Its function was to supervise the annual testing of the gold, silver, and (in its final years) base metal coins produced by the United States Mint to ensure that they met specifications.

Although some members were designated by statute, for the most part the commission, which was freshly appointed each year, consisted of prominent Americans, including numismatists.

Hamilton concluded his report: The remedy for errors in the weight and alloy of the coins, must necessarily form a part, in the system of a mint; and the manner of applying it will require to be regulated.

The following account is given of the practice in England, in this particular: A certain number of pieces are taken promiscuously out of every fifteen pounds of gold, coined at the Mint, which are deposited, for safe keeping, in a strong box, called the pix [sic, more commonly "pyx"].

In addition to setting the standards for the new nation's coinage, Congress provided for an American version of the British Trial of the Pyx: That from every separate mass of standard gold or silver, which shall be made into coins at the said Mint, there shall be taken, set apart by the Treasurer and reserved in his custody a certain number of pieces, not less than three, and that once in every year the pieces so set apart and reserved, shall be assayed under the inspection of the Chief Justice of the United States, the Secretary and Comptroller of the Treasury, the Secretary for the Department of State, and the Attorney General of the United States, (who are hereby required to attend for that purpose at the said Mint, on the last Monday in July in each year) ... and if it shall be found that the gold and silver so assayed, shall not be inferior to their respective standards herein before declared more than one part in one hundred and forty-four parts, the officer or officers of the said Mint whom it may concern shall be held excusable; but if any greater inferiority shall appear, it shall be certified to the President of the United States, and the said officer or officers shall be deemed disqualified to hold their respective offices.

Numismatist Fred Reed suggested that the delay was probably due to poor weather, making it difficult for officials to travel from the new capital of Washington, D.C., to Philadelphia for the assay.

The 1806 and 1815 sessions were delayed because of outbreaks of disease in Philadelphia; the one in 1812 was held a month late because of a heavy snowstorm which prevented the commissioners from reaching the Mint.

[9] With the Coinage Act of 1834, Congress removed the automatic disqualification of Mint officers in the event of an unfavorable assay, leaving the decision to the president.

[17] The act also changed the officers required to serve on the Assay Commission: That to secure a due conformity in the gold and silver coins to their respective standards of fineness and weight, the judge of the district court of the United States for the eastern district of Pennsylvania, the Comptroller of the Currency, the assayer of the assay-office at New York, and such other persons as the President shall, from time to time, designate, shall meet as assay-commissioners, at the mint in Philadelphia, to examine and test, in the presence of the Director of the Mint, the fineness and weight of the coins reserved by the several mints for this purpose, on the second Wednesday in February, annually.

[21] In the early 20th century, the San Francisco Mint struck silver coins for the Philippines, then a US possession; those pieces were included in the assay.

The procedure was changed so that the Mint Director submitted the names of more individuals than would actually be appointed to the White House, where the final choices were made.

The Mint Director received nominations for assay commissioner from legislators, political organizations, government officials, and from members of the public.

Commissioners could instead test 21,975 dimes and 11,098 quarters, all made from copper-nickel clad,[24] though as the Associated Press, reporting on the 1973 Assay Commission, put it, "a discovery of a bum coin hasn't occurred in years.

[33] At the 1974 meeting, one copper-nickel Eisenhower dollar was discovered which weighed 15 grains (0.97 g) below specification; after reference to the rules, the coin was deemed barely within guidelines.

Numismatist Charles Logan, in his 1979 article about the impending end of the Assay Commission, stated that this incident pointed out "the basic problem with the annual trial.

"[34] In early 1977, outgoing Mint Director Mary Brooks sent a list of 117 nominees to the new president, Jimmy Carter, from which it was expected that about two or three dozen names would be selected.

Carter refused to make any public appointments, feeling the Assay Commission was unneeded given that the Mint performed the same work through routine internal checks and that the $2,500 appropriated each year was a poor use of taxpayer money.

[36] The 1979 meeting, attended by the government-employed commission members and Mint Director Stella Hackel Sims, was held eight days late on February 22 due to schedule conflicts.

[35][42] The general function of the Assay Commission was to examine the gold and silver coins of the Mint and ensure they met the proper specifications.

[46] By statute passed in 1911, the commission was required to inspect the weights and balances used in assaying at the Philadelphia Mint, and to report on their accuracy.

[20][48] According to a description of the 1948 meeting, silver coins selected for assay were first placed between steel rollers until the thickness was reduced to .0001 inches (0.0025 mm), and then were chopped into fine pieces and dissolved in nitric acid.

The recordholder as a presidential appointee is Dr. James Lewis Howe, head of the Department of Chemistry at Washington and Lee University, 18 times an assay commissioner, serving in 1907 and then each year from 1910 to 1926.

[53] An employee of the National Bureau of Standards was included in the presidential appointments each year;[3] he brought with him the weights used in the assay, which were checked by the agency in advance.

[55] The three known specimens of the 1873-CC quarter, without arrows by the date, and the only known dime of that description, may have been salvaged from assay pieces, as the remainder of those coins had been ordered melted as underweight.

[13] A similar mystery attends the 1894 Barber dime struck at San Francisco (1894-S) of which the published mintage is 24, although it is not certain whether this total includes the one sent to Philadelphia to await the 1895 Assay Commission.

When President Carter stopped appointing public members to the commission in 1977, the OTACS fundraised in an unsuccessful attempt to induce the government to continue that tradition.

[31][57] With the number of surviving OTACS members at less than three dozen, the society plans no further meetings; its 2012 session in conjunction with the ANA convention in Philadelphia included an event at the mint.

The initial purpose in having medals struck was not principally to provide keepsakes to the assay commissioners, but to advertise the Mint's medal-striking capabilities.

[62] The 1870 obverse, by Longacre's successor William Barber, features Moneta surrounded by implements of the assay, such as scales and the pyx.

[64] The 1920 reverse, by Engraver George T. Morgan, had a design which symbolized the ending of World War I; in 1921, an extra medal was struck in gold, given by the assay commissioners to outgoing President Woodrow Wilson as a mark of respect.