BS EN ISO 8654-2018 pdf free download.Jewellery – Colours of gold alloys – Definition, range of colours and designation (ISO 8654:2018)
5 Colour measurement
5.1 General
Two methods are available to determine the colour, a quantitative method (see 5.2) and a qualitative method by visual comparison (see 5.3).
5.2 Quantitative method
5.2.1 Preparation of the samples
5.2.1.1 General
The samples to be measured shall have a flat and polished surface to be used as a measurement area.
The measurement area shall be exempt of defect.
The finishing (polishing and washing) shall be (re)done until a mirror surface is achieved (Y reaches a constant value).
After polishing, the sample colour measurement shall be made within 120 min maximum.
NOTE Polishing, washing and environment conditions can greatly affect the colour.
5.2.1.2 Metallographic preparation
Metallographic preparation is made with a final polishing with broadcloth charged with an abrasive solution. The solution contains 1 µm sized abrasive particles.
5.2.1.3 Sample cleaning
The recommended sample cleaning is done by gently wiping the surface with a clean soft cloth (microfibre) and some isopropylalcohol (IPA).
5.2.2 Measurement apparatus
5.2.2.1 General
The measurement apparatus for the colour measurement of a gold alloy shall be in accordance to CIE Publication No. 15.
5.2.2.2 Reference apparatus
The reference apparatus for the colour measurement of a gold alloy is an integrating sphere spectrophotometer able to measure spectral reflectance, with a measurement geometry compatible with designation di:8° or 8°:di (specular component included).
NOTE Other measurement geometries can be used as long as they do not affect significantly the colour results compared to the described measurement geometry.
5.2.2.3 Spectrophotometer setup
Before making any measurement, the apparatus shall be set up with the following parameters:
— Specular Component Included (SCI);
— Standard illuminant D65;
— Standard observer 2°.
5.2.3 Measurement method
Measure the spectral reflectance.
The measured values in the xyY colour space shall be expressed with 4 significant digits for x and y and 1 significant digit for Y.
The measured or converted values in the L*a*b* colour space shall be indicated with 2 significant digits for a* and b* or C* and h and 1 significant digit for L*.
The colour measure is an average of 5 distinct measurements of the sample (after repositioning) ensuring to revolve it between each measurement.
5.3 Qualitative method
For (visual) comparison purposes of the sample, it is possible to use a range of polished colour slips.
A preparation of colour slips is described in Annex A.
6 Gold alloy colours
Nominal values and tolerances of colours are given in Table 2, 3 and 4 in accordance with 5.2.
Figures 1, 2, 3, 4 illustrate graphically nominal and tolerances values.
NOTE The eye of a trained person can see colour differences even within a tolerance range.BS EN ISO 8654 pdf download