I know that in the fictional Superman universe, "X-rays" do not work like real X-rays (color, translucence etc.), but for the reader's sake the authors invented the inability to see through lead.
Now is lead not the only substance which is very good to stop X-rays, but all elements with high atomic numbers (many electrons to scatter the radiation). This is hafnium, tantalum, tungsten, all heavy platinum metals, gold, mercury and uranium.
Are these metals ever mentioned to have a similar effect of blocking X-ray vision or are there egregious examples where pieces of the metals above are transparent like glass?
Or are there other fictitious or real materials known to block the vision? In at least one instance I remember people from the far future are sending waste back by time travel and superman encountered a "meteorite" which was so dense that his X-ray vision was useless.