Pieter Post worked at the leading edge of Dutch classicism, and the house he built for Willem Willemszn Dedel reads like a confident essay in proportion. The exterior is sober brick and stone. The interior, though, was where the Dedels showed off. The rococo staircase of 1735 climbs under a stucco cupola attributed to the Italian Joseph Bollina, who choreographed plaster and daylight as if they were dancers. Seven ceiling paintings by Jacob de Wit float overhead - Hercules received into Olympus, allegories of inheritance - flanked by fourteen of his grisailles and at least five upper-door pieces. There were tapestries from Brussels, gilt leather wall coverings, chandeliers with scenes from Ovid's Metamorphoses, and walls hung with imitation Japanese gold leather wallpaper the Dutch called kinkarakawakami. It was a house built to be looked at, in light managed for the looking.

Houses like this rarely keep their gifts. Shortly after 1871, the noble Melort family - who had inherited the property - sold the entire interior to the Viennese branch of the Rothschilds for 25,200 guilders, with The Hague antiques dealer Leon Sarluis probably acting as the middleman. The ceiling paintings, the grisailles, the chandeliers, the tapestries - everything that made the house a small palace - was packed off to Austria. Then came 1938 and the Anschluss. The Rothschilds were Jewish, and the Nazis seized the collection along with most of what the family owned in Vienna. The plundered interior was earmarked for the Fuhrermuseum that Hitler intended to build in Linz, a museum that, mercifully, was never realized. The objects spent the war hidden in the salt mines at Altaussee, where so much looted European art waited out the bombing in cold, dry darkness.

After the war, Allied recovery teams pulled the Altaussee hoard back into daylight. Most of the Dedel House interior was restituted to the Rothschilds and then scattered: a doubled-in-size Jacob de Wit ceiling now hangs in Waddesdon Manor in Buckinghamshire, and chandeliers from the house light the Neue Burg wing of the Hofburg in Vienna. The Dedel House Foundation, working with the Rothschild family, has been quietly stitching the room back together where possible - some tapestries have already returned. The building itself reopened to the public in 2022 after a long restoration backed by the Province of South Holland, its exterior finished in 2020. It is a Dutch national monument of the highest grade, and inside, the original 19th-century wallpaper still climbs many of the walls.

Design Museum Dedel does something unusual: it does not own its art. The museum was opened on 1 July 2019 by Hedy d'Ancona with an exhibition celebrating two graphic designers who were both 90 years old that year - Milton Glaser, who drew the heart that made New York a verb, and Wim Crouwel, the Dutch typographer whose grids shaped a generation. The COVID-19 pandemic shuttered the project before it had really started, and the museum effectively reopened in 2022. It runs on private money and volunteer staff. Exhibitions are built from loans - more than 70,000 posters from the ReclameArsenaal collection covering 1880 to 1980, and over 40,000 wallpaper samples from 1880 to 2000. Because the Dedel House itself preserves so much historical wallpaper, the museum has begun collecting it as a discipline of its own, archived separately and accessible through the International Institute of Social History in Amsterdam.

Posters and wallpaper are odd things to take seriously. Both were made to be peeled away, glued over, replaced when fashion turned. The museum's argument is that exactly because they were disposable, they carry the unguarded record of how ordinary people wanted their rooms and their streets to feel. The same building that once held Jacob de Wit's gods now holds a century of advertising for cigarettes and KLM and Dutch chocolate. The two centuries do not feel in conflict. They feel like the same conversation about surfaces, taste, and the strange persistence of decoration - argued out, on the canal side of The Hague, in a room where light still finds Magdalena Dedel on the anniversary of her death.