Complex sentence: The use of these materials meant that his art works became temporary and fragile, which Kiefer himself is well aware of; he also wanted to showcase the materials in a way in which they were not disguised and could be represented in their natural form.
Split into simpler sentences: The use of these materials meant that his art works became temporary and fragile, which Kiefer himself is well aware of. Also he wanted to showcase the materials in a way in which they were not disguised and could be represented in their natural form.