Following the Napoleonic invasion of the Rhineland and the ensuing secularisation of the monasteries, the church became the property of the town of Boppard. The windows were sold to Count (later Prince) Hermann von Pϋckler, a German nobleman, after he had agreed to pay an insignificant purchase price and to replace the coloured glass with blank glazing. As far as we know the Count acquired all seven windows which he intended to install in the chapel on his estate at Muskau, on the Polish border. Eventually one half-window was installed (albeit after his death), while the others remained packed in cases. Upon his death in 1871, his heir, Count Pϋckler-Branitz, sent the remaining 6 ½ windows to Berlin for restoration at the Royal Institute for stained glass and subsequently sold them to a French art collector and dealer, Friedrich Spitzer (who presumably acquired all the glass except the half-window at Muskau).
Spitzer was a French art collector and dealer. He amassed a famous private collection of antiques, Medieval and Renaissance art, arms and armour. Three years after his death in 1890, his collection was publicly auctioned over 3 months raising around 10 million francs. The sale included the Boppard windows, which were dismantled, and sold piecemeal. The catalogue for the sale cost 1,200 francs! Most of the collection was bought by the Australian-born but London-based private collector George Salting (1835-1909), who bequeathed his collection to the British Museum, the National Gallery in London, and the Victoria and Albert Museum.
The surviving windows are now spread across the world, in:
• the Burrell Collection in Glasgow,
• the Metropolitan Museum in New York,
• the Detroit Institute of Arts,
• the Hessisches Landesmuseum in Darmstadt,
• the Schnutgen museum in Cologne,
• the Ochre Court in Newport,
• the Cloisters in New York,
• the Fine Arts Museum in San Francisco.
Several panels that were know to exist are now lost and may have been destroyed or may be in collections around the world waiting to be discovered.
This information was taken from “Learning from Muskau: The Throne of Solomon Window from the Carmelite Church at Boppard and its Donation by Jakob von Sierck, Archbishop of Trier(1439-56)” by Rüdiger Becksmann