When Scott Wade's car gets covered in dirt, he doesn't just write 'clean me' in the grime - he uses it to create an intricate masterpiece.

In fact, dirty cars are the perfect canvas for his unusual art and he has built up an impressive collection of pictures of 'grime art' from Leonardo Da Vinci's Mona Lisa to a portrait of Albert Einstein.

The images are so incredible that motorists often stop at traffic lights and jump out of their own cars to admire them.

He creates the pictures, which have also included a life-like face of footballer Ronaldinho, on the back windows of his and his wife's cars using his fingers and an assortment of brushes.

'Almost everywhere we go, my wife and I get people gathering around our cars to take pictures and ask questions,' he said.

'My wife once stopped at a red light and the people in the car behind her jumped out to take pictures with their camera phones.

'A guy even blocked me in as I was leaving a car park - he apologised, but asked me to stay there while his daughter went back to the shop to buy a disposable camera.'

Mr Wade can spend up to four hours perfecting his dirt drawings but admitted one heavy downpour could destroy his hard work.

He said: 'It's surprising to some that the wind and turbulence caused by driving down the road really doesn't affect the drawings much. But a good downpour does.

'Sometimes I feel a little twang of regret when the drawing is washed away, but it's also really great, because that means I get to do another one.

'If it doesn't rain the drawings can last for a month or so but they will slowly degrade during that time.

'The impermanence of this art form is one of the things I really love about it. For one thing, it helps me to not take it too seriously and to really have fun with it.'

Mr Wade doesn't always wait for his cars to get dirty enough to draw on. In most cases he has to apply the dirt himself.

He rubs oil onto the window and buys bags of Fuller's earth, the type used on film sets, and uses a hair dryer to blow the dirt on.

The process takes ten minutes, much quicker than the seven days Mr Wade said it would take to build up a 'natural' canvas by driving a car up and down a dirt track.

He said: 'Although I really love a "natural canvas" sometimes it just isn't practical to find a dirt road and drive around for days collecting dust.

'It takes about a week and a half to build up a proper canvas - if you try to do it in a single day, the dirt just falls off the window.'

Mr Wade, a graphic designer from Wimberley, Texas in the US, explained his dirty car art began as simple doodles in the dust on the rear windows of cars.

He said: 'I lived on a long, dirt road for over 20 years. Our cars were always dirty and I would often doodle in the dust on the rear windows of our cars.

'Mostly I would draw funny faces, then I started experimenting with ways to get shading.

'At first I would use the pads of my fingers and brush very lightly to get grey tones.

'Once I tried using the chewed-up end of a popsicle stick as a brush - I liked the effect, so I started trying paintbrushes, and eventually developed the techniques I use today.'