From colourful mermaid hair to pastel locks and granny 'dos, there's no shortage of unusual ways to give lacklustre tresses a whole new look.

Now there's a new colour technique on the block - 'oil slick hair', which was developed by New York-based colourist Aura Friedman to jazz up darker hair without bleach.

Using intense purple, blue and green tones on an inky base colour, the process results in an iridescent effect also known as 'duck feather'.

The oil slick hair process creates an iridescent effect. Pictured, the look created on a Seattle model

Speaking to Popsugar, Ms Friedman said: ‘I’ve been trying to recreate gasoline or oil when it’s on the ground and it rains.

'I find that when you take a dark purple and a dark green and layer them one on top of the other, you end up with this iridescent feeling.’

According to Ms Friedman, the technique requires much smaller amounts of bleach, with the result that locks are left in much better condition.

Unlike whole-head trends and lighter pastel shades, the deeper colours used to create the oil slick effect don't fade so quickly.

Less bleach is required so locks are left in much better condition. Pictured, an example shared by London's Blue Mango Salon, which took 4.5 hours

Unlike with pastel shades, the deeper colours used to create the oil slick effect don't fade so quickly. Pictured, an example created by Michelle Phelps at Picasso hair design

Miss Friedman, who works at the world-famous Sally Hershberger Salon, boasts more than 28,000 followers on Instagram and is famed for her complex colour techniques.

In fact, the Israel-born hair expert is largely credited for sparking the hugely popular ombre trend after bleaching the ends of singer MIA's locks in a style she dubbed 'surfer hair'.

She then popularised the 'splashlights' effect - a streak of highlights that move horizontally across the hair and was used to dress up Chairlift singer Caroline Polachek's tresses.

The trend is being praised for its ability to add colourful dimension to darker hair

The effect varies in its intensity, and is also known as 'petrol' or 'duck feather' hair

Since then, Ms Friedman has worked with Jennifer Lawrence, Sophie Dahl, Lady Gaga and Santigold, as well as numerous models.

Her trademark trick, she says, is creating bold hair colour statements without making her clients' tresses look too unnatural.

In another interview, she told HelloGiggles.com that she '[keeps] the look organic by emulating nature, keeping the roots darker, ends lighter. . . no matter what colour or shade.