ASTM E1335-08(2017)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: E1335 − 08 (Reapproved 2017)
Standard Test Methods for
Determination of Gold in Bullion by Fire Assay Cupellation
Analysis
This standard is issued under the fixed designation E1335; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope E50 Practices for Apparatus, Reagents, and Safety Consid-
erations for Chemical Analysis of Metals, Ores, and
1.1 These test methods cover cupellation analysis of bullion
Related Materials
having chemical compositions within the following limits:
E135 Terminology Relating to Analytical Chemistry for
Element Concentration Range, %
Metals, Ores, and Related Materials
E173 Practice for Conducting Interlaboratory Studies of
Gold 0.5 to 4.0 and 20.0 to 99.8
Silver 1.0 to 99.5
Methods for Chemical Analysis of Metals (Withdrawn
Total gold plus silver 75.0 to 100.0
1998)
1.2 These test methods appear in the following order:
E1601 Practice for Conducting an Interlaboratory Study to
Sections
Evaluate the Performance of an Analytical Method
20.0% – 99.0% gold 10–17
3. Terminology
0.5% – 4.0% gold 18–23
98.9% – 99.8% gold 24–30
3.1 Definitions—For definitions of terms used in these test
1.3 The values stated in SI units are to be regarded as
methods, refer to Terminology E135.
standard. No other units of measurement are included in this
3.2 Definitions of Terms Specific to This Standard:
standard.
3.2.1 anneal—a thermal treatment to change the properties
1.4 This standard does not purport to address all of the
or grain structure of the product.
safety concerns, if any, associated with its use. It is the
3.2.2 cupel—a small, shallow, porous cup, usually made of
responsibility of the user of this standard to establish appro-
bone ash or from magnesium oxide.
priate safety and health practices and determine the applica-
bility of regulatory limitations prior to use. For specific safety 3.2.3 cupellation—an oxidizing fusion of lead, sample base
hazards, see Section 8. metals and gold, and silver in a cupel. The lead is oxidized to
1.5 This international standard was developed in accor- litharge (PbO); other base metals which may be present, such
dance with internationally recognized principles on standard- ascopperandtin,areoxidizedaswell.Theoxidizedmetalsare
ization established in the Decision on Principles for the absorbed into the cupel, leaving a gold and silver doré bead on
Development of International Standards, Guides and Recom- the cupel surface.
mendations issued by the World Trade Organization Technical
3.2.4 doré bead—a gold and silver alloy bead which results
Barriers to Trade (TBT) Committee.
from cupellation.
3.2.5 inquartation—theadditionofsilvertoanassaysample
2. Referenced Documents
to enable parting.
2.1 ASTM Standards:
3.2.6 part—the separation of silver from gold by selectively
B562 Specification for Refined Gold
dissolving the silver in acid, usually nitric acid (HNO ).
3.2.7 proof—a synthetic standard having a composition
These test methods are under the jurisdiction of ASTM Committee E01 on
similar to the test sample.
Analytical Chemistry for Metals, Ores, and Related Materials and are the direct
responsibility of Subcommittee E01.05 on Cu, Pb, Zn, Cd, Sn, Be, Precious Metals,
3.2.8 proof correction—analyzing the proof concurrently
their Alloys, and Related Metals.
with the test sample and using the results to correct the final
Current edition approved Jan. 15, 2017. Published March 2017. Originally
assay.
approved in 1990. Last previous edition approved in 2008 as E1335 – 08. DOI:
10.1520/E1335-08R17.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on The last approved version of this historical standard is referenced on
the ASTM website. www.astm.org.
Copyright ©ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA19428-2959. United States
E1335 − 08 (2017)
4. Significance and Use 7.5 Nitric Acid, 0.0002 % chloride, maximum.
4.1 Thesetestmethodsareintendedforthedeterminationof 7.6 Cupels—Magnesium oxide or bone ash.
thegoldcontentofgoldandsilverbullion.Itisassumedthatall
8. Hazards
who use these test methods are trained assayers capable of
performing common fire assay procedures skillfully and safely.
8.1 For precautions to be observed in the use of certain
It is expected that work will be performed in a properly
reagents and equipment in these test methods refer to Practices
equipped laboratory.
E50.
8.2 Use care when handling hot crucibles and operating
5. Interferences
furnaces to avoid personal injury by either burn or electrical
5.1 If the bullion contains any of the following elements in
shock.
excess of the concentrations shown, the accuracy and precision
8.3 Lead and litharge (PbO) are toxic materials and are
requirements of these test methods may not be achieved.
volatile at low temperatures. Avoid inhalation, ingestion, or
Element Maximum Level, %
skin contact.
Arsenic 2.0
Antimony 2.0
9. Sampling
Bismuth 2.0
Iron 2.0
9.1 Use shot or pin tube samples. Brush the samples to
Nickel 2.0
remove any adhering glass or flux.
