SIST EN ISO 11426:1999

SLOVENSKI STANDARD
SIST EN ISO 11426:1999
01-november-1999
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SIST EN 31426:1998
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Determination of gold in gold jewellery alloys - Cupellation method (fire assay) (ISO
11426:1997)
Bestimmung von Gold in Gold-Schmucklegierungen - Dokimatisches Verfahren (ISO
11426:1997)
Dosage de l'or dans les alliages d'or pour la bijouterie-joaillerie - Méthode de
coupellation (essai au feu) (ISO 11426: 1997)
Ta slovenski standard je istoveten z: EN ISO 11426:1998
ICS:
39.060 Nakit Jewellery
SIST EN ISO 11426:1999 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN ISO 11426:1999

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SIST EN ISO 11426:1999

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SIST EN ISO 11426:1999

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SIST EN ISO 11426:1999

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SIST EN ISO 11426:1999

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SIST EN ISO 11426:1999
INTERNATIONAL ISO
STANDARD 11426
Second edition
1997-12-01
Determination of gold in gold jewellery
alloys — Cupellation method (fire assay)
Dosage de l'or dans les alliages d'or pour la bijouterie-joaillerie — Méthode
de coupellation (essai au feu)
A
Reference number
ISO 11426:1997(E)

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SIST EN ISO 11426:1999
ISO 11426:1997(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide
federation of national standards bodies (ISO member bodies). The work of
preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which
a technical committee has been established has the right to be represented
on that committee. International organizations, governmental and non-
governmental, in liaison with ISO, also take part in the work. ISO
collaborates closely with the International Electrotechnical Commission
(IEC) on all matters of electrotechnical standardization.
Draft International Standards adopted by the technical committees are
circulated to the member bodies for voting. Publication as an International
Standard requires approval by at least 75 % of the member bodies casting
a vote.
International Standard ISO 11426 was prepared by Technical Committee
ISO/TC 174, Jewellery.
This second edition cancels and replaces the first edition ISO 11426:1993,
which has been technically revised.
©  ISO 1997
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced
or utilized in any form or by any means, electronic or mechanical, including photocopying and
microfilm, without permission in writing from the publisher.
International Organization for Standardization
Case postale 56 • CH-1211 Genève 20 • Switzerland
Internet central@iso.ch
X.400 c=ch; a=400net; p=iso; o=isocs; s=central
Printed in Switzerland
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SIST EN ISO 11426:1999
INTERNATIONAL STANDARD  © ISO ISO 11426:1997(E)
Determination of gold in gold jewellery alloys —
Cupellation method (fire assay)
1 Scope
This International 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 (�).
The procedure is applicable specifically to gold alloys incorporating silver, copper and
zinc. Some modifications are indicated where nickel and/or palladium are present in the
so-called white gold alloys, as well as for alloys containing 990 or more parts per
thousand (�) of gold.
This method is intended to be used as the reference method for the determination of
fineness in alloys covered by ISO 9202.
2 Normative reference
The following standard contains provisions which, through reference in this text,
constitute provisions of this International Standard. At the time of publication, the edition
indicated was valid. All standards are subject to revision, and parties to agreements
based on this International Standard are encouraged to investigate the possibility of
applying the most recent edition of the standard indicated below. Members of IEC and
ISO maintain registers of currently valid International Standards.
ISO 9202:1991, Jewellery — Fineness of precious metal alloys
3 Principle
The gold alloys are inquarted with silver, compounded with lead and cupelled in a
cupellation furnace until a precious metal button is obtained. After flattening and rolling,
the silver is extracted (parted) in nitric acid and the gold weighed. Possible systematic
errors in the procedure are eliminated by assaying standard proof samples in parallel.
NOTE — White gold alloys containing palladium and/or nickel as well as alloys with 990 or more
parts per thousand (�) of gold require some procedural changes.
4 Reagents
During the analysis, unless otherwise stated, use only reagents of recognized analytical
grade and only distilled water or water of equivalent purity.
1

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SIST EN ISO 11426:1999
© ISO
ISO 11426:1997(E)
4.1 Nitric acid, 33 % (m/m) (ρ = 1,2 g/ml), free of halides.
20
4.2 Nitric acid, 49 % (m/m) (ρ = 1,3 g/ml), free of halides.
20
4.3 Lead, assay grade, free of precious metals and bismuth, as foil, beads or tablets.
4.4 Silver, for inquartation, minimum purity 999,9 parts per thousand (�) by mass,
free of gold and platinum group metals.
4.5 Pure gold, for proof samples
– for determination of gold between 333 and 990 parts per thousand (�) by
mass, minimum purity 999,9 parts per thousand (�) by mass;
– for determination of gold more than 990 parts per thousand (�) by mass,
minimum purity 999,99 parts per thousand (�) by mass.
4.6 Palladium, for proof samples, minimum purity 999,9 parts per thousand (�) by
mass, free of gold and other platinum group metals.
4.7 Nickel, for proof samples, minimum purity 999 parts per thousand (�) by mass,
free of gold and platinum group metals.
4.8 Copper foil or wire, minimum purity 999 parts per thousand (�) by mass, free of
gold, and platinum group metals.
4.9 Borax (Na B O ), anhydrous.
2 4 7
5 Apparatus
Ordinary laboratory apparatus and the following.
5.1 Cupellation furnace, in which an oxidizing atmosphere can be maintained.
CAUTION — A standard muffle furnace is not satisfactory for this purpose.
5.2 Magnesium oxide cupels, usually of diameter 22 mm to absorb 6 g lead, or of
diameter 26 mm to absorb 10 g lead, or blocks of cupels of similar absorption.
5.3 Parting flasks or platinum basket.
5.4 Parting cups, comprising unglazed porcelain crucibles.
5.5 Cuppellation tongs.
5.6 Assay pliers.
5.7 Polished anvil, which may be replaced by a press, polished and reserved for this
purpose.
5.8 Polished hammer, of minimum mass 400 g, which may be replaced by a press,
polished and reserved for this purpose.
5.9 Scorification dishes, usually of diameter 50 mm.
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SIST EN ISO 11426:1999
© ISO
ISO 11426:1997(E)
5.10 Jewellers' rolls.
5.11 Platinum-tipped crucible tongs.
5.12 Assay cleaning brush, of stiff bristle or nylon but not brass.
6 Sampling
The sampling procedure for jewellery gold alloys shall be agreed upon until a
corresponding standard method has been published.
For coated articles, appropriate precautions that have been agreed shall be taken to
exclude the coating from the determination.
7 Procedure
NOTE — When the composition of the samples is unknown, use a preliminary assay for the
estimation of the fineness of gold. For the distinction between palladium and nickel white golds,
the touch stone test can also be used. If the cornet breaks up during the parting process, this is
often an indication of excess silver.
7.1 Yellow gold alloys
7.1.1 Analysis samples
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 + beads) should be at least 4 g for yellow gold samples up to 200 mg, and 6 g for
samples from 201 mg to 300 mg (250 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.
7.1.2 Proof assay samples
Weigh, as in 7.1.1, at least two proof assay samples of proof 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 7.1.3 and 7.1.4 in the same
manner.
7.1.3 Cupellation and treatment of precious metal buttons
Place the assay and the proof assay samples (7.1.2), tightly wrapped in lead f
...