Recap: Telltale Art, Yazzy's at www.walliamverdult.com

According to the New York Times, a GIANT, gleaming blue diamond — about eight feet tall by seven feet wide — is parked on four gold-colored prongs outside Christie’s at Rockefeller Center. Just uptown Christie’s archrival, Sotheby’s, has another sight gag, an eye-catching confection of similar dimensions: a shiny, bright-red dangling heart. These playful if expensive sculptures by the artist Jeff Koons could be a metaphor for the glittered frenzy of this fall’s major auctions, which open on Tuesday with a sale of Impressionist and modern art at Christie’s.

But beneath all the bling — the glossy catalogs brimming with lavish illustrations, the extravagant parties to lure rich collectors, the impressive exhibitions of the art and the optimistically high estimates — lurks an ominous question. After three years of speculation about a bust, will this be the moment when the art market finally crumbles? Auction house experts who have spent the last six months mapping out the sales say the business-getting season fell into two distinct chapters: before the subprime mortgage crisis struck in August, and after.

Flush from their record-setting May and June sales in New York and London, Sotheby’s, Christie’s and the boutique house Phillips de Pury assumed that the good times would roll on. Collectors were feeling optimistic too. As prices soared for artists they collected, many decided to cash in, so much so that an unusually large number of paintings, drawings and sculptures are coming to market.

Some of them have never made a public appearance; other works are all too familiar, having been on and off the auction block several times in just a few years.

To land the best works, however, the houses had to compete against one another, offering the sellers bigger and bigger guarantees, promises of undisclosed sums regardless of the outcome of the sale. If a work doesn’t sell, the auction house must still fork out the guarantee and is often stuck with a burnt piece of art.

Before things got rough Sotheby’s and Christie’s had invested heavily in such guarantees — about $1 billion between them. And even before the mortgage crisis hit in August, both abruptly stopped offering guarantees, feeling they had committed enough money to these sales. But they continued to promise sellers a cut of the fees each auction house charges to buyers. (While cutting significantly into the houses’ potential profits, this was far less risky than guaranteeing a specific cash sum.)

After the tumultuous swings in stock prices spurred by the mortgage and equity crisis and on-and-off fears of a recession, this fall’s auctions loom as a critical test of the art market’s strength.

The sellers include such seasoned collectors as the financiers Henry R. Kravis, Donald B. Marron and Mitchell P. Rales, the actor Hugh Grant and the entrepreneur Adam Lindeman. But who will the buyers be?

Fewer Americans, to hear it from the experts. With reduced bonuses and dwindling profits anticipated on Wall Street, the American buyers who have for years driven the surge in art prices may not be the biggest spenders this time. Instead Sotheby’s and Christie’s are banking on newly rich Russians, Asians and Middle Easterners. Having recently started collecting everything from Renoirs to Rauschenbergs, these collectors find New York a particularly attractive place to shop because of the weak dollar.

“We are seeing a broader base of clients than ever before,” said Marc Porter, president of Christie’s in America. “Americans only make up about a third of our active buyers.”

In addition to what experts call “wall power” — splashy works that shout “status” — some of the paintings, drawings and sculptures up for sale are particularly rare. Christie’s auction of Impressionist and modern art on Tuesday night, for example, includes a shimmering 1889 landscape by Signac painted during a stay in Cassis, a fishing village nestled amid yellow-red cliffs on the Côte d’Azur. The work, whose owner has not been identified, carries an estimate of $8 million to $12 million. The following evening Sotheby’s will offer some unusual works on paper by that are fresh to the market.