A Dutch journalist investigates the sale of illegally excavated pottery from ancient Greece
NRC’s Theo Toebosch grew suspicious recently when he saw an ancient Greek drinking cup – an intricately decorated piece of pottery known in the trade as a Siana cup (though more like a bowl on a pedestal) – for sale on the website of Dutch antiquities dealer Kunsthandel Mieke Zilverberg.
He’d come across such cups before. Four years ago, in 2021, he wrote another article for NRC about a similar piece of pottery in the permanent collection of Amsterdam University’s Allard Pierson Museum revealed as having been illegally excavated and sold, as indicated by a cache of polaroid photos confiscated in the 1990s from a well-known Italian dealer in illegal antiquities, Giacomo Medici. Could there be a link?
Working with archaeologist Christos Tsirogiannis, Toebosch got to work. Their research led them to the same conclusion for this cup that they had reached for the cup they wrote about in 2021, absent from the sale notes on Zilverberg’s website: “What is not stated: the drinking bowl was once illegally excavated.” This article charts their research journey, a fascinating tour into the underworld of the antiquities trade (or at least how it used to work) – with those rather fantastic polaroids as a bonus.
The article opens with what curators and museologists refer to as the index card of the cup: that is, a document briefly summarising its known history of having been passed from hand to hand or, in the language of the trade, its provenance. In this case: the stated provenance of the Siana cup in question on Zilverberg’s website was that it had come from a Dutch private collection and before that had featured in a summer 1985 auction at Sotheby’s in London.
Scant information but, to Toebosch, suggestive. He describes the giant loophole that was the 1980s art trade: “It was the time when museums and collectors could buy illegally excavated antiquities at reputable international auction houses without any problems. […] Questions about how such a drinking bowl had ended up at the auction house didn’t need any further investigation.” In effect, the prestige of the auction house would launder any questionable goods. As the article makes clear, this could lead to a symbiotic, some might say corrupt, relationship between auction houses and academics.
The next point on the index card was reference literature. In this case, the work of Herman Brijder, who wrote his doctoral thesis on Siana cups and even now, at the age of 80, is still working on a multi-volume catalogue raisonné of all the Siana cups in existence (“About 2,500 in total”, he tells Toebosch over the phone).
Back to Sotheby’s, London, and the summer auction’s preview day in July 1985. The younger Brijder saw two drinking cups he hadn’t encountered before. Sensing an opportunity to secure at least one, Brijder approached the collector H. Pierson, a friend of the director of the Allard Pierson Museum: might he want to buy one, lot 513? (This is the cup that was the subject of Toebosch’s 2021 article for NRC, showing it had been illegally excavated).
The other was rumoured to be a forgery. But Brijder thought that wasn’t right, and when another Dutch collector contacted the academic he was happy to say so. After all, Toebosch notes: “Brijder’s tips and advice might be to the museum’s advantage in the long run if – who knows? – the two collectors ended up donating the vases to the museum”. And so it was that both H. Pierson and J. Van Roozendaal bought one Siana cup each (though Van Roozendaal would only go after the more dubious lot 207 after the auction, buying it “for a relatively small sum due to the rumours”).
Brijder subsequently wrote about both professionally, giving them a further stamp of approval. The Pierson cup featured in the Vriendenblad van het Amsterdamse universiteitsmuseum. In 1991, he catalogued Van Roozendaal’s Siana Cup in the second volume of his catalogue raisonné with the note “provenance unknown” while identifying its painter as someone from Taranto (now in southern Italy, but then known as the Greek colony of Tara) who worked in the workshop of the infamous C-Painter (“the inventor of the Siana cup”, according to Brijder).
The article notes that Brijder’s approach to Siana cups is principally art historical. Vladimir Stissi, his successor as professor at the University of Amsterdam – and a former student – takes an almost antithetical approach to Greek Pottery, chiefly focussed on its production, distribution and reception. “Stissi considers the vases as a utensil from the past”, comments Toebosch, albeit ones associated with a certain luxury. The iconography on the vases often relates to where they were found, and to their probable use: images of battles tend to be found in sanctuaries, for example.
That’s not the only difference. Stissi has spoken out against illegal antiquities; Brijder is more relaxed. Stissi has labelled over 20% of his predecessor’s research as “provenance unknown”, code for illegally excavated objects without any traceable archaeological context. This mirrors internal investigations at the Allard Pierson Museum from 2023 when it became clear that the museum acquired several pieces, including the Pierson cup, during Brijder’s directorship.
Van Rozendaal’s Siana cup, however, was not one of them. His collection was sold after his death in 2009. Eleven years later the Rozendaal cup was consigned to Mieke Zilverberg.
She claims that she contacted Brijder, and he told her “everything was fine” in terms of the cup’s origins. Listing his publication on her website would have given potential buyers reassurance that they were looking at a bona fide Siana cup, unsullied with any hint of illegality. Giacomo Medici’s polaroids, as demonstrated by Christos Tsirogiannis and Toebosch, showed that was not the case. When confronted with this evidence, Zilverberg took down the offer of the cup for sale. What will she do with it now? “Return it to the children of Van Roozendaal”, she told NRC matter of factly.
To Toebosch’s evident dismay, Brijder will continue to list such items as “provenance unknown”, without a reference to the possibility of illegal origins. “Someone has to judge for themselves”, he tells NRC. It’s a classic case of caveat emptor. (The article also quotes his observation: “I’ve myself known of residents of Taranta who bring up Siana cups from their cellars, built on the old necropole”.)
Zilverberg is in favour of adding the “potentially illegally excavated” tag to such items in the future, but notes that the 1985 Sotheby sale made this seem unnecessary. That shouldn’t be the case now Tsirogiannis argues: “The least anyone should do is have an object from that auction checked by the Italian authorities. If they don’t even do that, any further action on their hand is intentional.”
In effect, inaction amounts to complicity, whatever the distance between 1985 and now, let alone between when the cup was made and when it was dug up (and by who).
Original article (“Hoe illegaal opgegraven Grieks aardewerk in de handel kwam bij Mieke Zilverberg”) by Theo Toebosch appeared in Dutch on 13 March 2025 on the NCR website, and in print on 15 March 2025.
It is available here.
NRC is a daily morning newspaper published in Dutch in Amsterdam. It’s widely regarded as a newspaper of record.
Summary by ML.