Platinum group, total (Ir, Os, Pd, Pt, Rh, Ru) 0.01
Selenium 2.0
9.2 Prepare shot samples from molten metal poured into
Tellurium 2.0
water. Use only whole single pieces between 1 mm and 3 mm
Thallium 2.0
Tungsten 0.5 in diameter.
Zinc 5.0
9.3 Pin tube samples are prepared from molten metal drawn
6. Apparatus
intovacuum-evacuatedglasstubes.Breaktheglassandinspect
the samples to ensure that they are not hollow and that they are
6.1 Assay Furnace—Capable of temperatures up to
free from slag and inclusions.
1100 °C, accurate to 6 10 °C, with draft controls and fume
9.3.1 Roll the samples lengthwise on a clean rolling mill to
hood.
0.127 mm, then clean them with alcohol.
6.2 Hammer.
9.3.2 Cutthestripintohorizontalslicestoobtainthedesired
6.3 Hammering Block. sample weight.
6.4 Rolling Mill. 9.4 Drillings are not usually as representative of a melt as
pin tube or shot samples. If bar drillings are to be analyzed,
6.5 Analytical Balance.
obtain them as directed in Specification B562.
6.5.1 For Test Methods A and B, capable of weighing to
0.01 mg.
TEST METHOD A
6.5.2 For Test Method C, capable of weighing to 0.002 mg.
10. Scope
6.6 Parting Basket—Platinum basket or porcelain gooch
crucibles in stainless steel basket/vessel.
10.1 This test method covers cupellation analysis of gold in
6.6.1 Gooch Porcelain Crucible—13 mL capacity, bottom
bullion containing 20.0 % to 99.0 % gold and 1.0 % to 80.0 %
inside diameter (ID) 18 mn, top ID 29 mn.
silver.
6.6.2 Stainless Steel Basket—316 stainless steel.
10.2 This international standard was developed in accor-
dance with internationally recognized principles on standard-
7. Reagents
ization established in the Decision on Principles for the
7.1 Copper Metal, 99.9 % purity, minimum; 0.0005 % gold,
Development of International Standards, Guides and Recom-
maximum.
mendations issued by the World Trade Organization Technical
7.2 Gold Metal, 99.99 % purity, minimum.
Barriers to Trade (TBT) Committee.
7.2.1 Gold metal, 99.999 % purity, minimum for Test
11. Summary of Test Method
Method C only.
11.1 A preliminary assay is performed to estimate the
7.3 Lead Foil, 99.99 % purity, minimum (0.001 % silver,
approximate gold content and approximate gold plus silver
maximum; 0.0005 % gold, maximum).
content. Other methods such as X-ray fluorescence (XRF),
7.4 Silver Metal, 99.9 % purity, minimum (0.0005 % gold,
inductively coupled plasma emission (ICP), direct current
maximum).
plasma emission (DCP), or atomic absorption spectroscopy
(AAS) can also be used for a preliminary assay if they have
Reagent Chemicals, American Chemical Society Specifications, American
been shown to have an accuracy of better than 6 1 % for gold
Chemical Society, Washington, DC, www.chemistry.org. For suggestions on the
and 6 2 % for silver. The sample is weighed and silver or
testing of reagents not listed by the American Chemical Society, see the United
copper, or both, added if necessary.The sample is wrapped and
States Pharmacopeia and National Formulary, U.S. Pharmacopeial Convention,
Inc. (USPC), Rockville, MD, http://www.usp.org. compacted in lead foil and cupelled to remove base metals,
E1335 − 08 (2017)
then parted in nitric acid. The insoluble portion is weighed to hammer to loosen any adhering cupel material. Remove the
determine the gold content. Proof standards are used for remaining traces of cupel material with a stiff brush.
correction of systematic gravimetric errors.
12.3.3 Form Coronet—Flatten the beads for the gold deter-
mination on an anvil with a hammer and taper the edges to
12. Approximate Assay
facilitate rolling.
12.3.4 Annealtheflattenedbeadstoatemperatureof650 °C
12.1 Perform a preliminary assay first on the test sample to
to 700 °C. Pass the beads through a rolling mill to form an
establish a suitable composition for the proof correction
elongated strip about 10 cm long and 0.015 cm to 0.03 cm in
standard and inquarting silver.
thickness, maintaining a uniform thickness throughout the
12.2 Approximate Gold Plus Silver Content—Weigh one
batch of samples. Reanneal the strips and then roll each into a
500 mg 6 2-mg sample to the nearest 0.1 mg. Weigh a portion
loose spiral (or coronet) with the bottom side facing outward.
