What causes the Woodgrain toning on early Lincolns?
joefro
Posts: 1,872 ✭✭
When I started collecting a little over a year ago, I always ran when I saw one of these thinking it was the recovering surface of a previously cleaned coin. Now I see that these sell for "original surface" money and some people even enjoy the effect. So if some kind of chemical cleaning didn't do it, what can cause this type of "toning" effect?
Lincoln Cent & Libertad Collector
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Russ, NCNE
Yeah it's the metal mix. I have a couple.
That moose coin looks pretty cool
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USA Coin Album
by David W. Lange
San Francisco Mint Cents 1908-24
A professional numismatist has the privilege of seeing many more coins than the typical collector, including high-grade pieces that may be beyond his own collecting budget. While this may seem like a potential source of frustration, it’s actually a very rewarding and enlightening experience. Observations can be made over a period of years that simply aren’t possible when limited to one’s own collecting resources.
One thing I’ve noticed while examining uncirculated bronze coins produced by the San Francisco Mint from the onset of coinage there in 1908 through roughly 1924 is that they have some very distinctive features. These often enable one to identify them as ‘S’ Mint products before seeing the mintmark. Though the alloy used for United States cents was prescribed by law, there are peculiarities seemingly unique to cents made at San Francisco.
When entirely untoned, ‘S’ Mint bronze coins have a very pale, brassy color unlike that of the more reddish or coppery cents from the Philadelphia and Denver Mints. For the period described, however, ‘S’ Mint cents are seldom seen untoned. The only issues commonly encountered in that condition are the widely hoarded 1909-S cents, both with and without the designer’s initials "V.D.B." Subsequent dates through the mid-1920s are typically toned to various degrees, though many have survived with partial mint color.
Examples having just light toning often display a pattern of tan or light brown streaks across obverse and reverse, the so-called "woodgrain" pattern. This resulted from impurities in the alloy or concentrations of pure copper that did not properly blend with the 5% tin and zinc added to it. When these less-than-perfect ingots were rolled into strip, from which blanks would later be punched, the concentrations were flattened and stretched into the patterns seen on the finished coins. Invisible when first struck, these flaws appeared only after the coin was exposed to atmospheric agents that caused the copper concentrations to tone more quickly than the properly mixed portions of the planchet.
Woodgrain toning is commonly seen on ‘S’ Mint cents through 1923-24, after which time it is encountered only occasionally. Examination of the U. S. Mint Director’s annual reports for the period in question reveals that cent planchets were alternately made in-house (at the various mints) and purchased from outside vendors. After the mid-1920s, the U. S. Mint gradually phased out the production of both cent and nickel planchets in favor of ready-made ones, and this seems to have standardized the characteristics of planchets used at all the mint facilities.
Though most collectors favor bronze coins that are fully "red," I find this distinctive toning quite charming, and it further serves as an aid to authentication. I’ve never seen a 1909 cent from the Philadelphia Mint that was brassy and displayed woodgrain toning, so the presence of such distinctive features almost guarantees that a cent’s ‘S’ mintmark has not been added to a Philadelphia coin. This is true of both Indian and Lincoln cents.
As noted above, with the exception of 1909-S and 1909-S V.D.B. Lincolns, early ‘S’ cents are seldom seen with all their original color. Most have toned to brown or retain just partial mint red. One peculiarity I’ve noticed about all copper and bronze coins is that sharply struck pieces tend to tone down more readily than weakly struck ones. This is true regardless of date or mint, and I suspect that the relative degree of work-hardening experienced by the planchet determines its resistance to atmospheric toning. This phenomenon is not unique to ‘S’ Mint cents, but it is more critical with them due to their greater overall rarity. It extends even to the bronze one-centavo pieces made there between 1908-20 for use in the Philippine Islands. Having collected this series for years, I have almost never encountered a sharply struck coin having full mint color, while the well struck pieces I’ve owned were always brown or displayed light, woodgrain toning.
David W. Lange's column USA Coin Album appears monthly in Numismatist, the official publication of the American Numismatic Association.
<< <i>MrSpud is right. It is an aftereffect of the copper and tin/zinc not being fully mixed so it looks streaky. >>
The Mint purchased its bronze cent planchets from a private manufacturer before 1908, but for some reason when it decided to expand production to San Francisco it decided to begin mixing its own bronze at both mints.
The SF mint had a lot of trouble getting the 4% zinc and 1% tin to mix in properly, and whereever there was a significantly higher than 5% concentration of the alloy you had a small blob of brass within the bronze. Roll out the finished metal, and you get the woodgrain effect.
Tom DeLorey