JPH0217075B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for testing the purity of precious metals, in particular gold and silver, as used in gold and silver jewelry for jewelry, and advantageous methods for carrying out the method. This relates to test kits (combined equipment).

Both silver and gold are hallmarked for the purpose of indicating the gold or silver content in a particular jewelry item. Hallmark counterfeiting is not unknown, and in some countries the indications of gold content and percent purity of silver are generally imprecise and ambiguous.

If the handler wishes to check the true content, he must perform a subjective test, for example by applying nitric acid to the surface of the gold article. The degree of discoloration of the ensuing acid attack zone is highly dependent on the silver content or amount of the base metal with which the gold is alloyed, generally copper, zinc and nickel. Test results are relative and their accuracy is therefore dependent on the experience and judgment of the tester. After testing, discolored areas must be removed by sanding.

It is clear that this established method is not satisfactory.

The present invention seeks to provide a method for testing the purity of a precious metal when it is alloyed with a base metal, which (a) has an MOH (Mohs) hardness of 7 to 8;
(b) applying a test liquid to the sample, in which case the test liquid is For samples on the order of 9 carats, contain a suitable concentration of nitric acid to dissolve the expected base metal content of the sample, and for samples on the order of more than 9 carats, to dissolve the expected base metal content of the sample. (c) shall contain a mixture of nitric and hydrochloric acids of a suitable concentration to dissolve with the prescribed portion of the gold content; This includes determining that additional testing is necessary if partial or complete disappearance of the test occurs.

The present invention also provides a test kit for testing the purity of precious metals when they are alloyed with base metals, which includes (a) a test kit having a MOH hardness of 7 to 8; , moderately abrasive, comparatively dark color,
(b) containing nitric acid at a concentration sufficient to dissolve the expected base metal content for samples of 9 carats, or to dissolve the base metal content of the sample for samples larger than 9 carats; a container containing a mixture of nitric and hydrochloric acids at a concentration capable of dissolving the gold along with a predetermined portion of the expected gold content.

The choice of stone is important, especially with regard to its hardness. The darker the stone, the easier it will be to see the sample scraped from the article. Mineral acid mixtures for gold contain hydrochloric acid and nitric acid. Preferably, the proportions of the acid mixture and the overall normality of the mixture are adjusted to each commonly used purity level of the precious metal of interest. For example, gold jewelry is adjusted to 9 carats and 18 carats.

Referring to the drawing, a flat plate 2 made of black onyx with a size of 10 mm x 10 mm x 4 mm is shown.
is shown and is rubbed onto a 9 karat gold bracelet, for example. A group of visible yellow scratch lines are left on the plate as shown in FIG. Only a small amount of the bracelet needs to be scraped off to give a sample. Dripping tool 8
Dropper 6 contains 6.6N nitric acid, which is
Prepared from concentrated nitric acid supplied to laboratories at 63%.

A drop of nitric acid is placed on the sample as shown in FIG. After a few seconds, the wet part of the sample will become thinner and thinner. After about 60 seconds the reaction stopped and the sample remained.

Three separate bottles are prepared for 14, 18 and 22 carat alloys, grades commonly used by jewelry manufacturers. A mixture of nitric acid and hydrochloric acid is shown below. These are supplied to the Institute63
% concentrated nitric acid and 36% hydrochloric acid.

14 carat test mixture 1.35 ml of 36% hydrochloric acid added to 8.35N nitric acid prepared by diluting 63% nitric acid to make the whole
Reduced to 1000ml.

18 carat test mixture 11.0 ml of 36% hydrochloric acid added to 8.3N nitric acid prepared by diluting 63% nitric acid to make a total
It was made into 1000ml.

24 carat test mixture 149 ml of 36% hydrochloric acid was made up to 1000 ml with 9N nitric acid prepared by diluting 63% nitric acid.

If a bracelet is labeled as 9 carats, it contains a large amount of base metals. Base metals produce most of the yellow color in the sample marks on the flat plate. Nitric acid dissolves the base metals and leaves the gold intact. If it is not exactly 9 karat, the sample will melt and the gold content will be more difficult to see because there will be more base metal present than there should be for a 9 karat alloy.

If the sample remains undissolved, it is 9 carats or more. For the next test, a drop of acid from a 14 carat test mix is placed on the same mark. If it melts, the bracelet is over 9 carats and probably 9
~13 carat range.

If the sample is certified as 18 carats, a drop of the 18 carat test mixture is placed on the mark. If it remains, it is 18 carats or more, and the test with 22 carats is repeated first. The concentration of the acid mixture is calculated to be chemically equivalent to one carat less than each of the 9, 14, 18 and 22 carats used in the jewelry industry. A 22-carat mixture may dissolve all of the 22-carat sample over time, but the 22-carat mixture is acceptable for testing.
It cannot be dissolved within minutes. Only some of the base metals and gold are melted during the test period.

The percentages of the acid mixture proportions are thus taken as follows: Carat Nitric Acid % Hydrochloric Acid % 9 100 0 14 99.865 0.135 18 98.9 1.1 22 85.1 14.9 A % variation of about 5% is acceptable.

Any remaining deposits can be easily rubbed off with the aid of common abrasive cleaners.

Kits for platinum, rhodium and silver are similarly prepared.

The advantages of the invention are: 1. The article itself is not discolored or etched by the test.

2 The test is more specific than prior art methods.

3. Results can be easily determined even by inexperienced testers.

4 For gold, the test can discern a difference of two carats.

[Brief explanation of drawings]

Figure 1 shows the test kit; on the left is a plan view of the quartz sample collection plate; on the right is a front view of the dropper with the cap open; and Figure 2 shows the alloy scraped from a small piece of jewelry. A collection plate holding a sample is shown, FIG. 3 shows the state immediately after a drop of the test liquid is dropped, and FIG. 4 shows the result after 50 seconds for a sample whose purity is below the guaranteed label. 2: Sample collection plate, 4: Sample, 6:
Bottle, 8: Dripping tool.

Claims (1)

[Claims] 1. A method for testing the purity of a noble metal when the noble metal is alloyed with a base metal, comprising: (a) having an MOH (Mohs) hardness of 7 to 8;
(b) applying a test liquid to the sample, in which case the test liquid is For samples on the order of 9 carats, contain a suitable concentration of nitric acid to dissolve the expected base metal content of the sample, and for samples on the order of more than 9 carats, to dissolve the expected base metal content of the sample. (c) shall contain a mixture of nitric and hydrochloric acids of a suitable concentration to dissolve with the prescribed portion of the gold content; A precious metal purity test method that includes determining that additional testing is necessary if partial or complete disappearance of . 2. A test kit for testing the purity of precious metals when they are alloyed with base metals, comprising: (a) a moderately abrasive comparative dark color for taking samples having an MOH hardness of 7 to 8; (b) containing nitric acid at a concentration sufficient to dissolve the expected base metal content for samples of 9 carats, or to dissolve the base metal content of the sample for samples larger than 9 carats; a container containing a mixture of nitric acid and hydrochloric acid at a concentration capable of dissolving a predetermined portion of the expected gold content. 3 Claim 2 in which the stone is synthetic quartz
Test kit as described in section.