Improper Annealing (IAN)
Improper Annealing occurs when a coin's blank is not heat-treated correctly during annealing, the step that softens the metal after the strip has been rolled and the blanks punched from it. Rolling hardens the metal, and annealing restores the softness the blank needs to take a design. On copper-nickel and copper-nickel clad coins, an annealing failure shows up mainly as abnormal surface color: a copper-red, brown, black or gray layer that can flake away.
How Does It Happen?
After metal strip is rolled to the correct thickness and blanks are punched from it, the blanks are annealed. The U.S. Mint describes heating them in a furnace at up to about 1,600 degrees Fahrenheit in an oxygen-free atmosphere, which keeps the metal from tarnishing (search). After the furnace, the blanks are quenched, washed and dried, then run through the upsetting mill that raises their rim.
According to the explanation Mint technical staff gave error researchers, reported by Error-Ref, the discoloration comes from one of two failures, or both together:
- Too much heat: the blanks are exposed to heat for too long.
- Loss of the protective atmosphere: the furnace fails to keep its oxygen-depleted atmosphere.
Either way, copper and nickel atoms in the alloy migrate to the blank's surface and separate into fairly pure layers. Because the copper-nickel alloy holds about three times as much copper as nickel, copper reaches the surface more strongly, which gives the reddish look. The copper layer is brittle and can flake off, exposing the oxidized blank underneath (Error-Ref).
On clad coins the alloy involved is the copper-nickel outer layer itself, which separates in the furnace, not copper rising from the pure copper core.
How to Identify Improper Annealing
- Surface color anomaly: Error-Ref lists copper, red, black, brown and gray. The color can cover the whole coin or only part of it, and the copper can range from a slight tinge to a thick coating.
- Flaking or peeling surface: In heavier cases the brittle copper layer peels or flakes, exposing darker oxidized metal beneath (Error-Ref).
- Mint luster: A coin struck on an improperly annealed blank still came off the dies with its luster. Mike Diamond has noted that a discolored coin with no mint luster points instead to environmental discoloration (search).
- Check the edge: Fred Weinberg has advised that on coins without reeding it is the edge, not the rim, that tells. Because ejection from the collar scrapes the color off, a genuine mis-annealed coin shows an edge that differs in color from its faces (search).
Improper Annealing vs. Environmental Discoloration
| Feature | Improper Annealing | Environmental Discoloration |
|---|---|---|
| Cause | Furnace failure before striking | Storage, soil, chemicals or heat after the coin left the Mint |
| Color | Copper, red, brown, black or gray, from a tinge to a thick coat | Varies; often uneven, with corrosion |
| Luster | Present under the color | Often lost |
| Surface | Brittle copper layer may flake | No separated copper layer |
| Edge (plain-edge coins) | Differs from the faces, scraped by the collar | Usually discolored along with the faces |
Notable Examples
"Black Beauty" Jefferson Nickels
"Black Beauty" is a collector nickname for very dark Jefferson nickels attributed to improper annealing. The 1959 Philadelphia nickel is the date most associated with the name, and collectors apply it to other dates of the period too (search). The color is often dark gray rather than truly black. A dark nickel alone does not confirm the error, since soil and environmental damage can darken nickels too.
Jefferson Nickels Generally
Error-Ref's examples are all nickels: a 1962 nickel with peeling copper over part of the obverse, a 1992-D with a heavy copper coating on both faces, and a 2005-D with the Bison reverse.
Clad Coin Improper Annealing (Dimes, Quarters, Half Dollars)
Error-Ref describes the error on copper-nickel clad coins as well as on solid copper-nickel nickels. On a clad dime, quarter or half dollar, the coin that should look silver-toned instead shows the copper, brown, black or gray layer of the separated alloy.
A Note on Attribution
The older collector names "copper wash" and "sintered plating" grew out of guesses about the cause. Once Mint staff identified annealing as the cause, the major grading services generally moved to calling these "improper annealing" errors (Error-Ref). Collector posts report that labels have differed by service, with NGC using "Improperly Annealed Planchet," PCGS "Sintered Planchet" and ANACS "Improperly Mixed Alloy" (search). These labels describe the same error.
Collecting Tips
- Clad coins and nickels are where it shows: on copper-nickel and clad coins the wrong color is obvious, a reddish, brown or dark coin that should be silver-toned.
- Look for flaking: When evaluating a coin with unusual coloration, examine the surface under magnification for a brittle, flaking copper layer.
- Color must be original: Do not confuse environmental toning or damage with annealing discoloration. Annealing color forms in the furnace, before the coin is struck. A coin that was normal when new and later turned dark is toned or damaged, not improperly annealed. Check for luster and, on plain-edge coins, the edge.
- Combine with provenance when possible: Coins found in original mint sets or uncirculated rolls carry more credibility than loose coins, because the packaging makes later darkening less likely.
- Grading service attribution: Grading services note improper annealing on the holder label, which separates the error from environmental damage for future buyers.