Monday, August 25, 2008

Making World Coins

Part One - Making Silver Proof Collector Coins

The first of a two-part article on the coin minting process, here we explain just how those beautiful Silver Proof world coins you have in your collection came to be made.

When you look at the exquisite craftsmanship, mirrored fields and highly detailed frosted designs of Proof coins it's hard to imagine they are produced in what looks to be nothing more than a metalwork factory. But that is essentially what the mint's coin processing area is.

Various world mints have differing nuances when it comes to minting their Proof coins, however the overall process is generally the same. In this article we will explain the techniques used to create Royal Canadian Mint coins. There are other differences too when it comes to minting circulation coins as opposed to Proof coins, and we will look at circulation coin production in part two of this article.

The Coin Process
The metal used for the coins (Sterling Silver or Pure Silver) is melted down in a furnace at around 2000 degrees Fahrenheit. The metal is then cast into a bars roughly 1.5 inches (3.8cm) high, 5 inches (12.7cm) wide and 30 inches (76.2cm) long. The individual bars are then put through the Roughing Mill, which flattens them to around 0.3 inches (0.8cm) thick. These sheets are then heated for added strengthen and run through the Finishing Mill which flattens them to the desired thickness dependent on the coin being minted.

The flattened sheets are then put through the blanking machine which punches out circular blank "coin" disks. The left over remnants of the sheet, called Scissel, is melted down to be made into more silver bars.

The blanks are fed through a Rimming machine, which adds a raised edge and removes the rough edge caused by the blanking process. The idea of the rim is to enable the design of the coin to be transferred faultlessly at the time it is struck. Adding a rim to a coin is said to add 10-15 years to the coins life.

From there the blanks are placed in a Burnishing machine which is sort of like a huge washing machine full of steel beads, cleaning solution and water. The beads work as an abrasive to finely polish the blanks. The Burnishing procedure is repeated many times over and can take up to 6 hours for a "cycle" to be completed. Once burnishing is complete, the blanks are spread out individually and towel dried by hand to ensure that no scratching or water marks appear on the surface.

The blanks are then fed through another furnace to heat and strengthen them prior to being struck.

The Design Process
The design process starts simply with an idea or theme which is then realized as an image. The design can come from an original artwork or a photograph or a combination of the two. The Mint designer creates the coin image on computer to be submitted for approval from Mint officials. From there another computer program connected to an engraving machine gets to work making a rough engraving onto a large plaster disk. This engraving process creates the design as a negative image which is then used as a mold to create a positive plaster disk. The positive disk is then enhanced by hand by a sculptor and the finished disk is used to cast a negative in plaster, which is then used to case a positive cast in rubber. From the positive rubber mold they cast a negative in a hard epoxy which is placed on a Pentagraph machine. The Pentagraph is a reducing machine which traces the larger hard epoxy disk and creates a smaller brass replica 1 1/2 times the size of the original. The reduced reproduction process takes 36 hours to complete and the resulting negative brass template is given to an engraver to fine tune. This is also where the lettering such as denomination, year and country of issue is added to the coin design.

The negative brass template is then put back on the reducing machine for another 36 hours where a copy is traced in high-grade steel, 1 1/2 times smaller than the brass disk. This reduced copy is called a matrix and it is the same size as the coin to be struck. The matrix is then struck onto a block of steel creating a positive image called a punch and finally the punch is struck onto another piece of steel to create a negative image. This is called a die (also known as working die) and it will be used to strike the coins themselves. There are two dies for each coin; the bottom die (Anvil) usually produces the side of the coin known as the Reverse, while the top die (Hammer) produces the Obverse.

Still following along with all those negatives and positives? The making of coins is a complicated process but each part of the puzzle is important in creating something that will stand the test of time.

Note: Depending on where you are in the world the sides of the coins may be the other way around. For example, in the United States the Obverse (also known as the "front" or "tails") is the side that carries the theme or focus of the coin, such as a commemorative event, anniversary or public figure of importance, while the Reverse (also known as the "back" or "heads") usually carries the portrait of a past US president or the United States coat of arms. In Australia the Reverse of a coin is the theme side (front) and the Obverse is known as "heads" on account of the effigy of Queen Elizabeth II being on that side.

Bringing Coin and Design Together
There are two different presses that can be used for striking collector coins. The Automatic press is mainly used for non-precious metals such as Copper and Nickel, and the Manual Press is used for Silver, Gold and Platinum coins. As Proof coins are placed into the press by hand an average 8-hour shift will produce around 8000 coins. Compare this to the 15 million circulation coins struck in a day and you begin to see the special care taken to create these miniature works of art.

The Proof dies strike the coin simultaneously, two or three times to create the high quality impression you see in your Proof issues. Each Proof coin is then individually examined to check for blemishes and warping. Due to the highly polished fields of Proof coins and the high pressure used to strike them, the striking process can sometimes produce a "ripple" effect noticeable in the mirrored portion of the coin. If this happens the coin is rejected and sent back to the furnaces for re-melting.

The finished Silver Proof coins are encapsulated and in most cases enhanced by elegant packaging that creates an even more splendid display for the collector upon purchasing.

Silver bars after being flattened

Going through Blanking machine

Coin blanks in the Burnishing Machine

Blanks are towel-dried by hand

Computerized coin design

Computer etching on plaster disk

Epoxy disk on Pentagraph machine

Matrix being etched from Brass template

Proof coins are minted by hand

Coin blank ready to be struck

Finished coin still in press

Canada 2008 $1 Silver Proof
- Example of finished Silver Proof coin

Below is a video presentation of the Silver Proof collector coin minting process.

1 comment:

Australian Silver Coins said...

Very interesting. It certainly is a long and detailed process and not one I'd really considered before. I was unaware that in different parts of the world the sides of the coins are different (just to make things a little more confusing).