Alright guys, I have a really basic question. I have read several items on this, and am not clear on an important detail. Regarding Morgan dies - did the basining process make the die's fields convex or concave ? As far as I can tell, it made them concave - thus the coins' field was slightly convex. But I am not at all sure. Also... what other coin type dies received basining treatment ?
The dies were slightly concave. All basining is is another word for polishing. So just about any coin that can be found PL, the dies were basined.
Thanks ! I've been reading Van Allen / Mallis "Encyclopedia of Morgan and Peace Dollars" - an awesome piece of work in more ways than one - and that's what got me off on this. One of the net effects of basining was the Proof-like effect. But was that the intent, or a side effect ? VAM states* that before 1921, all Morgan dies were individually basined at each mint (some mints were better than others). This gave better definition between devices and field such that the design would be optimally brought up with a minimum of striking pressure. Was that the main reason for basining - to create a concave field to improve strike ? * p. 472, 4th edition
More a side effect than anything else. They weren't trying to produce Proof Like coins, they were just trying to do a good job. Well, they (the authors) are supposed to be the experts, but think about the process of striking a coin combined with the explanation you quoted above. Basining makes the field area of the dies slightly concave. So if the field area is slightly concave then that means that less metal will be pushed up into the devices than if the field area of the dies were left flat now doesn't it - just common sense. That seems to be contradictory to the explanation the book gives. There was a reason why each mint basined the dies. All the dies were actually made at the Philly mint and then shipped to the branch mints. But Philly didn't finish the dies, Philly left the final polishing and the placing of the mint marks to the branch mints. So the branch mints that polished the dies, and yet still left them as close to flat as possible were the mints that produced the best struck coins. The branch mints that got slightly carried away with the polishing and left the dies overly concave produced coins that were not as well struck. But yet the polishing did produce coins with Proof Like quality from all the mints. Back then, all the dies were prepared that way. You can find coins of any denomination of Proof Like quality.
My understanding is that they were mostly making them flat. They used a bowl shaped means of polishing so they should be slightly convex. No?
clad - if you use a bowl shaped polisher on a flat surface - what's the likely effect on the flat surface ? Or in another way of thinking - stick a bowl into the sand - you get a hole in the sand, not a bump.
I beg to differ with the statement that mint marks were added to the dies at the branch mints. With few exceptions, they were added to the dies at Philly prior to shipping to the branch mints.
I'm not sure - yet. I was pondering all this before starting this thread. We've settled that the dies were concave. Tell me if this makes any sense... If a die is concave, then as the press comes down, the edge of the die contacts the planchet's rim first, before the inner parts of the die. This exerts pressure first on the rim. As the die continues its travel toward the planchet, it progressively increases pressure toward the center of the coin. That means that, at any instant throughout the strike, the outer part of the planchet is always under more pressure than the center. At any instant, there is a pressure gradient - greater at the outside (rim), decreasing toward the center. Here's the key - all materials flow from high pressure to low pressure. Water in a pipe, winds blowing, or metal being pushed around. So the bottom line is this - basining the dies means that metal on the surface of the planchet will move radially inward toward the devices, away from the fields. It's a way of funneling metal from the outer fields toward the inner devices. The concave surface acts like a funnel. A flat die would just press straight down on the fields. Material coming up into the device cavity would be mostly metal directly under the device. If there's anything to this, it would explain why we see so many circular die cracks near the rim of Morgans. The die cracks are where the pressure was greatest. Perhaps it also explains these "radial flow die lines" I've heard about, which contribute to the famous Morgan cartwheel effect. What do you guys think ?
Pretty good assesment to me. The flow described, coupled with a wider die gap tolerance, is the reason that many of the N.O. Morgans have little hair detail over the ear. Hmmmm.... that would be pretty much the center of the coin, eh ? You got to love Mr. Bowers.
OK, think about what you just said - now think about how the rim is formed. The die doesn't even touch the edge of the planchet, the edge of the planchet is encased by the collar. The rim is formed last, just like the high points of the coin as the metal is pushed up, from the fields, into the die. Metal flows inward and outward both at the same time. Why ? Because you have 2 high areas to fill - 1 being the rim and the other being the center of the coin (devices). The greatest pressure is actually exerted midway across the radius of the planchet. That's because the planchet is basically flat except for the upset edge. The only extra metal there is in the planchet comes from the area of the planchet that will become the fields of the coin. It is this extra metal that is pushed outwards to fill the collar and form the rim, and at the same time it is pushed inwards to fill the recesses of the dies forming the devices.
