The architect I.M. Pei asked me to make a sculpture for his new extension to the National Gallery in Washington. When we had to decide, he came to my studio with photographs, plans and scale drawings of the building and suggestions of where he thought a sculpture could be placed. This was at the entrance to the new building. We both agreed that whatever sculpture it was, it would have to be on a very big scale, otherwise it would look like somebody going in and out of the gallery. After some consideration we both thought that an existing sculpture, the Knife-Edge Two Piece, would be the right idea if made big enough, but we both agreed that if it were the other way round, that is, a mirror image of itself, it would suit better the entrance because people could go through it into the gallery, whereas the other way they would be running into the wall. I thought it was a good experiment for me to have to do a sculpture as a mirror image. This was done and I think successfully.... Henry Moore in a 1980 audio recording with David Mitchinson, HMF Archive