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How are bullion gold coins made?


RoughDog

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Does anyone know how the majority of the bullion gold coins are made?

From watching various videos my understanding is that a blank coin in placed in some form of press. 

The press imprints the image on the coin via pressure.  This works because gold is a very malleable metal.

What I don't understand is that lots of the bullion coins have a wet looking appearance to the main image on the coin which looks very different from the reeded edge.

The main image has a kind of poured of molten look.  How is this achieved?  Is the coin heated while being pressed or is there some form of second process to get this look?

 

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Do you mean proof coins?

The matt look to the raised areas?

It's done by sandblasting some areas of the die(stamp) and polishing others.  Proofs are usually stamped a number of times as well.

Normal coins are also machine stamped as well so the metal doesn't need to be soft or malleable.  Tremendous pressures can be attained when using hydraulic machinery.

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I was referring to bullion coins.

The reeded edge and background look different from the main image, the image has a glossier wet look.  Referring to queens beasts I have. 

Krugerrands being different as they have same single colour shade, look and feel to entire coin.

Silver coins such as lunar have this effect too.  Queeny is glossier than background.

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Logically, the different appearances of the finished coin are a combination of the contact between the blank and the die surfaces.

If you start off with two polished surfaces, you will end up with a totally shiny, polished coin. If one surface is matt, possibly caused by sand blasting etc, it will impart a matt surface to the coin.

The issue is how easily you end up with two polished surfaces to produce the "glossier wet look" to the coin's main relief features. To polish the blank would be easy, to polish the recessed part of the die that imprints the relief features, less easy, but possible.

To produce the matt areas of the coin would require the corresponding areas of the die to be "roughed up" in some way.

 

Profile picture with thanks to Carl Vernon

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4 minutes ago, Murph said:

Maybe it's the texture of the background that highlights the foreground smoothness with the Queen's beasts?

I've always thought the very shiny foregrounds on some bullion seem to lack detail.

Yes, you are right! The shiny foregrounds of bullion coins do lack detail when compared to the frosted foregrounds of proof coins which have been clearly struck many times.

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I can fully understand the point you are making about bullion coins because I’ve also wondered myself why some of them have matt backgrounds. Proof coins, of course, are completely distinguishable with their polished backgrounds. The Perth Mint, especially, love matt backgrounds. The Mexican Mint favour matt bullion coins. The Royal Mint like polished bullion coins.

Unfortunately, I don’t work for the Mints mentioned and can’t speak on their behalf but I’m certain @Murph and @sovereignsteve are right. The process is probably simpler than you think. The matt background is done by first sandblasting the engraved die and the polished interior image added to the sandblasted die afterwards.

E3F41156-7E8D-4DEB-B2EE-3502808721B8.jpeg

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