Over the same period, he has put together an exquisite private collection, which should be a high point of the season, when it comes under the hammer at Lempertz in Cologne on July 15.
The 220 lots span the ages, from 2nd century Roman silver to a late 19th century Art Nouveau gold cup Les Vendanges by the Parisian goldsmith Jules-Paul Brateau, decorated with an enamel frieze of a wine harvest by Paul Grandhomme in 1893 (estimated at €120,000-130,000).
Many pieces have a noble, often royal provenance and estimates to match. The top lot is a silver-gilt ewer with matching basin, created in 1770 by the Parisian silversmith Jean-Baptiste-François Chéret for the Marquis and Marquise de Montmelas, which is accompanied by the original design drawings. The catalogue price is €1m-1.2m.
Historically of equal importance is a lapis lazuli hourglass, which Pope Sixtus V presented to Ferdinand I de’ Medici, Grand Duke of Tuscany, on the occasion of his marriage to Christine von Lothringen in 1589. It is guided at €400,000-450,000.
Amber on an altar
Among the costly materials used by craftsmen is amber, which figures prominently in this 16in (41cm) altar from the late 17th century.
The altar incorporates small panels of amber or Baltic gold, as it is sometimes known, in various shades, some of which are mounted in front of gold foil to increase the effect. The front of the base has five niches with carved reliefs of Jesus as the Salvator Mundi, flanked by four saints.
The altar, which once belonged to the abbey in Einsiedeln, near Danzig, is surmounted by an ivory and amber figure of the Madonna with Child.
It is attributed to Christoph Maucher, member of the most accomplished family of amber artists in Danzig around the end of the 17th century.
Lempertz is hoping to achieve €280,000-300,000.