CEN/TC 283/WG 1 - Sampling and analysis

This Technical Report specifies an acceptance sampling system of single sampling plans both for inspection by attributes and for inspection by variables. The attributes plans are of the accept-zero form, i.e. no lot is accepted if the sample from it contains one or more nonconforming articles. (For the purposes of this Technical Report, a nonconforming article is a precious metal article containing less than the nominal proportion by weight of the precious metal). The variables plans generally require smaller sample sizes than the attributes plans, but require the precious metal content of all the sampled articles to exceed the nominal content by at least a specified amount.
The objective of this Technical Report is to provide accept-zero schemes and procedures for assuring an upper limit to the long-term percentage of nonconforming precious metal articles in the market place (i.e. the percentage of articles reaching the market place that contain less than the nominal proportion of precious metal) by means of the lowest practicable sample sizes. The upper limit provided by this Technical Report is 1,47% nonconforming. The objective is achieved in three ways:
a)   the sample size reduces as the total number of articles accepted in all the lots since the last non-acceptance increases;
b)   if quality is consistently high, then subject to certain conditions it will be possible to switch from sampling by attributes to sampling by variables;
c)   under sampling by variables, further reductions in sample size may be achieved by switching from the unknown standard deviation method (the "s" method) to the known standard deviation method (the "s" method) if there is sufficient evidence that the process standard deviation is constant....

This European Standard specifies the precious metal content in solders suitable for use in the production of jewellery made of precious metal alloys.

Defines ring-size as inner circumference of the ring measured in mm.

Specifies a limited number of colours to assist trading. The test is performed by spectral reflectance measurement in accordance with CIE Publication No 38.

Specifies a gravimetric method for the determination of platinum in platinum jewellery alloys, preferably within the range of fineness stated in ISO 9202. The procedure applies specifically to platinum alloys incorporating palladium, iridium, rhodium, copper, cobalt, gold, ruthenium, gallium, chromium, indium and less than 5 % tungsten. Some modifications are indicated where palladium, iridium, rhodium, gold or ruthenium are present.

Specifies a gravimetric method for the determination of palladium in palladium jewellery alloys, preferably within the range of fineness stated in ISO 9202. These alloys may contain silver, indium, gallium, copper, cobalt, nickel, tin and ruthenium. Coprecipitated elements have to be determined by a suitable method and a correction applied.

Specifies a gravimetric method for the determination of platinum in platinum jewellery alloys, preferably within the range of fineness stated in ISO 9202. These alloys may contain palladium, iridium, rhodium, copper, cobalt, gold, ruthenium, gallium, chromium, indium and less than 5 % tungsten. Some modifications are indicated where palladium, iridium, rhodium, gold or ruthenium are present.

The principle of the method specified is dissolving the sample in dilute nitric acid and determining the silver content of the resulting solution by titration with standard potassium bromide solution, using a potentiometric indication of the equivalence point. The alloys, preferably within the range of fineness stated in ISO 9202, may contain copper, zinc, cadmium and palladium. Apart from palladium, which must be precipitated before commencing titration, these elements do not interfere with this method of determination.

Specifies a range of fineness of gold alloys (375, 585, 750, 916), platinum alloys (850, 900, 950), palladium alloys (500, 950), and silver alloys (800, 835, 925).

This standard specifies a cupellation method (fire assay) for the determination  of gold in gold jewellery alloys. The gold content of the alloys should preferably lie between 333 and 999 parts per thousand.

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