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What is a proof stamp?

A mirror stamp—known internationally as Proof (English) or PP—Polierte Platte (German)—is a method of preparing stamps and discs and a special minting process that gives...

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  • Author of the entry: Mennica Skarbowa
  • Date of entry:

A mirror stamp – known internationally as Proof (English) or PP – Polierte Platte (German) – is a method of preparing stamps and discs and a special minting mode that gives coins a mirror-like finish and a matte relief (contrasting "mirror + matte"). This finish is created mainly with collectors in mind.

Table of contents

How is a coin with a mirror stamp made?

  • Specially prepared discs (planchets). Planchets for Proof coins are cleaned and polished (burnished) to reduce micro-scratches and achieve a uniform, smooth surface.
  • Polished and selectively matted stamps. The stamps are highly polished (to achieve a mirror effect on the fields), and the elements of the design are matted (nowadays most often by laser), giving the relief a "frosty" appearance.
  • Multiple, slower strikes. Proof coins are struck at least twice (often more slowly and with greater care) to perfectly "press" the metal into the finest details of the design. Circulation/BU coins usually receive a single strike.

The side effects of this diligence are usually sharper ranciska (edges) and a very clean, "black" mirror of the fields.

Proof vs BU vs UNC — the most important differences

  • Proof (mirror stamp): Polished planchets and stamps, selective matting of the relief, at least double striking, outstanding depth of detail and contrast. Collector's item.
  • BU - Brilliant Uncirculated (colloquially referred to as "mint condition"): New coins, minted once on newer dies and under stricter controls than circulation coins; lack the mirror-like fields typical of Proof coins. Often used in bullion versions.
  • UNC - Uncirculated: A coin that is not in circulation; in the US, this is also a separate category of mint products (a different finish than Proof, but still a single strike).

Note: Proof/BU/UNC are types of finish, not condition grades. Grading uses the Sheldon scale (1-70) and designations such as PF/PR (Proof) and MS (Mint State) for uncirculated coins; additional terms such as Cameo/Ultra Cameo refer to the strength of contrast.

What visual effects does a mirror stamp produce?

  • The fields (background) are as smooth as glass,
  • The relief (drawing) is matte/frosted, which provides a clear contrast (Cameo/Ultra Cameo).
  • The edges and details are very sharp thanks to multiple hammering.

An alternative is Reverse Proof - inverted contrast (matte fields, mirror relief).

How to recognize a Proof coin "in real life"?

  • Field mirror: the background acts like a mirror, often with a "black" sheen.
  • Matte relief: figures, inscriptions, and coat of arms are satin/matte.
  • Edge sharpness: Proof typically features sharp, "square" edges.
  • Packaging: Proof coins are usually encapsulated and packaged in boxes/certificates.

What coins are minted with a mirror stamp?

  • Collectible and commemorative coin series,
  • Proof versions of popular bullion coins (e.g., the silver American Eagle is available in a Proof version alongside the standard BU version),
  • Limited thematic editions with elaborate finishing techniques (e.g., reverse proof, enhanced).

Does a mirror stamp increase the value?

Usually yes – due to the more labor-intensive process, lower print runs, and higher visual quality. However, it is worth remembering that the market price depends on the print run, demand for the series, theme, and (in the case of graded copies) the Sheldon scale grade and Cameo/Ultra Cameo designations.

How is the quality of Proof coins assessed?

  • Finish: Proof / Reverse Proof / (Ultra) Cameo - description of contrast and type of finish.
  • Grading (condition): Sheldon scale 1-70 used by NGC/PCGS; for Proof coins, PF/PR + note is used (e.g., PF70), for "circulated" coins, MS (e.g., MS69).

Important: "Proof," "BU," and "UNC" are not independent "grades" on the 1-70 scale—they describe how the coin was minted, not its condition after minting.

How to care for mirror coins?

  • Do not touch the fields with your fingers—use cotton/nitrile gloves.
  • Store in capsules and in a dry place; avoid wiping (the mirror scratches easily).
  • Be careful with photography—mirrored fields "catch" dust and fingerprints; use a blower bulb before taking a photo.

Common misconceptions (and their corrections)

  • "Proof/BU/UNC are grading standards" → No. These are types of finish. Grading = Sheldon scale and PF/MS/SP markings, etc.
  • "BU has a mirror like Proof" → BU is a single strike and no selective matting; the mirror fields (if present) are usually a "prooflike" effect, not true Proof.
  • "Every investment coin is Proof" → No. Most bullion coins are BU; Proof coins are usually collector's versions of the same coin.

Summary

Proof coins are synonymous with the highest standards of minting: polished blanks and dies, selective matting of the relief, and at least double striking for spectacular contrast and micro-details. They are the perfect choice for those who value aesthetics, limited editions, and collectible coins.

This information is of a general nature only and should not be treated as investment advice within the meaning of applicable law. Investing in precious metals, among other things, may involve risk. Before making any investment decisions, it is recommended that you consult a financial advisor for an individual assessment of your investment options.

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