A Description of the Striking of a Matte Proof Cent - Dies to Coin
FlyingAl
Posts: 3,502 ✭✭✭✭✭
I recently asked a member here if they could describe the entire minting process of a matte proof cent, and then I wanted to know if I could. I had better not challenge someone to do something if I can't do it myself! Here goes!
Most information (nearly all) taken from Roger Burdette’s From Mine to Mint. This is a critical reason why books are so important in numismatics, because the internet couldn't have told me half of this. Buy the book before the coin! Many websites can contain incorrect info as well.
Die steel was chosen by the engraver of the mint, and often the quality of the die steel would result in better or worse dies, and as a result the finished coins could have a slightly different quality when they were produced. The quality of the steel would result in differing abilities to anneal and harden the dies correctly, and therefore the dies would last longer or shorter in the press and the coins would have detail differences based on if the die was hardened properly. The steel also affected how the dies responded to treatments such as polishing or sandblasting, which is particularly important for proof production.
Die steel was ordered from the United Kingdom up until around 1878. The two compositions of modern steels here closely show what was used in the early 1900s. These were approximations of steel from William Roberts-Austen, a British metallurgist, that he created in England as a result of the Royal Mint’s needs for better die steel during the 1880s.
The first steel is composed of 97.15% Iron, 1.5% Chromium, 1% Carbon, and 0.35% Manganese. It has an annealing temperature of 1,440 degrees Fahrenheit.
The second is composed of 94.75% Iron, 1% Chromium, 0.7% Carbon, 2% Manganese and 1.25% Molybdenum. It has an annealing temperature of 1,400 degrees Fahrenheit.
The engraver was responsible for making sure that all die steel was properly made and that it was good for use. The dies started as blocks of steel that were heated, and then hammered into a roughly cylindrical shape, and machined to the proper standards for die blanks.
These two dies steels were used to great success by the mints of the United States. The next step in the process is to create a model of the design, usually a plaster one, and create an electrotype of it. This would make it suitable for the reducing lathes in use to be able to take this electrotype and reduce it onto steel creating a master hub. This was a relief copy of the model, just to the correct size for coin production and without a date. Correct usage of this reducing lathe was critical and it changed the amount of manual re-engraving the engraver had to complete before the master hub was ready for use. This hub was then hardened and ready for use for die production.
The master hub was put into the upper position of a hydraulic press and it was then impressed into an annealed die blank. As a result, some of the design was transferred, but not all. This partly finished die was heated in an annealing furnace and then slowly cooled to a point where it could be impressed with a hub. The process then started over. Each annealing cycle took around four hours, and multiple cycles were needed for each die. The smaller the finished coin, the fewer the blows needed. After the die was completed, it was put into a cast iron box with charcoal to exclude the air. They were then rapidly cooled by water, leaving them extremely brittle. To fix this, the mint would then anneal the dies by heating them to a yellow color and letting them cool in a tank that was specially designed to create a hard die face but a softer shank to withstand shock. All dies were made at the Philadelphia mint.
This die was then often used as the master die. A date was punched into it, and the process above was repeated to create working hubs. These hubs then created working dies by using the same process.
Proof dies were identical to those used for circulation strikes, the only difference was that they received a post hubbing treatment. For matte proofs, this was a sandblasting of the dies before the die was tempered, leading to a dull surface. The mint chose this route (sandblasting rather than polishing) as the new dies had a curve to the fields (called radius), rather than the flat fields of earlier designs. The engraving department had no way to effectively polish the fields, so they elected to sandblast the dies.
Satin proof dies received no post production treatment, and sandblast proof gold was created by taking a satin proof coin and sandblasting it.
The metal received for minor coinage was purchased by the superintendent with approval from the director. The metal was then melted by the melter and refiner into ingots that were twenty three inches long, four and one eighth inches wide, and three quarters of an inch thick. These were transferred to the coining department where they were passed through a machine that reduced the size of an ingot to the correct width in about 15 passes. The flattened ingots then went to a blanking press where blanks were cut and then sent to be annealed. The blanks were then milled to give a raised rim and the blanks were ready for coinage. Those destined to be proofs were polished.
The polished blanks were sent to the medal room, where they were struck once on a hydraulic medal press. They were individually handled, and they were carefully inspected to ensure quality, and if they did not meet the standards they were rejected and melted. The finished proofs were then packaged and sent to the Cashier for sale.
Coin Photographer.
Comments
I'll give this one a title change and a bump, I feel some here may be interested in this.
Coin Photographer.
Very nice write up Buddy, I learned something!
Very interesting post @FlyingAl... I recall some of that from Roger's book - though it has been years since I read it. Good information, just what this forum needs - among the other good contributions of coin pictures etc.. Cheers, RickO
Great write up and Nice explanation.
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I can almost see the process. Thanks for sharing. Peace Roy
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Thanks for this info! I learned a lot more about the minting process than just matte proofs. @FlyingAl said:
How were satin proofs made if they didn't get any post production treatment?
Also, how'd you know to look in that book for that specific info?
Young Numismatist
Satin proofs still got the extra pressure of a hydraulic medal press. The dies were just normal dies like the ones used for circulation coins. The difference in how the coin appears is due to the extra pressure, new dies, and special care in handling them.
From Mine to Mint has everything that you could ever want to know about the mints and minting process. It’s everything the Red Book has, doesn’t cover, and then some. I knew to look in that book because I knew everything about the dies would be in there. The knowledge about striking had come from the boards and other books.
Coin Photographer.
Thanks. I forgot about other things like special care, extra pressure or planchet polishing that made proof coins special.
I think I might just have to buy that book!
Young Numismatist