It comes under a number of names; naive art, outsider art, art brut, raw art, primitive. For a better description, collector Mark Schaller prefers the word "uninformed", a reference to the artists' disregard for the conventional way of doing things.

This is not meant as a criticism. Schaller, himself a trained artist, finds inspiration in those who aren't conventional. Pablo Picasso was another who felt this way, famously saying that it took him a lifetime to learn how to paint like a child.

There are those who have a natural ability to see with the eyes of a child and, whatever you want to call it, such work is now collectable and steadily gaining in value.

Take the late Selby Warren, whose untrained eye resulted in some works of genius. When he was alive (he died in 1979 at the age of 90-plus), Warren's work was available from his tin shed gallery at the Abercrombie Caves in New South Wales. Those who picked up one on their travels would be pleasantly surprised to see how much these paintings are now worth.

One piece, Untitled Figure (After Davida Allen), appeared in a 2008 Menzies Art Brands auction where this example of naive art sat comfortably alongside work by established contemporary artists like Adam Cullen and Reg Mombassa. The Selby Warren sold for $1300, a few hundred more than Mombassa's Smoking Monkey, $600 less than Cullen's Grape Ape.

Warren has already had a retrospective exhibition, Without Borders, at Monash University in April 2008. And there are other indications of growing awareness of this sub-culture. The Australian naive phenomenon, and related movements like outsider art, was given coverage in a recent edition of Artlink magazine (Vol 12, No. 4). There are too many names to list here but the likes of Sam Byrne, Lorna Chick, Gwen Clarke, Harold 'Kangaroo' Thornton, James Fardoulys, Bernard Jeffery, Bill Yaxley and Ivy Robson are already starting to appear in mainstream auctions. And they are selling.

Sydney gallery owner Ray Hughes has a collection of naive art, including some fine examples of the extraordinary work of Fardoulys, a taxi driver who only began to paint after retirement. And there's also interest from unexpected quarters.

"That style of art has a great deal of corporate appeal," says Ralph Hobbs, a director of Art Equity, the art investment company that also rents out original artwork to the corporate sector. Indigenous art is the "most rented" category but naive work is also popular, as is the work of contemporary artists influenced by that genre.

Art Equity has recently exhibited the paintings of Schaller, who has also had great success in the corporate rental market.

"It works for the same reasons," says Hobbs. "It has broad appeal and raw energy."

Schaller was one of a group of young Melbourne art school graduates who founded the famous Roar Studios collective in Brunswick Street, Fitzroy, in 1982. The most prominent of the Roar artists is David Larwill, who has "gone stratospheric", according to Hobbs. Top price for a Larwill at auction is $216,000 earlier this year.

Schaller's work now sells for up to $25,000. Other Roar artists include Sarah Faulkner, Jill Noble and Mark Howson. These are not naive artists by definition but they painted in an untrained way as a protest against the restrictive art industry.

"The essence of primitivism," says Hobbs.

This tradition continues. One to watch, according to Hobbs, is George Raftopoulos, a trained artist from the western suburbs of Sydney who paints in an abstract primitive style. He's already held a solo exhibition, at the Tim Olsen Gallery in 2008.

This style of art is now popular around the world and includes such unexpected influences as the German expressionist Lovis Corinth who suffered a stroke in 1911 and was forced to learn to paint again using his (non-preferred) right hand. Because of this handicap, his work after the stroke is less traditional and is now regarded as much more valuable, especially the landscapes leading up to his death in 1925.

My collection

Melbourne artist Mark Schaller was a founding member of the Roar Studios collective, which began in Brunswick Street, Fitzroy, in 1982.

'We were all disenchanted with the current system," he says. "But we all had a love of naive." He still loves this style, and works by Australian naive painters Sam Byrne, Jim Fardoulys and Selby Warren hang on his walls.

Perhaps his proudest possession is a drypoint etching by celebrated German expressionist Lovis Corinth, who was forced to paint with his non-preferred hand after a stroke. He found this work at Camberwell Markets 10 years ago. It had a price tag of $25.

The mount covered the signature so he wasn't certain it was a Corinth until he got it home. He later identified this work as Bank Im Walde II, then got in touch with Sotheby's in London, who told him it was worth about ?2000. An identical etching, in average condition, sold earlier this year for $1500.

$250

This study of a sulphur-crested cockatoo by an unknown artist is a treasured part of the Mark Schaller collection of naive art. He got it in a swap but thinks it could fetch up to $500 at auction.

$1000

The extraordinary art of James Fardoulys, retired taxi driver, is now starting to fetch good money on the secondary market. This work is Dolly On A Picnic.

$2000

This dramatic painting of bushrangers by naive artist Selby Warren has interesting parallels with Sidney Nolan's iconic Ned Kelly series. Warren's work is increasingly being seen as significant.