Walter Breen
Proofs struck subsequent to the introduction of close collars (1828/36-1916) will, in addition to the above, also show much stronger borders than uncirculated coins, with sharp clear border beads nowhere blurred and nowhere running into the plain raised rim; some, though not all, will show traces of a knife-rim at outermost part of rim on obv. or rev. or both; edges will be sharply defined and polished; there will be no trace of frostiness (from cold flow of metal) near or within any letters, around stars, or near borders; in some cases, rims will be wider than on normal uncirculated coins. Nickel proofs sometimes constitute exceptions to all this. A coin cleaned with ammonia or any of the more drastic chemical agents such as cyanide will often not be decidable by these criteria, as these chemicals destroy proof surface by dissolving and leaching away microscopic oxide or sulfide coatings, or - in the case of cyanide - dissolving the metal itself.
These criteria apply as well to foreign proofs of the early and middle 19th century. One does get into difficulties with certain crowns of George III dated from 1817 to 1820, as individual specimens were made with such care from polished dies as to make the question almost unanswerable of whether they were intentional brilliant proofs.
Seaby's English Silver Coins, p.5, provides the detail that in some 19th and 20th century British proofs, devices were rendered frosty by treating intaglio areas on dies with weak acid, presumably before polishing the fields. I do not know if this was ever done at the United States mint, and tend to doubt it. I do know that as the dies wore down, frostiness on the devices tended to disappear on both British and American proofs; frosted heads and eagles on modern (post-1936) American proofs are very unusual, and the only sets dated after 1950 in which all coins show frosted devices (as was routine in the 19th century) are those assembled by collectors.
Canadian proofs, before introduction of the decimal coinage in 1858, are a group as rare and unusual as American Colonial proofs. I have seen proofs of the 1837 Bank tokens ("Papineaus"), 1844 Front View Bank tokens, 1852 river-god bank tokens, 1843 and 1856 official penny and halfpenny pieces, and a few others, the 1843 and 1856 coins having come from the Royal Mint in London, the others from private establishments (Boulton & Watt's Soho Mint and its successor Ralph Heaton & Sons, Birmingham). Without exception, these rare proofs show every earmark of having been made by the identical processes used on official British proofs of the period. These were substantially identical to those used on later American proofs. The same comment holds for Canadian patterns of the period and those commonly assimilated to the Canadian series (e.g. the 1823 copper Fiftieth and Hundredth of a Dollar). The 1858 Canadian proofs, commonly occurring with plain edges like many silver British proofs of the period, were made in the Royal Mint in London -as in fact were later Canadian decimal proofs prior to about 1908 -and they were made by the same processes.
British proof copper coins from the 1820's on no longer show file marks on edges, and they were struck in close collars; edges are brilliant as though polished, and in every other way they indicate that the moneyers in the Royal Mint had installed equipment similar to Boulton's. Some British proof silver coins, though not all, come with lettered edges. Seaby lists several of these with blundered edges (transposed words!) indicating that not the Castaing machine but some version of the virole brisee was used on them. This, of course, must have slowed up production considerably; the problem of rapid coinage using a virole brisee or segmented collar die was not solved until early in the 20th century. In every instance, the difficulty was to make a contrivance which would retract the three, four or six segments of the collar die rapidly and smoothly without shearing off edge lettering or causing the newly minted coin to stick to the collar die after striking. I do not have details on that used now, unfortunately.
AFTERMATH: TECHNOLOGY REPLACES ART
Except for nickel coins, proofs made in the middle and later years of the 19th century at the Philadelphia Mint are a fairly monotonous lot of coins. "Polished-up portraits of the coinage" (as Dr. Sheldon calls them), they have little individuality and any two of the same year and denomination will look very much alike. That the nickel coins are an exception testifies largely to Mint difficulties with nickel, which remained until well into the 20th century. Nickel is very rough on dies: they wear down fast, they break down fast, they often produce only indifferent impressions on nickel planchets even on proofs. Don Taxay has quoted contemporaneous hostile Mint opinions of nickel as a coinage metal. Of all the alloys of nickel tried, only two - 80 copper: 20 nickel, common in the United Kingdom to the present day, and 75 copper: 25 nickel, adopted in the U.S. since 1865 - have proved at all practical for coinage, and even those two only marginally so. Alloys with less than 12% nickel tend to be very yellow and brassy in appearance; alloys with over 30% nickel generally yield ingots riddled with bubbles and altogether unsuitable for the rolling and cutting processes. Nickel proofs from the Philadelphia mint - and to a lesser extent from the British mint - have often fallen short of the quality of other proofs. I have seen coins of proof-only dates or varieties (e.g. 1865 "double date west" 3¢ nickel, 1866 5¢ nickel with center dot on rev., 1877 and 78 3¢ and 5¢ nickel, 1887/6 3¢ nickel) with the typical proof surface, but poorly struck on borders and edges, often with designs not too well brought up, and very often indeed on planchets thickly seeded with minute defects. As late as the early 1890's, nickel 5¢ pieces in proof sometimes come only with a dull matte-like surface, explanation unknown; apparently the nickel strips simply refused to take a high polish. I have seen nickel proofs of the 1950's which were almost as bad, being identifiable as proofs only by the borders, rims and edges. Authentication of copper-nickel proof cents is a task calculated to give a conscientious numismatist nightmares, so uneven is the quality of the real ones.
On the other hand, low-mintage silver and gold coins in the 1880's often come with brilliant surfaces very near indeed in appearance to those of proofs, and decisions of the proof or nonproof status of some of these coins are equally eye-taxing. That uncirculated coins have been found in proof sets of 1866 and some other years, straight from the mint, makes the problem still more difficult. I have already quoted the criteria in use; in difficult borderline cases, often the only thing to do is compare the disputed coins with known proofs from original sets. And if there is still doubt, do not sell the coin as a proof.
It may be appropriate here to bring up the matter of restrikes. Most restrikes are nominally proofs, whether minted from original dies or from made-to-order copy dies ("novodels") in the mint of origin, or made clandestinely by private parties. The privately made ones, though usually struck from polished or even lapped dies on polished blanks, are hardly ever of the quality of authentic mint products and do not merit further discussion here. On the other hand, we have items like the half-cents of the 1840's, 1856 flying eagle cents, 1863-64 trimes and half-dimes, 1873 2¢ and $3, 1875 $3, 1865 gold dollar and $3, 1827 quarters, 1801-3, "1804," 1836-39 and 51-53 silver dollars, and others, which were made to order as favor coins by employees at the Philadelphia Mint, sometimes from original dies with new reverses, often lapped to the extent that details are narrowed or even obliterated, or in other instances from dies similar to originals and created by punching old date logotypes into new (undated) dies. Some of the more clandestine restrikes show evidence of gross rust or die failure - this is most of all true of certain patterns. Others, especially in the half cent series, show die buckling, weakness, rude striking and extremely high knife-rims - occasionally these are removed by filing. In every instance such coins were made by processes enough different from the originals so that trained numismatists can "smell them a yard away," save for a few late ones such as the 1865 gold dollar and $3 which required no different processes and which were probably made only a few years later than their dates.