The writing's on the wall for Institute's latest show

In Sculpture in Painting, the only three-dimensional objects on show were represented on canvas.

Now the Institute has gone a step further with its latest exhibition.

"A pencil. 12 walls. 120 hours. 450 square metres.

one exhibition."

This is the sort of cryptic message that has been sent out from the Institute over the past month.

This week, the meaning of the message was revealed, although one doubts the veracity of the claim of "a (singular) pencil".

Scottish artist Alan Johnston must have used many of them to create the current exhibition. He has spent the past three weeks drawing on the walls of the gallery for his latest installation. The piece, on the face of it, is a solid line of scribbles created in geometric shapes. It will be painted over when the exhibition comes to an end on May 2.

As we go into the gallery, where Johnston is leading a tour of the work, he is approached by a fan, who enthuses that the installation piece reminds him of Italian frescoes.

"They were certainly an inspiration," says Johnston.

Seeing nothing on the floors and the white walls bare, save for Johnston's pencil drawings, is a disconcerting experience.

"I agree. I think it will be interesting to see how people react to it," says the artist.

It is easy to wonder, aloud even, to Johnston, if this installation, interesting though it is, belongs in a gallery dedicated to sculpture?

It turns out that far from Johnston creating a piece that has no sculpture, his pencil etching, in fact, turns everything into a sculpture.

His practice, he explains, is about three dimensions.

"The third dimension aspect is the structure itself in which the work exists," says Johnston.

"I refer a lot to ideas of architecture and, in particular, a German idea, Baukunst, which literally means building art. When you look at a building, you are looking at a static, spatial entity that is 98 per cent sculpture. I use drawing to bring out the tactile geometry of the building."

Even though he had three weeks to work on the installation, the labour-intensive nature of covering the gallery walls in pencil proved a huge task and Johnston brought in an assistant to complete the installation.

"It's not something I would normally do, but it is a big space to fill," says Johnston.

"Matt, one of the technicians, was helping and he kept saying, 'What if the lines on the walls don't match up?'

"I explained that was the risk. You can't make a plan for something like this because of the variations with the length and height of the walls and the slope of the floor, so you just have to risk it and trust that it will work."

How does Johnston feel about the fact that some visitors may be non-plussed when they visit the sculpture gallery to find an absence

of sculpture?

"Hopefully, it (the installation) will remind them that architecture is art, building is art, it is sculpture."

Drawing A Shadow: No Object, is at the Henry Moore Institute, The Headrow, Leeds, to May 2. Free entry.