As Friday's deadline looms for entries in this year's Archibald Prize, portraits are piling up in their hundreds on the packing room floor at the Art Gallery of NSW.

A very serious Brendan Nelson on canvas glares at Kerry O'Brien's likeness across the room. Works from Archibald veterans, including Rodney Pople and Paul Jackson, share floor space with the paintings of unknown amateurs.

The most unusual entry so far comes from Tim Patch, who calls himself Pricasso, after his pants-down, no-brushes-required painting method.

To create his nude self-portrait, Patch dipped his penis in paint and applied it to the canvas. He first entered the prize last year with a painting of the plastic surgeon Dr Joseph Georghy, but failed to impress the judges with his technique.

"It's not like a running race where there's a clear winner," Patch said at the gallery yesterday after delivering his work. "It's just people's perception of what's good and what's not. I can usually get a pretty good likeness, but I guess I am breaking the boundaries a bit."

Patch spruiks his wares at Sexpo festivals around the world, creating 20-minute masterpieces on paper. He discovered his talent two years ago at a New Year's Eve party, and with this year's Archibald entry, learnt to suffer for his art.

"Painting on canvas for hours on end is not very kind to your skin. It's pretty tiring and it gets really sore … I use antiseptic, but I had to use my bum to paint in the background, because you have to have the occasional break," he said.

As many as 700 paintings are expected to arrive at the gallery before 4pm on Friday, giving the board of trustees less than week to select the finalists for next Thursday's announcement.