Gabion: Thomas Heatherwick and Newcastle’s Blue Carpet. 1/3

“Well,” says Tom Heatherwick, slightly defensively, “I think it’s blue enough.” This is possibly the oddest defence of a work of art since Turner had to explain why all his paintings were so yellow. But when the work in question has been six years in the making, takes the form of a new public square in Newcastle, and has always been described as a “blue carpet”, well, people expect blue. They expect Yves Klein blue, or its close relation, Will Alsop blue. What they get with Heatherwick’s square is grey with a sparkly hint of blue. Some Tynesiders have been muttering that it’s not blue enough. Hence Heatherwick’s defence.

Such are the pitfalls of public art. The whole point of the new place is the beguiling if fundamentally absurd idea that this hard masonry object is a carpet - curling up a little at one corner, with benches mysteriously peeled in strips out of this pretend-fabric, with bollards pushing though rents in it. Beneath the carpet is, not floorboards, but a mysterious world of hectically-coloured neon light, glimpsed through glass. So it is a magic carpet, then. Moreover, someone has been sweeping something under it. It is not flat, but a very shallow dome. Your knees sense this as you walk across it. It is mildly disconcerting, as is the deliberately overscaled laminated-timber spiral staircase that descends into the space from an upper level.

It is also - let’s get this over with - indeed not very blue at a casual glance. Heatherwick mixed scrap blue glass - from designer sherry bottles - with resin to get his paving slabs. The trouble is that you can’t put too much glass into such material, otherwise it goes crumbly. So a balance has to be struck. Blue enough, as the man said. Blue enough, he hopes, to last 100 years without fading.