of lead foil in accordance with the following:
12.3.5 Parting:
Estimated Total Gold Plus Silver, % Weight of Lead Foil, g
12.3.5.1 Place each coronet in a suitable parting container
(50-mL porcelain crucible, 50-mL Florence flask, or 50-mL
95.0–100.0 5.0
75.0–95.0 10.0
Erlenmeyer flask). Add 25 mL of preheated HNO (1 + 2) and
heat at just below the boiling point for 45 min. The coronet
12.2.1 Wrap the sample in the lead foil.
must remain completely immersed throughout the parting
12.2.2 Cupellation—The cupels are placed in rows in the
process. Decant and discard the solution. If the coronet breaks
section of the furnace having the most uniform temperature
apart, care must be taken not to lose any gold pieces.
gradient.After the lead foil packets are prepared, place them in
the assay furnace on cupels which have been preheated to
NOTE 2—Parting baskets should not be used when determining the
900 °C for 20 min with the draft slightly open. The furnace
approximate gold content of multiple samples. If a coronet breaks apart,
temperature is correct if the dark crust which forms over the
it will contaminate the other parted samples.
melted lead packet disappears within a few minutes. A typical
12.3.5.2 Add 25 mLof HNO (2 + 1) and heat at just below
temperature to produce such reasonably rapid “opening up” of
the boiling point for 45 min. The coronet must remain
the samples is 900 °C.
completely immersed throughout the parting process. Decant
12.2.3 After the lead packets have opened up adjust the
and wash the gold three times with 25 mL of water.
airflow through the furnace. The temperature must be main-
12.3.5.3 Dry the gold on a hotplate, then anneal it to
tained high enough to prevent the button from freezing (the
between 650 °C and 700 °C. Cool the gold and weigh to the
solidification of molten litharge on the button surface).
nearest 0.1 mg.
12.2.4 Keep the cupels in the furnace until all traces of lead
12.3.5.4 Calculate the approximate gold content as follows:
have disappeared. This time depends on the amount of lead
G 5 C/W 3100 (2)
~ !
used, the furnace temperature, and the airflow (Note 1).
a
Remove the cupels and slowly cool them to room temperature
where:
either by placing cupels at the entrance of the furnace with the
G = approximate gold, %,
a
door open or by placing a warmed metal spatula on top of the
C = weight of gold, g, and
cupels.
W = weight of sample, g.
NOTE 1—Occasionally at the end of the cupellation process, the beads
12.4 Approximate Silver Content—Calculate the approxi-
will visibly brighten or “flash.”This is a result of the sudden release of the
mate silver content as follows:
latent heat of fusion as the lead-free bead solidifies.
S 5 T 2 G (3)
12.2.5 Remove the test samples and any proof beads from a a a
the cupels, place them on edge and tap them lightly with a
where:
hammer to loosen any adhering cupel material. Remove the
S = approximate silver, %,
a
remaining traces of cupel material with a stiff brush.
T = approximate total gold plus silver, % (12.2.6), and
a
12.2.6 Weigh the doré bead to the nearest 0.1 mg and
G = approximate gold, % (12.3).
a
calculate the approximate gold plus silver content as follows:
12.5 Approximate Base Metal Content— Calculate the ap-
T 5 ~D/V! 3100 (1)
a
proximate base metal content, as follows:
where:
M 5 100 2 T (4)
a a
T = approximate total gold plus silver, %,
a
where:
D = weight of the doré bead, g, and
M = approximate base metal content, %, and
V = weight of the sample, g.
a
T = approximate gold plus silver, % (12.2.6).
a
12.3 Approximate Gold Content—Weigh one 500 mg 6
2-mg test sample to the nearest 0.1 mg.Add 1.25 g 6 0.05 g of
13. Proof Standard Preparation
inquarting silver and 0.05 g 6 0.010 g copper. Wrap the
sample with additions in lead foil as directed in 12.2. 13.1 Prepare two proof standards, each containing gold,
12.3.1 Cupel as directed in 12.2.2 – 12.2.4. silver, and copper in the amounts listed as follows. Wrap each
12.3.2 Remove the test samples and any proof beads from proof in lead foil in accordance with 12.2 and proceed to
the cupels, place them on edge and tap them lightly with a 12.2.2.
E1335 − 08 (2017)
13.1.1 Gold—The weight of gold must be within 65mgof P 5 Q/O (7)
the approximate gold content (12.3). Weigh the gold to the
where:
nearest 0.01 mg and use this weight for calculating the proof
P = proof correction,
correction (15.3).
Q = weight of gold added, g, and
13.1.2 Silver—The weight of inquarting silver is 2.5 times
O = weight of gold found, g.
the approximate gold content (12.3). Weigh the silver to the
A successful analysis should have proof corrections falling
nearest 10 mg.
between 0.99XX and 1.00XX. (See supporting data and
13.1.3 Copper—If the approximate base metal content
ASTM proficiency test program for gold in bullion.)
(12.5) of the sample is less than 1 %, add 0.05 g 6 0.01 g of
¯
copper metal to each proof. If the approximate base metal
15.4 Average the two proof standard corrections, P.
contentisgreaterthan1 %,theamountofcopperisequalto
...