Dies are slightly convex. They come together in the center first and then as the dies come closer the metal flows OUTWARD radially from the center toward the edge. (Actually it isn't quite in the center because normally the center of the die has an incused design there, so it actually make contact around the edge of the central devices. Due to the upset rim of the planchet they may also make contact there but would not receive as much pressure there until later in the strike when the upset material is used to fill in the rim of the coin.) This is why weak strikes show weakness in the high points of the design and around the periphery and a weak edge. If the dies were concave all the metal flow would be toward the center, the areas around the edge would strike up first and the central devices last. Even weak strikes would show sharp details around the rim and most likely a strong edge.
I beg to disagree again. The Denver Mint now produces it's own dies as well as some for the San Francisco Mint. This information is available on the US Mint web site if you care to check it out.
I'll go along with your theory - to a point. I agree metal will flow from the fields to fill the voids in the dies at the raised central devices. But as soon as those voids are filled (i.e., when the coin becomes fully struck) the metal starts flowing out (radially from the center). Not necessarily. A die (or any material for that matter) will crack when the stresses exceed the compressive or tensile strength of the material. It is not so much the "pressure" exerted as it is the stresses induced in the dies. Around the edges of the dies there is nothing to resist lateral forces (in this case "outward" forces). Sharp transitions (e.g., star tips in a die) are usually areas of high stresses. (For example, cracks in concrete, masonry and drywall typically begin at a sharp corner such as a window or door opening.) So, while other areas of the die may be experiencing the same "pressure" it will be the area where the steel is overstressed that will crack. Remember the old saying "A chain is only as strong as its weakest link"? The same applies with a coin die.
In Bowers book on Morgan Dollars he states on page 37 with regard to dies "If intended to be shipped to a branch mint, a mintmark was added to the reverse".
Thank you (all). As a novice, this type of information is valuable. I had to make a lot of drawings to fully understand. Somewhere I have read that a planchet grows in diameter after being struck; wouldn't this explain where the excess metal flows. Please excuse me for my ignorance, but I'm in the learning mode and have to come up with some of my own theories.
Also, in "From Mine to Mint", (Roger Burdette)probably the most extensive publication on 19th century coin making processes, he states on page 385, "All working dies for circulating coinage were made at the Philadelphia Mint in the die shop.... Addition of mint marks was also the exclusive prevue (sic) of the engraving department."
Not after, while it is being struck. The planchet starts off slightly smaller in diameter than the finished coin. As the dies are compressing it the metal tries to move away frme the compressing dies and that means radially outward away from the center (becoming larger in diameter) until it runs into the collar at which point it starts going up and down eventually filling the rim area of the coin. The inside diameter of the collar is the same as the finished coin.
As an example of a coin that was struck with Working Dies that were heavily basined, I post an 1921 High Relief Dollar that I own (my Avatar Image). This coin--especially on the Obverse--exhibits an extreme curvature in the field from the inner Rim to the Portrait; the Reverse also exhibits this curvature, but to a lesser degree. deFrancisci's design called for ALL Peace dollars to be struck in high relief, but because of poor results and early die failure, the design for 1922-1935 production coinage was modified to be in low relief. From Burdette's A Guide Book of Peace Dollars (Ch. 3, Pg. 42) "After experience in striking silver dollar, Mint reports relief too great and distribution of areas brings highest relief on each side in center of coin and to attempt to drive the metal into this part of design necessarily brings fin to outer edges and breaks die. Dies can be made to stand only about one hundred tons to square inch. The design is so distributed in circle that in making coin the metal is drawn away from the top and bottom and driven laterally to sides of coin resulting in decided difference in thickness which mars appearance of finished coin and interferes with stacking." The lighting I used was intended to show the highlights of the varying depth of the field curvature; the coin in hand is much more of a testament to the quoted citation. You will note the more pronounced field curvature at the bottom Obverse, and the Fin at approximately K8. Coins that exhibit the Finning were struck earlier in the coinage run before die failure(s) caused the Mint to reduce the striking pressure; the result being most of the run yielded coins with weak definition on the center of the Portrait. My coin, according to the illustrations and text description on pages 184 & 185 of Burdette's book, would be classified as a "very well-struck circulation coin".
