"We study the materials for a long time. We make maquettes. The main material at this point is stainless steel. We have worked with this material before, but not like this. This is a new idea for us. [With this treatment] the stainless steel has a dappled quality, which captures sunlight and moonlight. We built a whole section of the wall in my office in California. We made it in titanium, aluminium and every other metal and this seems to be closest to the right one. We are 85% there. We need to get a little closer. We have got to build a section here and look at it."