London's National Gallery explores sources and varieties of colour in the history of painting

In 2008 British artist Roger Hiorns flooded an abandoned basement flat in South London with a solution made of copper sulphate. There was so much of it that it came in two shipping containers. A month later, when he drained it, every inch was covered in blue copper sulphate crystals, some of them the size of a human palm.

"You had to put wellies on to go in," recalls Caroline Campbell, the National Gallery of London's curator of pre-1500 Italian paintings. "It was in this disused council flat on Harper Road in southeast London; and from those grim surroundings you stepped into this immersive blue world," she says. "It was one of the most moving experiences I've had."

This - and a lifetime of working with mediaeval and Renaissance paintings and a fascination with materials the artists worked with - was one of the inspirations that led Campbell to work with her colleague, director of collections and colour paint expert Ashok Roy. They have co-curated one of the gallery's most unusual and fascinatingly educational shows of recent years: "Making Colour".

The exhibition, which runs until September 7 and took three years to plan, explores the very materials from which visual art is made.

Each room is dedicated to a colour, starting with blue (including a sample of that mystically immersive Hiorns room) and moving through the colour wheel: green, orange/yellow, red and purple. Missing out black and white ("Which was agonising but we couldn't include everything," Campbell says) it ends with a room dedicated to gold and silver. These colours are famously hard to use in paintings: silver because it tarnishes so quickly to black, and gold because often it does not look nearly as authentic in a painting as a spot of judiciously applied yellow and ochre and gleaming lead white.

The works are mostly from the gallery's own collection but placed together in new colour-organised combinations they tell quite different stories: "For me that's been the biggest surprise," says Roy. "By putting paintings next to each other that have never seen each other before, you learn different things about them."