Due to their chemical and physical properties, precious metals are increasingly used in a variety of industries, including jewelry, art, coinage and exchange, fuel cells, man-made fibers, computers and other electronics, medicine and pharmaceutical products, and manufacturing. The unique properties of precious metals, along with their relative scarcity, dictate a high demand and value in the marketplace. Alloying a precious metal with one or more other metals or non-metals, or plating or washing an article with a precious metal to increase aesthetic appearance is often done to reduce expense but can result in non-uniform distribution of precious metals throughout an article and articles of dubious provenance are often poorly prepared. This can often alter properties of such objects, and can be particularly detrimental to the functioning of articles that will be used for functional purposes beyond mere aesthetic appearance, such as noted above. It can also affect even the value of aesthetic articles, such as jewelry, art, and coinage depending on the impurity content present. Determining the composition of precious metallic samples and items accurately and quickly, while minimizing the alteration of the sample in the process, is desirable when evaluating the sample for potential usefulness and pricing.
There are some long-standing analytical techniques currently available to determine the nature, content and components of items that contain precious metals. Some analytical methods use an electrochemical process to evaluate the purity of precious metals. For example, U.S. Pat. No. 4,799,999 teaches a method whereby the specimen is wetted with an electrolyte, a small current then anodizes the surface of the specimen for a metered period of time, a sensing device is then applied to the charged surface and observes the potential decay, which is then interpolated with empirical data to determine the karat quality of a gold alloy.
As another example, U.S. Pat. No. 5,218,303 concerns a method where a controlled amount of electrolyte is deposited on a sample of precious metal alloy, an electrode is placed in contact with the sample and electrolyte through which an electric current is applied to create an electrolyte paste. As the current decays to an asymptotic level, a second and third pulse of electric current are applied and the measured electrical conductance is compared to a table of standards.
Another testing device includes a handheld applicator to apply a testing solution. For example, U.S. Pat. No. 6,103,194 concerns a handheld applicator for testing metallic items and includes a housing that surrounds an insert containing a reservoir with a testing chemical and an applicator, which applies the testing chemical to the surface of the metal.
U.S. Pat. No. 5,888,362 concerns a handheld probe having an electrode embedded in an electrolyte in a reservoir of the probe and arranged to conduct electrically with the sample through the electrolyte and a fibrous tip. A battery is coupled to a calibration potentiometer and the sample in circuit to form a galvanic cell.
These devices have one or more limitations that have prevented them from gaining widespread acceptance in the industry. Thus, an improved testing device and methods according to the invention described below have been desired to expedite economical testing of precious metal objects.