Next Tuesday, 1146 coins from the Royal Australian Mint's Master Collection will be sold through Downies Australian Coin Auctions at Box Hill Town Hall in Melbourne.

The coins to be sold are known as production standard master coins, used by the mint for quality control during the production of circulating and collectable coins.

Here's how it works. Two coins are hand-picked from the first batch struck of every new series and retained as quality standards. One is kept on the factory floor for checking purposes, then destroyed after five years. The second master is marked in red and placed in the official mint archives. These are the ones that will be sold.

Master coins are not included in the official mintage figures, so some collectors may not even be aware of their existence. It's the first time any have been offered for public or private sale.

The coins date from 1986 to 2014. Auction estimates range from $25 to $60,000. They are being sold because the Mint is streamlining the manufacturing process, which includes reducing the number of coins kept in the archives.

"This regular review and audit of processes is vital to ensure items are not retained unnecessarily," says Royal Australian Mint chief executive Ross MacDiarmid.

"In effect, these coins are unique," he says. "They are the greatest among their equals."

The highest estimate at the sale is $60,000, for the 2012 Lucky Dragon gold master coin, weighing one kilogram. Its condition is described as proof-like. These coins retailed for about $92,000 at the time. The official mintage figure was 100, with as many as 90 sold.

The lowest pre-sale estimate value is $25, and is how much you could expect to pay for a 1990 one-cent master coin, one of the last required, as Paul Keating decided to delete the smaller denominations soon after. Millions of 1¢ coins were produced, but even the common ones are now gaining modestly in value, selling for 50¢ or more.

To read the complete article, see:
Mint's master sale has coin collectors excited (www.smh.com.au/money/investing/mints-master-sale-has-coin-collectors-excited-20150514-gh1fgx.html)