Strike-Through (STT)

A strike-through error occurs when a foreign object is caught between a die and the planchet at the moment of striking. The object prevents the die from fully impressing the design into the coin's surface in the area it occupies, leaving an incuse impression of the foreign object — or a blank, design-free depression — on the finished coin. Strike-throughs have been documented with an extraordinary variety of foreign materials: grease, cloth fibers, wire, metal fragments, staples, paper, tape, plastic, feathers, and even insects.

The term "strike-through" encompasses a broad family of errors united by a single mechanism — something was between the die and the planchet that should not have been there. The visual result varies dramatically depending on the material, size, and position of the foreign object.

How Does It Happen?

The minting environment is a high-speed industrial operation. Presses operate at 750 to 850 strikes per minute, planchets are fed and ejected by automated mechanisms, and dies are lubricated to prevent adhesion. Within this environment, foreign material can reach the striking surface through several pathways:

• Grease and lubricant accumulation: Dies are lubricated to extend their service life and prevent struck coins from adhering. Excess grease or lubricant can accumulate in the die's recessed areas (which produce the raised design on the coin). When these recesses fill with grease, the design cannot transfer to the planchet. This is the most common type of strike-through, known as a grease-filled die or grease strike-through.
• Cloth and textile fibers: Pieces of cloth, thread, or fiber from cleaning rags, gloves, or industrial wipes can land on the die face or planchet. The fiber is pressed into the coin's surface during striking, leaving a linear or curved impression.
• Metal fragments: Small pieces of metal — from planchet edges, die chips, or press components — can fall onto the die or planchet. These produce sharp, defined impressions in the coin's surface.
• Wire and staples: Wire from planchet shipping containers or binding materials occasionally enters the press. Wire strike-throughs leave distinctive thin, curved or straight-line impressions.
• Environmental debris: In rare cases, organic material such as feathers, insect parts, or plant matter has been documented in the striking chamber.

Once the foreign object is in position, the press cycle proceeds normally. The dies close with full force, and the object is squeezed between the die and planchet. The die impresses the design everywhere except where the object blocked it. The object itself is usually expelled after the strike (pushed out by the ejection mechanism), though occasionally it remains embedded in the coin's surface.

How to Identify a Strike-Through

Strike-through errors are identified by the impression left by the foreign material:

• Incuse impression in the design: An area of the coin's surface shows a depression, void, or foreign-object outline where the design is absent or incomplete. The surrounding design is normal.
• Object-specific shape: The impression matches the shape of the foreign object. Thread strike-throughs show a linear or curved threadlike impression. Wire strike-throughs show a thin metallic line. Grease strike-throughs show a smooth, filled-in area.
• Smooth or textured depression: Depending on the material, the impression may be smooth (grease, plastic) or show surface texture (cloth weave, metal grain).
• Design absence, not damage: The missing design in a strike-through area was never struck — the die could not reach the planchet. This is different from post-strike damage where design was struck but later removed. A strike-through shows smooth, original-surface metal in the depression; post-strike damage shows scratches, tooling marks, or rough metal.
• Single-sided: The strike-through affects only the side where the foreign object was positioned. The opposite side of the coin is typically normal (unless foreign material was present on both dies simultaneously).

Common Strike-Through Types

Grease-Filled Die: The Most Common Strike-Through

Grease-filled die errors deserve special attention because they are by far the most common form of strike-through. The die's recessed areas gradually fill with lubricant during a production run. As grease accumulates, it prevents design transfer to the planchet. The result is a coin with portions of the design smoothly filled in or missing entirely.

Common grease-filled die presentations:

• Partial date: One or more digits of the date are filled or weak because grease accumulated in the date area of the die
• Missing letters: Individual letters in legends (LIBERTY, IN GOD WE TRUST, E PLURIBUS UNUM) are absent or ghostly
• Featureless portrait: Portions of the main design element (Lincoln's hair, Washington's profile) are smoothed away

Grease-filled die errors range from minor (a single weak letter) to dramatic (virtually the entire design missing from one side). The more complete the design loss, the more valuable the error.

Notable Examples

Struck Through Cloth

Cloth strike-throughs are prized for their distinctive appearance: the weave pattern of the fabric is preserved in the coin's surface, creating a textured, grid-like impression. Large cloth strike-throughs that cover a significant portion of the coin's surface are particularly valuable and visually striking. The cloth texture is unmistakable under magnification.

Struck Through Wire and Staples

Wire strike-throughs produce thin, raised or incuse lines across the coin's surface. The wire's circular cross-section creates a distinctive rounded channel. Staple strike-throughs are rarer and show the characteristic U-shape of a wire staple impressed into the metal.

Struck Through Feathers

Among the most unusual and collectible strike-throughs are those involving feathers. The delicate barb structure of a feather is preserved in the coin's surface with remarkable fidelity, producing an organic, highly detailed impression. Feather strike-throughs are rare enough that individual specimens are well-known within the error community.

"Blank" Coins from Extreme Grease Fill

When grease fills virtually all of a die's recessed areas, the resulting coin shows almost no design — just a smooth, blank disc with faint traces of the highest-relief design points. These extreme grease-filled die errors are sometimes mistaken for unstruck planchets, but they show several distinguishing characteristics: they have a full rim (the collar still contained them), they exhibit faint design traces at the highest points, and their weight matches a struck coin rather than a planchet.

Collecting Tips

• Material rarity drives value: Grease-filled die errors are common and affordable. Cloth, wire, and metal fragment strike-throughs are progressively scarcer and more valuable. Organic material strike-throughs (feathers, insects) are rare and command premium prices.
• Size and visibility matter: A large strike-through that covers 30% or more of the coin's surface is worth significantly more than a small, barely visible impression. The most desirable examples show both a large impression and identifiable foreign-object detail.
• Design preservation adds value: A strike-through that leaves the date, mint mark, and primary design elements visible is more valuable than one that obscures attribution data. Collectors and grading services need to identify the coin's date and denomination.
• Object retained in the coin: Occasionally, the foreign object remains embedded in or attached to the coin after striking. These retained strike-throughs are rarer and more valuable than those where the object was expelled, because the object itself confirms the error's authenticity.
• PCGS and NGC attribution: Both major grading services attribute strike-throughs on holder labels and identify the material when possible (e.g., "Struck Through Cloth," "Struck Through Wire"). This attribution adds marketability and confidence.
• Examine with magnification: Many strike-throughs reveal their true nature only under a loupe or microscope. What looks like a smooth depression to the naked eye may show cloth weave, wire striations, or organic texture under 10x to 20x magnification.
• Not all missing design is a strike-through: Worn dies, die polishing, and weak strikes can also produce coins with reduced design detail. A genuine strike-through shows a defined boundary between the affected area and the surrounding normal design, and the affected area has a smooth, original surface rather than a worn or abraded one.

Related Error Types

• Capped Die (CPD) -- A struck coin adheres to the die and interposes between the die and subsequent planchets
• Die Clash (DCL) -- Dies strike each other without a planchet, transferring incuse design
• Off-Center Strike (OFC) -- Planchet mispositioned, producing partial design (not design blockage)
• Die Gouge (DGG) -- Damage to the die surface that produces a raised mark on every coin from that die
• Die Abrasion (DAB) -- Surface texture from die polishing, distinct from foreign-object impressions