In 1994 I attended a symposium at University College London to celebrate the centenary of William Ramsay's discovery of argon. In a rather remarkable presentation there some slides were shown of some beautiful clear large crystals in a sealed quartz flask. If my memory is not playing tricks on me, I think the lecturer said something even more surprising: that the crystals were the result of leaving an equimolar mixture of xenon and oxygen in the flask to be irradiated in strong sunlight in the middle of a sports field. After the photographs were taken the flask was destroyed by throwing stones at it, because the product, an oxide of xenon, was too unstable and explosive to be safely handled in the flask. It is a long shot, but has anyone else a lead on this experiment? A publication? A similar lecture? Some detail that I might have got wrong? I have failed to find anything like it, but would rather like to have a reference.