ISO 11426-2014 pdf free download

ISO 11426-2014 pdf free download.Jewellery Determination of gold in gold jewellery alloys Cupellation method (fire assay)
Joaillerie — Dosage de I’or dans les alliages d’or pour Ia bijouteriejoai llerie — Méthode de coupellation (essai aufeu).
7.2 Yellow and red gold alloys, free of nickel, and palladium white gold alloys
7.2.1 Assay sample
Transfer at least two samples of the alloy, preferably between 125 mg and 250 mg. weighed to the nearest
0,01 mg, into assay-grade lead foil (4.3). The mass of the foil (or foil and beads) should be at least 4 g for
considered gold alloy samples up to 200 mg, and 6 g for samples from 201 mg to 300 mg. Add pure silver
(4.4) equivalent to 2,3 to 3 times the mass of fine gold present. Roll and compress the lead foil into a tight ball.
7.2.2 Proof assay samples
Weigh, as in Z2J. at least two proof assay samples of pure gold (4.5) and pure silver (4,4) in masses which correspond to the expected gold and silver contents (including the inquartation addition) of the assay sample. The total content of base metals in the assay samples is taken into consideration by the addition of a corresponding quantity of copper.
Treat the proof assay samples and the assay samples in 72.3 and 72.4 in the same manner.
7.2.3 Cupellation and treatment of precious metal buttons
Place the assay and the proof assay samples (Z2.,2), tightly wrapped in lead foil, on magnesia cupels (5.3), which have been preheated to at least 1 000 °C in the cupellation furnace (&2).
Place the cupels with the proof assay samples as close as possible to the corresponding assay samples in the cupellation furnace maintained at 1 050 °C to 1150 °C. Continue heating (about 25 mm) under oxidizing conditions until the cupellation process is completed. Remove the cupels from the furnace. Allow the precious metal buttons to cool down before lifting them from the cupels with the assay pliers (51). Squeeze the buttons and brush their undersides carefully with a brush (5.U) to remove any adhering cupel material. Flatten the beads on the polished anvil (5.) with a polished hammer (5.9) and anneal by heating just to red heat.
Roll them into 0,12 mm to 0,15 mm thick strips and anneal again. Roll the strips into comets without contamination or loss of gold.
The cupel should be examined carefully to ensure that the precious metal bead contains all gold of the sample. If small droplet residues are present, a full assay has to be repeated.
7.2.4 Parting of the silver/gold samples
CAUTION — For the parting operations with nitric acid, a fume hood should be kept clean and used exclusively for this determination.ISO 11426-2014 pdf free download.