London diamond dealer Laurence Graff is putting 30 works of art on the auction block, including some important contemporary pieces. Collector and philanthropist Louise Blouin MacBain just auctioned off $4.6 million worth of Hermès handbags, Manolo Blahnik shoes and furniture from two of her homes. And an anonymous European seller is parting with 29 pieces, including works by Andy Warhol, Edward Ruscha and furniture designer Marc Newson.

These sales -- and a host of other prominent works headed for the auction block in London in a few weeks -- are sending a ripple through the art market. With an unusual number of works up for sale, some dealers and collectors say they are concerned about signs of potential weakness in what has been a gravity-defying market for years now. Some dealers are referring to the series of London auctions that kicks off Oct. 12 as "Judgment Week" -- a potentially watershed moment. Market players will be watching the level of bidding for signs that a downturn is at hand.

The sheer volume of works planned for sale is fueling the nervous buzz. Christie's has estimated the works it will have on the block at its major London sales in October at $154 million -- compared with the $83 million it made at those sales last year and $33 million in 2005. Sotheby's is selling 387 works at its London auctions next month, compared with 254 last year and 206 the year before.

The London sales come at a time when the art market's anxiety level about a bursting bubble is reaching new heights. Turbulence in the financial markets has some collectors and dealers worried about Wall Street's woes spilling into the art world.