Yes, we were amazed when that happened. It was a real joke to us. Konrad Lueg and I did a Happening, and we used the phrase just for the Happening, to have a catchy name for it; and then it immediately got taken up and brought into use. There's no defence against that - and really it's no bad thing.

The first colour charts were unsystematic. They were based directly on commercial colour samples. They were still related to Pop Art. In the canvases that followed, the colours were chosen arbitrarily and drawn by chance. Then, 180 tones were mixed according to a given system and drawn by chance to make four variations of 180 tones. But after that the number 180 seemed too arbitrary to me, so I developed a system based on a number of rigorously defined tones and proportions.

The painter sees the semblance of things and repeats it. That is, without fabricating the things himself, he fabricates their semblance; and, if that no longer recalls any object, this artificially produced semblance functions only because it is scrutinized for likeness to a familiar - that is, object-related - semblance.

I first came up with the idea for the colour-chart pictures back in 1966, and my preoccupation with the topic culminated in 1974 with a painting that consisted of 4,096 colour fields. Initially I was attracted by the typical Pop Art aestheticism of using standard colour-sample cards; I preferred the unartistic, tasteful and secular illustration of the different tones to the paintings of Albers, Bill, Calderara, Lohse, etc.

Perhaps the Doors, Curtains, Surface Pictures, Panes of Glass, etc. are metaphors of despair, prompted by the dilemma that our sense of sight causes us to apprehend things, but at the same time restricts and partly precludes our apprehension of reality.

Almost every work of art is an analogy. When I make a representation of something, this too is an analogy to what exists; I make an effort to get a grip on the thing by depicting it. I prefer to steer clear of anything aesthetic, so as not to set obstacles in my own way and not to have the problem of people saying: 'Ah, yes, that's how he sees the world, that's his interpretation.'

If the abstract paintings show my reality, then the landscapes and still-lifes show my yearning.