The collection was made up of many objects described by Powell as "antiquities and curiosities" and also included 150 oil paintings, watercolours, prints and drawings (including pencil drawings by Rossetti), 1,700 books, 11 volumes of correspondents' letters, Japanese ivory carvings, a Chinese magician's crystal wand and a fragment of Robert Schumann's coffin.
Holland writes that the collection, although "imbued with Powell's own slant on the world" and "representative of his personal enthusiasms [with] strong significance as precious souvenirs of friends and relics of heroes" included many objects "'without provenance', 'attributed', copies or even fakes." Powell was also "a fanatical devotee" of German composer Richard Wagner and attended the first performance of Wagner's Der Ring des Nibelungen as a complete cycle at Bayreuth, Germany, in August 1876.
An example of a 14th-century mazer, similar in design to the Nanteos Cup.
Who made it is not known, or how it came into the possession of the ancient family of Nanteos – the Powells.
Its healing virtues in certain cases of female disorder were in great repute, and when all hopes from doctors had been given up the sufferer had only to take all nourishment, wet and dry, out of it for a few days to ensure a complete cure.
Their journey was long and dangerous for such old men, but they reached the House of Nant-Eos in safety, and deposited the treasure they had suffered so much to save.
One by one the old monks died, and when the last one was at the point of death he entrusted the treasure to the owner of the house that had sheltered them, until the Church should once more claim its own.
The source of its alleged virtues were supposed to lie in its having formed a portion of the True Cross.