Die Polishing (DPL)
Die polishing is the deliberate abrading of a die face to remove clash marks or other damage so the die can stay in service. Error-Ref files it as "intentional die abrasion," and notes that its chief result is a lowering of the die face that can remove shallow design elements. On struck coins it shows as fine raised lines, thinned or missing design detail, or both. While all dies receive some degree of finishing during manufacture, the DPL designation refers to the visible aftereffects of in-service polishing performed during the die's production run.
How Does It Happen?
Die polishing is not an accident: it is maintenance done on purpose, so that a die with clash marks or surface damage can go back into the press instead of being retired.
The polishing process involves several stages and motivations:
- Proof die finishing: Proof dies have their fields polished to produce mirror surfaces, and Error-Ref lists over-polished proof and Special Mint Set dies, and fields lowered or design removed by proof polishing, as their own entries.
- Clash mark removal: When dies clash (meet without a planchet between them), each die face picks up an impression of the other design. Abrading the die to remove those clash marks is the classic reason for polishing. Error-Ref's examples include a 1983-P Jefferson nickel whose dies were abraded to remove a strong clash, leaving heavy scratches running in many directions.
- Damage repair: Other surface damage on the die face can sometimes be abraded away without retiring the die.
- Dies that need extra work: Coin World's "About VAMs" column notes that all Reverse of 1878 Morgan dollar working dies needed an unusual amount of polishing because the design was too flat to coin well, and that the work left some dies over-polished.
Because abrasion lowers the die face, heavy polishing removes not only the defect but also the shallowest parts of the design. Error-Ref illustrates this with a 1972-D cent missing low-lying details of Lincoln's bust and a 1984-P Jefferson nickel with thinned 8 and 4 and a nearly erased P mint mark.
How to Identify Die Polishing
Die polishing evidence manifests in several ways on struck coins:
- Raised lines: The most direct evidence. Scratches left in the die face by the abrasive show as fine raised lines on the coin. Error-Ref notes that scratches from deliberate abrasion are usually fine and run in many directions.
- Detail loss: Areas that have been aggressively polished show reduced design sharpness. Hair strands merge, feather details flatten, lettering edges soften, and fine design elements become indistinct. Compare the affected area to a coin from an early die state to see the difference.
- Clash evidence removal: If earlier coins from the same die show clash marks and later ones lack them, the die was abraded in between. Weakened clash marks alongside new polish lines point the same way.
- Design truncation: On heavily polished dies, the lowest-relief parts of the design disappear entirely. Error-Ref's examples include several Buffalo nickel varieties (see below).
Die Polishing vs. Weak Strike vs. Die Wear
These three conditions all produce coins with softened design details, but the causes differ:
| Condition | Cause | Key Diagnostic |
|---|---|---|
| Die polishing | Mechanical removal of die surface | Polishing lines visible; detail loss concentrated in polished areas |
| Weak strike | Insufficient striking pressure | Even detail weakness; opposite side also weak; no polishing lines |
| Die wear | Gradual erosion from repeated striking | Progressive weakening across the die's run; no polishing lines; most severe at high points |
Notable Examples
Proof Die Polishing Lines
Because proof dies are polished to mirror fields, raised polish lines are a familiar sight on proof coins. Raised polish lines on a proof are from the die; incuse hairlines are from cleaning or handling after striking.
Morgan Dollar Die States
Morgan dollar (1878-1921) die varieties, catalogued as VAMs (Van Allen-Mallis), record many polished die states. Coin World's "About VAMs" column describes one 1878 obverse die that appears first, sharp, on VAM-189 and later, after an attempt to remove clash marks, on VAM-188 and VAM-223, where the L of LIBERTY and the coronet band are washed out.
Buffalo Nickels
Several Buffalo nickel (1913-1938) varieties come from die polishing. Error-Ref attributes the 1937-D "three-legged" and 1936-D "3½-legged" nickels to die abrasion that removed part of the bison's foreleg, and the "Two Feather" variety to abrasion during clash removal that took away the small part of the third feather behind the Indian's neck.
1955 Doubled Die Obverse Lincoln Cent
Even the 1955 doubled die cent shows polishing. According to PCGS (as cited by Wikipedia), genuine 1955 doubled die cents show vertical die polishing lines to the left of the T in CENT, and the lines are used as an authentication marker.
Collecting Tips
- Die state collecting: Die polishing is a key marker for die state identification. Variety specialists track polishing events to establish the sequence of a die's life: fresh die, clash, polish, and so on. Each polishing event creates a new die state.
- Raised versus incuse: Die polish lines are raised, because they were cut into the die. Fine incuse lines are hairlines from cleaning or handling. A raised line alone does not prove a coin was never cleaned, so look at the whole surface.
- Use die markers: Polish lines in a fixed place, like those beside the T of CENT on the 1955 doubled die, help match a coin to a known die.
- Doubled dies and polishing: Polishing a doubled die can weaken its doubling, so early and late die states of the same variety can look different. Compare with reference photos of the die state.