Stack graduated from the University of Akron (Ohio) in history and philosophy, and joined the family firm in 1973 with a special enthusiasm for English hammered coinage.
Whilst with the firm, he formed major collections of French Ecus, Five-Franc pieces and Ecus d'Or, and his collection of Celtic and Anglo-Saxon coins ranks as one of the greatest ever brought together.
But it's impossible to cover all of these collections, and in this case we're going to take a look at a collection one step removed from coins in the sense of currency.
That is Stack's collection of portrait medals, specifically Renaissance portrait medals. He felt that the market was being overlooked and that there was a happy coincidence of an interesting topic and investment opportunity.
 The crucified Christ, as depicted on the Hans Reinhart medal |
However, Stack put together the collection in a partnership and when he left the family firm this dissolved. The collection had to be divided, and with some reluctance Stack agreed that it must be sold. This seemed the only way to divide it fairly.
He elected to offer the pieces with no reserve prices, to encourage others into the hobby. He remains an enthusiastic collector himself.
The honour fell to Morton and Eden in December 2009. Tom Eden, expert in charge, said: "A sale of this significance being sold without reserve has no parallels and offers huge opportunities to collectors, dealers and institutional buyers.
"Renaissance medals have always fascinated academics but have generally not been taken seriously by top-end collectors.
"They are important objects which often furnish us with images of individuals whose portraits are otherwise unknown and they display, in a very personal way, the changes in portraiture and art styles from the 15th century onwards.
"They are an important adjunct to painting on the one hand and sculpture on the other".
 The incredibly detailed Mary I gold medal by da Trezzo |
The collection included four exceptional bronze medals by Pisanello who is generally credited as the inventor of the modern medal in the late 1430s.
These depict Leonello d'Este, Marquess of Ferrara, Vittorino da Feltre, the humanist, Alfonso V, King of Aragon and Sicily and Don Inigo d'Avalos, Grand Chamberlain to Alfonso V.
From later that century came a bronze medal of the humanist philosopher Giovanni Pico della Miradola attributed to Niccolo Spinelli, called Fiorentino, circa 1485, thought to be the finest known.
This medal was sold by Sotheby's in Zurich in 1974, when it realised CHF 65,000, at the time a world record price for a medal.
Then there was Albrecht Durer's silver medal of Emperor Charles V, struck in 1521, commissioned by the City of Nuremberg in anticipation of the emperor's visit following his coronation in Aachen in the previous year.
 Peace makes a stand on the reverse of the Mary Tudor medal |
It is one of eleven known specimens in silver of which this and one other are the only examples outside a museum.
A piece with loftier intentions was Hans Reinhart's masterpiece, the silver Trinity Medal of 1544, issued by Maurice, Elector of Saxony, in an attempt at reconciliation between the Protestant and Catholic churches.
But the most coveted lot was a gold medal of Mary Tudor by Jacopo da Trezzo formerly in the Rothschild and Gaines collections and one of only two known.
The medal was made in 1554, the year of her marriage to the future Philip II of Spain and was once on display at the National Gallery, London, as part of the exhibition Renaissance Faces.
It bears a strong resemblance to the famous portrait of Mary by Antonis Mor, done at a similar time. Mary appears to be wearing the same pendant in both, most likely one given to her by her fiancé Philip.
The reverse of the medal depicts the figure of Peace, holding olive branches and setting fire to arms and armour - a somewhat ironic image for 'Bloody Mary', as she is better remebered for burning people.
It sold for £276,000 ($455,300 in today's prices), breaking the world record price for a medal (£243,000) which it had set itself in 2005.
Just discovered the joys of Renaissance medals? Take a look at the Michael Hall collection too.
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