More than half the estimated €43 billion spent worldwide last year in the fine art and antiques market was accounted for by private transactions – sales through dealers, galleries, shops and fairs. But public auctions, which accounted for more than €20 billion in worldwide sales, provide the best insight into both prices and trends.

Art critics, designers and auctioneers may laud the merits of a particular painter, suggest that antique furniture is “great value” or claim that Georgian silver is a “safe investment” but, ultimately, fine art and antiques are, like all commodities, subject to the laws of supply and demand.

The major international auctions take place in London and New York where hundreds of millions of pounds or dollars can change hands in a single evening. But who is buying?

Auctioneers don’t release the names of buyers or sellers. Some items are bought by public institutions such as major public galleries, museums and universities, but most are bought by, or on behalf of, un-named collectors and investors. These often bid discreetly via an agent or by telephone or the internet.

The upper echelon of the fine art and antiques business is essentially a trade catering to the world’s super-rich whose identities can only be guessed at. Many lots are glimpsed briefly during pre-auction viewing days before disappearing back into the mansions, villas, yachts or Swiss bank vaults of the global elite, to be seen and enjoyed only by the new owners and their privileged circles.

Most of the world’s richest art collectors are relatively unknown to the general public. And that’s the way they like it. But sometimes word does leak out.

In May, Bloomberg reported that the English jeweller Laurence Graff had paid $56.1 million (€42m) at Christie's, New York for a Roy Lichtenstein painting Woman With Flowered Hat. And why did he buy it? He reportedly said: "I've got a big birthday coming up and I bought it for my birthday." He turned 75 a month later.

The Wall Street Journal reported that New York billionaire financier Leon Black was the mystery buyer who paid $119.9 million for Edvard Munch's The Scream at Sotheby's New York in May 2012. It was the world's most expensive work of art ever to sell at auction.

In March this year, the New York Post reported that the Manhattan investor, Steven A Cohen, "has bought himself a gift, Picasso's Le Rêve for $155 million (€116m)". The paper said he had "secretly bought the masterpiece" from Las Vegas casino mogul Steve Wynn, who, while suffering from poor eyesight, had "famously put his elbow through the 1932 painting of Picasso's mistress, creating a six-inch tear". The price is estimated to be the highest ever paid for an artwork by a US collector. It is believed that Wynn had originally agreed to sell the painting to Cohen for $139 million (€104m) in 2006, but accidentally damaged the painting just before the sale. Apparently, the painting has been impeccably restored.

Could there be a property-style bubble developing in this sector of the art market? How much paintings like this will be worth 20, 50 or 100 years from now is anyone’s guess.

Wealthy collectors are no longer confined to the US and Europe where most of the big sales take place. The ranks of the global rich, many of whom collect art and antiques, are swelling and many of the new plutocrats come from Asia, Russia, Brazil and the Middle East. Last year, a painting by French artist Paul Cézanne, The Card Players, owned by the late Greek shipping magnate George Embiricos was reportedly sold privately to the government of Qatar for more than $250 million (€187m). If confirmed, it would be the highest price ever paid for a work of art.

The fiercely wealthy Gulf state is reputedly on an international shopping spree to stock opulent new museums and art galleries being built to encourage tourism.

Irish art economist Dr Clare McAndrew says the number of high net worth individuals worldwide increased by 60 per cent between 2000 and 2011. It’s estimated that there are now around 12 million such individuals worldwide with investable wealth estimated at a staggering $46 trillion. “Many choose art and antiques with an eye to investment and to diversifying their investments,” she says. “They seek to acquire items with real tangible long-term value as a hedge against inflation and to cushion the financial volatility of other assets, particularly stocks and shares.”

Sotheby’s said last month that its summer 2013 auctions had been a “golden season” and that sales had been “transformed” by “global competition” with one in six buyers from Asia, Russia and the Middle East.

Christie's also reported a big increase in new clients – up 10 per cent on last year – and already this year has sold 422 works at auction for over $1 million (compared to 399 in the same period in 2012) and 34 for over $10 million (30 in the same period in 2012). Overall, Christie's said business for the first half of 2013 was up 9 per cent on last year.

Next week: The Irish art and antiques market