Loos asserts that, with regards to cladding, no material should appropriate the forms of another:  ‘Art has nothing to do with forgery, with falsehood.’  Even if you (as I) do not believe in a ‘divine soul’, the following passage rings true.

‘But no, you are wrong, all you imitation-and-substitute architects. The soul is too high, too sublime to be taken in by your devices and petty ploys. True, you have our bodies in your power. They have only five senses to rely on to distinguish genuine from false. And where human senses fail, this is where your domain begins. Paint your best inlays, high up on the ceiling and our poor eyes will accept them for what they appear to be. But the divine soul does not believe your fraud. Even in the best of your ‘looks-just-like-any-inlay’ stencils all it will feel is paint.’

(Also, this has to be one of my favourite architectural insults:

‘Come along, come along, all you champions of imitation, you creators of stencilled inlays, house-ugliful windows and paper-mâché tankards, a new field awaits your talents in Vienna, the ground has been freshly manured.’)