed a working group including representatives from major retail groups, and Cookson Precious Metals Ltd. The members determined that the main objective was not to define metallurgical composition, but to establish a measure of the colour itself which is what matters most to the consumer. Whatever standards were established therefore had to apply to the visual appearance of the metal rather than its content.
Research was carried out by Dippal Manchanda of the Birmingham Assay Office and Steven Henderson, Metallurgical Manager of Cookson Precious Metals Ltd. Their extensive investigations produced the grading structure defined below. The color of over 70 gold alloys was measured using a spectrophotometer, a special camera that measures the color of reflected light. From these measurements a grading structure was established. These instrument measurements were also confirmed through a series of visual assessments.
The grading structure uses a numerical scale to indicate how white an alloy is. The scale runs from 1 (exceptionally white) to 32 (worst acceptable white) and is broken up in to 3 grades (a rhodium-plate gives a reading of 6.8).
Category Value Description
Grade 1 < 19 Good White. Does not need Rhodium plating
Grade 2 19 – 24.5 Reasonable White. Option to Rhodium plate
Grade 3 24.5 - 32 Poor White (Incomplete bleaching). Needs to be Rhodium plated
Non-white > 32 Not acceptable as a White
The World Gold Council have accepted this grading structure for white gold alloys and are now briefing this message to the jewellery industry.
If you require any further information regarding the grading of white gold alloys please contact: Dippal Manchanda, Chief Assayer
Birmingham Assay Office, Birmingham B3 1SB, England
Email : dippal.manchanda@theassayoffice.co.uk Tel 00 44 121 236 6951
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