VOCABULARY TERM: PROOF FINISH, PART 1

Proof Finish. A very highly reflective metallic surface, mirror-like, produced by striking from specially treated highly polished dies and specially prepared polished blanks. Proof finish dates back to the 18th century (the first use of the term "proof" as applied to coins and medals is as early as 1762 in England). The concept was to display a perfect impression from a new die in all its sharp and fresh condition before any production run and wear was made from it. Even the name proof indicates – like a first copy of a print – the earliest and sharpest impression. Also called "specimen" or "master" coins in early US Mint documents and literature. The concept of mass produced "first impressions" did not occur until the 20th century with the boom of coin collecting.

Until the availability of reliable multi-strike presses in the late 1960s, all proof coins were made on a medal press using one blow from the dies.

Today mirror-like proof coins are made by polishing the dies and the planchets until the result is a mirror image surface on the struck piece. Now we have production run proof coins in the millions, and private mints issuing proof medals in the hundreds of thousands.

Proof finish, which starts with a craftsman in a die department (or tool and die department), is prepared by polishing the proof surface area in each die. The die itself is created by any normal method – hand cut or machined, cut by pantographic reduction or hubbed. The basic die is no different from any other production run die.

Proof polishing is done by a craftsman with a hand-held grinding wheel and a polishing compound, usually diamond dust or emery applied first and rouge afterwards. It should be emphasized that proof finish is in the die before the piece is struck – a proof finish cannot be applied to an already struck piece.

Full proof versus prooflike. A full proof or brilliant proof must have the full treatment of proof polishing and struck on polished blanks. Prooflike are struck from dies that have been augmented. After several hundred impressions proof dies often require another polishing treatment of the dies to effect a longer die life. After several thousand impressions a full proof die may exhibit wear.

To lengthen the life of the die, dies may be plated with chromium or nickel before they are placed in production – this results in a struck piece of high luster and looks almost like a full proof surface, but this is not a true proof surface. Pieces struck from any plated dies are prooflike. Thus without knowledge of the state of the die, whether the die has been plated or not and the type of planchets used, it is nearly impossible to differentiate between the two terms. It is understandable these terms are confused by the person viewing a struck specimen.

Matte proof finish. Some proof surface pieces have a portion of the surface with little or no reflective area – called matte (or mat surface). This is intended for artistic effect of contrast between high reflective proof areas and low reflective matte area.

The matte portion of the die is created with a treatment of dilute acid to lightly etch the surface. The acid is usually hydrochloric acid; it is available in a commercial matte chemical (see matte dip) or some diemakers make their own acid etching solution. The same matte effect can be obtained by light sandblasting (abrasive blasting) the surface (after masking off the area to be proof finished). Such matte finish is also called frosted surface.

Treating dies for proof finish. Dies are given a proof finish after they are fully cut and turned off to the proper profile to fit the intended press. To be able to strike a proof surface, each die must be given a proof surface (by proof polishing with diamond dust – called a polishing compound – and rouge using a power wheel).

Proof polishing is a low tech operation. Usually there are specially trained craftsmen who do this at a mint with long proof die production runs. It is usually women who are trained to do proof polishing because they are adept in such delicate and intricate work. The die is locked in a vise and the surface is coated first with diamond dust and the surface is polished with a hand-held grinding wheel and polished again with rouge. In medallic plants proof polishing is done in the tool and die department.

Proof polishing produces a brilliant mirror-like surface on the die that will strike a similar surface on the struck piece. Also dies can be treated for a matte proof finish by lightly etching the desired surface with acid or by light abrasive blasting.

When a die has both matte and proof surfaces, the matte is applied first. Matte solution is applied directly to the sunken portion of the die's design – usually the device – where the dilute acid is allowed to minutely etch the surface. It creates microscopic bites or cups. It must be immediately rinsed off to stop the etching action of the acid. During this procedure an unskilled craftsman could easily apply the acid to the area of the die that is intended to be proof polished. Such unintended etching is called a foul bite.

The proof polish is always done after the matte treatment of the die. Also for cameo proof surfaces the polishing is always done in full or in part of the field or background. This is done for several reasons: it is the highest portion of the die (easiest to proof polish), the lowest portion of the struck piece (which is protected somewhat by the rim and higher relief), and is usually the largest smooth area in a coin design (to emphasize the mirror surface).

Types of proof coin finishes. Numismatists have created a terminology to describe a number of proof treatments that have appeared on coins in the 20th century. Listed here are the most noted of these proof finishes:

• Brilliant Proof. The entire die surface is proof polished and this die is struck on highly polished, highly reflective planchets, the treatment is also called full proof. This produces a brilliant, mirror finish of the highest reflective surface. As an example U.S. proof coins of 1936-42 were issued in this brilliant proof finish.

• Frosted Proof. Any portion of a die is acid etched matte – usually the device – with all remainder brilliant proof. The device is lowest in the die, it is acid etched first, then the remainder of the die is proof polished. It is struck on polished planchets. Much of the charm of a frosted proof coin is the contrast between the two proof treatments to the design on each side. In general sculptors and coin designers did not like mirror-like finishes because they felt it interfered with their designs.

• Cameo Proof. A frosted proof usually with a portrait as device and lettering, both of which is matte with the background or field is brilliant proof. Cameo proofs must be struck on polished planchets.

• Matte Proof. The entire surface of the die is acid treated (or abrasive blasted) for a dull reflective surface. Typically struck on selected planchets. In US coinage terminology a "matte proof" is created by sandblasting or etching the die face prior to hardening of the die. This was used on Lincoln cents from 1909-1916 and Buffalo nickels from 1913 to 1916. It has not been used on any other U.S. coins.

• Sandblast Proof. A sandblast proof coin was made by striking a selected planchet with new dies using a medal press. The resultant satin coin was highly detailed. This was manually sandblasted much in the manner of a medal. Extremely fine-grain sand was used although the grit size varies from one production batch to another. Acid was never used for this purpose at U.S. Mints. Gold proof coins were sandblasted in 1908 and 1910-1915. Additional pre-production proofs were sandblasted for 1921 and 1922 Peace dollars and many commemorative half dollars. The purpose for these latter uses was to display the design to its maximum artistic effect.

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

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