I believe platinum is the most heavy metal, then comes gold, then comes silver. The metal palladium (a sort platinum) however is lighter than silver. So in theory a platinum or golden frame replaced by a palladium frame can result in half the original weight.
I am not sure about it, but it looks like the diadem worn by Queen Máxima on Investiture Day has been re-set. When it was re-set in a metal like palladium, that would have made it much lighter. Even so light that Queen Máxima could wear it without a wrapping around the frame.