Later in the 20th century abrasive blasting was done with glass particles because the grit size could be smaller. This created tiny pits that had different characteristics than those made with mineral abrasives. To partial treat a die's surface would require masking or use of a jig to prevent the blasting to any desired surface, a somewhat complicated procedure. Thus most such dies were given this treatment to the entire die's surface. Selected and lightly polished planchets could be used.

A type of matte proof in which the texture is provided by sandblasting the die with extremely fine-grain sand. Even so the minute cavities created by the sand particles are larger than acid etched cavities. Later in the 20th century abrasive blasting was done with glass particles because the grit size could be smaller. To partial treat a die's surface would require masking or use of a jig to prevent the blasting to any desired surface, a somewhat complicated procedure. Thus most such dies were given this treatment to the entire die's surface. Selected and lightly polished planchets could be used.

• Satin Finish Proof. A satin proof was made by using new dies to strike a selected planchet using a high pressure medal press. This transferred maximum detail from the dies to the coin and resulted in a coin with smooth, satin-like fields that mimicked those of a new die. There was no post-production treatment.

• Reverse Proof. Mirrorlike surface on the devices and lettering only with background or field in a satin matte finish. It is the "reverse" of the customary cameo proof where the devices are satin matte and background is proof polished. Polished planchets must be used.

• High Relief Proof. A medal of typical high relief is given proof polishing to effect the entire surface. This was first done in 1968 in New York City by Medallic Art Company which struck the Martin Luther King Junior Memorial Medal by Abram Belskie (1968-065) in full proof for the 1½-inch (39.8mm) size.

See also reflectiveness, abrasive blasting, masking.

Striking proof finish coins. All efforts in proof coining is to make all detail and edges as sharp as possible. Specially prepared dies and specially prepared blanks are struck for a heavier press impression with meal forced into every point of die cavity and knurl if reeded. Also the metal is forced to the utmost point of rim/edge juncture. In effect, the most obvious diagnostic point of proof surface is this sharpness, particularly with a sharp rim/edge juncture in addition to the mirror reflectiveness. Should a proof surface item be handled, mishandled, be exposed to certain chemical environments (those with benzine creates a haze for example), the mirror surface is sure to disappear. The sharpness of the striking may still exist, however.

Any type press can strike proof coins at pressure that are higher than normal.

Screw presses were ideal for proof coining, as are traditional coining presses. Hydraulic press can be used for the ease of obtaining greater pressure but are far slower for production runs (after 1936). The Philadelphia Mint used a screw press for proof coins in the 19th century in the same manner as sinking a die.

The planchet was struck once This transferred the maximum detail to the coin. After the late 1960s, multiple striking of a double blow could insure sharper detail. Presses capable of multiple striking became available in Germany. These were able to give the planchet two or more blows in very rapid succession while maintaining precise alignment between planchet and dies.

[RWB3] After ejection from proof striking, proof coins are carefully processed untilpackaged. If they need to be handled in quantity they are placed in tote boxes lined with antitarnish paper.

Striking proof finish medals. Small proof surface medal are struck in the same manner as for coins. Larger medals in proof surface, particularly after 1990 are struck only on hydraulic presses. Die and planchet preparation is the same, but the medals are retrieved from the press manually, inspected by the pressman who places the medal in a tote box lined with antitarnish paper.

Mirror-like proof finish is a very fragile state of metal surface. Proof surfacesare extremely vulnerable to atmosphere and the environment. Any wear, tarnish, toning, handling or mishandling diminishes the reflectiveness and surface condition of proof finish. Extreme care must be exercised in the handling, storing, displaying, mounting and transporting of proof surface coins and medals to preserve this fragile state.Once the proof surface has deteriorated, nothing can be done to restore it. Thusproof finish coins and medals are never candidates for repair or refinishing and catalogs describe such deteriorated items as "toned proof," "former proof," "extra fine proof" and such.

(After having said that nothing can be done to restore proof finish - which is true- a toned proof or deteriorated proof surface can be given an oxidized and relieved surface, in effect eliminating the proof surface entirely. This gives the item a very permanent oxidized finish. When producing both proof surface and oxidized varieties of the same item in the same diameter (as U.S. Inaugural medals) manufacturers will strike the proof finish variety first. An unsatisfactory proof finish can be salvaged as a very satisfactory oxidized variety.)

Proof anomalies. Because proof surface dies must be polished to create the surface, overpolishing is a hazard. When this is done to extreme - as to remove clash marks say - some detail becomes obliterated. The most obvious of overpolishing is the disappearance of engraver's initials. This occurred at the Philadelphia Mint in 1936 to 1942 proof half dollars (removing the AAW monogram of artist Adolph Weinman).

Also there exists what numismatic cataloger Walter Breen calls one-sided proof coins. In only eight instances in all U.S. coinage history did he find coins that bore a proof polished die on one side, and an unpolished die on the other. In all instances the obverse bore the proof surface, the reverse unpolished. This occurred for bronze as well as silver coins, from 1817 (50-cent, Breen 4632) to 1873 (25-cent, Breen 4064).

Protective housing of proof surface pieces necessary. From the very first proof surface coinage it was recognized such pieces must be protected. Coins with proof surfaces were issued in cases, even sets in the 18th century. Medals were struck in proof surface prior to coins, but the British found an unusual way to protect the first proof surface medals. They housed them in watch cases! Even today we see Pitt Club Medals - the first numismatic items issued in proof surface - still housed in original 18th century watch cases. See watch case mounting.

In the late 20th century a small industry aose to supply manufactured products, including plastic holders, containers, envelopes and such to house proof surface objects.

References:
C50 {1965} Breen [The Proofing Process].
NC11 {1988} Breen

To read the complete entry on the Newman Numismatic Portal, see:
Proof Finish(https://nnp.wustl.edu/library/dictionarydetail/516560)

To read the earlier E-Sylum article, see:
VOCABULARY TERM: PROOF FINISH, PART 1(https://www.coinbooks.org/v27/esylum_v27n43a19.html)