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by Andrew D.N. Andison, 22 Jul 1995
Recently I was privileged to go on a visit to the British Royal Mint in Llantrisant, a town a few miles north of Cardiff in Wales. There are only three or four visits per year with a maximum of 18 people on each one so if you ever get the chance to go make sure you take it. The visit lasted a full three and a half hours and was extremely comprehensive.
We were split into three groups of six and my group started in the smelting hall.
The bulk of this vast room was taken up with ingots of raw material (copper, zinc, tin, nickel and a variety of other metals) and long strips of finished alloys. The raw material was smelted in large furnaces and tested until the right mix of materials was produced. It was then poured into holding furnaces from which long bars were drawn off. The bars were roughly 15m long, 20cm wide, and 2cm thick. The bars were then passed through a grinding machine where the surface layer was stripped off--apparently in the 75% Cu 25% Ni alloy used for much of the world coins the copper tends to work its way to the surface. After grinding the bars go through a rolling press where they are reduced in thickness--a process that is repeated several times until they become thin wide strips rather to thick narrow bars. At the same time they are coiled up to save on space.
A further rolling press awaits the coils but unlike the previous ones this one flattens the strip to the exact thickness required for the intended coins. From this mill they go through the machine that punches out the blanks (or planchets as they are called in some places!). The blanks are the run through an edging machine that forces up the edge; the purpose of this being twofold--firstly it stops the blanks from sticking together, and secondly it means that the coining press has less work to do later on when it produces the rim.
That was the final stage of processing in the smelting hall so we followed the blanks into minting hall.
Before a blank ever sees a coining press it has to be "prepared". Firstly they are tipped into a furnace which burns of any impurities and also softens the metal. Then there are put into washing machines. It must be said that these washing machines are quite a bit larger than your average domestic model. Not only to they cope with loads greater than 11lb but the various wash cycles include sulphuric acid. After a quick blow dry the blank are then coated with a very light layer of mineral oil to help them through the mechanical minting processes.
One more stage awaits the blanks before being fed into the coin presses and that is the edging machine, somewhat similar to the one in the smelting hall. It is on this machine that edge lettering, such as on the current UK pound coin, is added. The centres of bimetallic coins have a groove cut into the edges so that the outers key into it when being struck and stop the two parts separating.
The next stage is the coining press.
The collars used for striking the coins are arranged in a circle and this circle moves round in steps so that each collar in turn stops below the dies. In one of the presses bimetallic Argentinian one peso coins were being minted. The outers were fed into the collars via a feeder. As the collars moved round the inners were fed in via another feeder. The collars with the two parts stepped round until they were below the dies. A quick thump and the two 'worthless' bits of metal became worth 1 peso. A step later and the coins was ejected into a barrel along with the thousands of others. The collars themselves are used to give the edge to the coin. In the case of the UK pound coin they put the milling over the top of the previously impressed lettering.
There are two rows of coining presses thumping away producing coins for a variety of countries. The only British coin that I could see being made was the 1 penny. The ones being produced were dated 1994 and when I asked why (it was after all the middle of 1995) I was told that they still had a stock of working dies dated 1994 and they would keep using them until they ran out. Also the treasury didn't really care what date was on coins as long as the mint produced the quantity they required on time and at the agreed price. I was puzzled by the presses that had bits of paper stuck on the front saying "reverse strike". Apparently these are to remind the operators that the obverse/reverse alignment is 180 degrees, rather than the more normal 0 degrees.
After being struck the coins were bagged, rolled, boxed, crated and counted and ready for despatch to the purchaser.
In another hall medals and commemoratives were being struck. The presses used to make these were slower than the ones used to make the circulating coins. The most obvious difference was that the presses would often strike the same piece several times. In the case of the current British 2 pound coin, commemorating 50 years since the end of the war, the press was mechanically striking each piece twice. Medals on the other hand were being struck very carefully with the operator hand feeding the press and making an individual strike. Firstly, worn dies would be used to make the initial strike. This would produce the bust of the queen as well as some lettering. Secondly, the first strikes would be restruck using newer dies. This would add more detail to the queen's bust as well as producing most of the lettering. Thirdly, the second strikes would be restruck with new dies to produce the finished product. The dies used for the first and second strikes are not damaged, they have been polished so often that much of the design is polished away.
Die production was the next part of our visit and we were taken to the room were most dies start there life. The initial stage is where the customer submits his or her designs which are translated into practical coin designs. A large plaster cast of the piece is created and from this a metal electrotype is created. The design at this stage is raised in the same way as the finished product. The electrotype is then put on a reducing machine and a matrix created. From this matrix a master punch is produced by squeezing the two together. The design on the master punch my be subject to some final adjustment--like adding the date! The master punch is incuse and retrograde like the coining dies. By another squeezing process the working punch is created. I think this is what is called the hub in the US. From the working punch the working dies are produced and from them the coins themselves. The working punch can produce many hundreds of working dies but in the event of it wearing out a new one can be made from the master punch. In theory the only time that varieties would be produced is when the matrix has to be used again to produce a new master punch.
There was a visit to the mint's museum and this was a collection of many, many thousands of coins, dies and other minting related items. The museum undoubtedly holds the best collection in the world of British "milled" coins. We were shown various examples of the coins in the collection--1933 penny, Edward VIII patterns, that sort of thing!--as well as the trial pieces for the new smaller 50p and the bimetallic 2 pound coin. I have to admit that despite its rarity the 1933 penny looked just like a 1932 or 1934 penny but with a different date.
The three groups met up again for the life-saving tea and biscuits and there was much discussion about all things to do with coinage and minting. Some in the party expressed the view that they hated the changes that have happened to the British coinage over the years while others found the changes refreshing and in direct contrast to some countries that had tired old designs that had been around for far too long. I think that was a reference to US coinage. After tea it was time to go. The staff who had acted as our guided were thanked for the excellent job they did--it can't be easy answering questions at the rate we were asking them.
Footnote:
Security was tight at the gatehouse and you had to leave all your coins in a little locker before going in. You were liable to be searched on the way out which was a great disincentive to take home any free samples. Throughout the visit you would keep finding coins on the floor but had to resist your natural instincts and leave them there. The one bit of the mint we weren't allowed in was the precious metal facility in the centre. This was like a mini-mint with all the processes done in the other building being done on a smaller scale.
Quality was maintained to a very high standard everywhere in the mint. There seemed to be checking done at every stage with some of it done by eye and some done by mechanical and optical machinery. After the blanks had come out of the washing process we had to put anything we touched straight into the scrap bins. Apparently it upsets customers when coins are delivered with fingerprints all over them! If any of the barrels of coins are considered suspect in any way they are put into quarantine. They are then checked and if found to be ok are passed on to the bagging machine, but if they are not ok then they go straight back to the melting pot. Indeed the whole process was like a tournament with each stage being a contest between the the product and the quality inspectors. At any time the quality inspectors could win and send the product back to square one.
All in all the day ranked as one of the highlights of my year (if not my decade!) and I would like to express my thanks to all those involved in organising it.
Andrew D.N. Andison
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