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Junior's Numismatic Lesson of the Day: Die Lapping of Bust Coins
JrGMan2004
Posts: 7,557 ✭
Die Lapping was a common procedure in the early days of the mint. Because there was a lot of work and time put into making the working dies, it was often easier just to lap the dies to remove defects and problems. Die lapping reworked the die by 'lapping' it on a surface plate with a fine pumice or rottenstone with some cutting fluid. This affected the highest point of the die, the fields. Die lapping was good for removing clash marks as well as to remove small die cracks, at least temporarily. Though dies were often covered with wax to help prevent rusting, dies still sometimes started to rust leaving pits. Sometimes die lapping was succesful in removing the rust pits left behind. Sometimes in this case, the last coins struck will not show signs of the rust pits that were evident on earlier die states. It also worked well to remove orange peeling from the fields. Many dies were able to return to service after lapping, some dies being lapped a half-dozen times or more before being retired, and producing coins that are very proof-like, at least for the first few strikings.
Die lapping is known to have caused loss of shallow details, such as the stems on berries and the shafts of the arrowheads, because it takes metal off the fields. Die lapping, also can cause loss of detail in Ms. Liberty's curls. It also causes the stars to become slightly smaller, and also move apart, after being lapped. It has the same effect on the dentils. A pair of dentils that may have touched in an early die state, may no longer touch after the die has been lapped and also somewhat due to die erosion.
Die lapping is known to have caused loss of shallow details, such as the stems on berries and the shafts of the arrowheads, because it takes metal off the fields. Die lapping, also can cause loss of detail in Ms. Liberty's curls. It also causes the stars to become slightly smaller, and also move apart, after being lapped. It has the same effect on the dentils. A pair of dentils that may have touched in an early die state, may no longer touch after the die has been lapped and also somewhat due to die erosion.
-George
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George, excellent summary. Keep it coming!
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Tbig
Great lessons for us all.
Some additions: All working dies on bust coins were lapped before usage to grind down the displaced metal from the punching of the stars, letters, numerals. Sometimes the lapping was excessive, causing weak lettering with missing serifs on some varieties.
Craig Sholley (Rittenhouse) has determined that some of the pitting thought to have been caused by rust is actually spalling, deterioration from usage. With halves, dies were usually in work continuously, not having a chance to rust. The spalling increases on these dies with usage, unless lapped.
Bill
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Liberty: Parent of Science & Industry
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Lapping was generally done with a lap - a slighlty curved plate or disk made of a soft metal such as zinc. The plate was curved to maintain the curvature (or basin) of the die as destroying the curvature would affect strike. A lap typically has shallow grooves to hold the lapping compounds, which were made from finely ground minerals such as iron oxide (jeweler's rouge), chromium oxide, aluminum oxide (bauxite) or diamond dust mixed with tallow, oil or water. Pumice and rottenstone are polishing agents typically used in woodworking not metal working - they are quite abrasive. Lapping is essentially the same as polishing although the former implies a more aggressive metal removal.
As noted, lapping at the early Mint (pre-1840) was a very common practice to extend the useful life of a die. Lacking the process to hub full dies, die production was tedious, time-consuming and expensive. Dies were frequently lapped multiple times, often more than seems prudent - several early coppers and bust coinage shows extremely heavy lapping as evidenced by missing detail and mushy strike. One early cent (forget the Sheldon number) had its reverse nearly erased by overly aggressive lapping.
As Nysoto mentioned, most of the pitting seen on early coinage is the result of stress induced "chip out" or spalling in the die - the dies were chipping out due to the stress of repeated pounding. This can be easily seen to be the case as the pitting generally grows worse in later states. How can a die continue to rust while in use? Also, steel does not rust instanaeously, a pit will take quite a while to develop. I've had some unprotected die steel from the 1850s in my unheated garage for 6 years and it is just beginning to develop a nice fine coating or rust.
Lapping is still fairly common today to remove clashing and other surface defects.
Truth be told, most of my information came from the Logan and McCloskey book on Half-Dimes... Half-Dimes didn't see as much use as Half-Dimes did, and there's certainly several examples of Reverses that have been used in multiple years, and even remarriages where a reverse used with the obverse of one year, then was used with the obverse of the next, and then was struck with an obverse of the previous year...
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<< <i>Can someone explain the difference between "die lapping" and "die polishing" - or is it the same thing?? >>
i wouldn't consider them quite the same thing. ie proof dies are "polished" not lapped, as that would obviously degrade the quality of the dies, which is counter to the intent. just my 2c worth contribution to a great thread.
K S
<< <i>When I was at the ANA, board member "Dahlonega" showed me two gold coins of the same date and MM. One was a coin that had pits from rust and overt clash marks. The other, from the same die, had lack of some of the fine details but a nice smooth appearance. I believe a stem was no longer visible. He postulated that the first coin was from the die before it was lapped, and the second was soon after the die was lapped. It was a pretty cool! >>
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I learned something today!......See ya at FUN
Brian
Specializing in 1854 and 1855 large FE patterns
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-Randy Newman