Thank you, Antwerp, for the great pictures. I too am an enthusiast of 18th century "Belgian" glass. It's great to find myself among fellow collectors.
I've been pondering over the same questions that Antwerp has formulated on this forum. Since a year or so I have been reading most of what can be found on Zoude and Nizet. The literature has not provided me with a definitive answer. Nevertheless it provides clues and I am optimistic that we will find the final answer in the future. We will be able to rely on modern chemical analyses and some attributed examples and perhaps archaeological finds in public Belgian collections.
So what do we know? Most of the information that follows is based on the following two works.
- La Verrerie Zoude et les Cristalleries Namuroises. Alain Douxchamps, 1979.
- Het Glas in België. Luc Engen, 1989.
Zoude opened his glasshouse in 1754 and immediately disposed of an important quantity of minium (lead oxide). It seems he was adding small quantities of lead to his glass, but hadn't really discovered the secret of English crystal until 1762, when he wrote to the States of Namur that the secret had been revealed to him by a labourer at a newly established English glasshouse in Middelburg, Zeeland. His purchases of minium indeed show a stepwise increase around this time. Zoude reported that four of his glasses weighed as much as six from Liège (presumably Nizet). By 1768, Zoude had to be moved to a mental hospital. He was almost certainly suffering from lead poisoning... His wife Marguerite Pétiaux took over the lead with the help of one of her sons. In 1776, they decided to gradually abandon the production of English crystal, because it was found too expensive. In 1779, Zoude died and one year later his widow reportedly tried to sell the minium stock they were no longer using.
It is clear that Zoude copied the design of glasses from the Nizet glasshouse, which had been operational in Liège since around 1710, as he copied from others. Both Zoude and Nizet produced rib and nut moulded glasses and Nizet did so long before Zoude. In fact rib and nut moulding were already applied in the Façon de Venise, see http://www.auctions-fischer.de/kataloge/online-kataloge/232-europaeisches-glas-studioglas.html?kategorie=4&artikel=47625&L=&cHash=2bdf0565cd
for example. Unfortunately we can't tell from the presence of lead alone whether a glass is Nizet or Zoude. On the one hand Zoude did not only produce lead glass, but also "ordinary crystal" without lead. On the other hand it is known that the Nizet glasshouse disposed of a recipe book from 1705 in which several glass compositions are given with minium or cerrusite (lead carbonate). So it is very probable that the Nizets experimented with lead in their glass. Most likely, though, this would have happened in the earlier days, before Zoude came into play.
We can't rely too much on the Zoude Catalog, as there are serious questions about its origin, see http://www.cmog.org/library/assessing-authenticity-putative-sebastien-zoude-catalog-1762
As a guideline I would say that if you have a somewhat primitive or stylistically early and zero or low lead glass, such as http://www.scottishantiquesinc.co.uk/georgian-wine-glasses/18th-century-continental-glass?product_id=1027#.VRsJH_msXHQ
, Nizet is the most likely producer. If you have a later looking and higher lead glass, Zoude is more likely, see http://www.scottishantiquesinc.co.uk/zoude-namur?filter_name=Zoude#.VRsK9fmsXHQ
. From my collecting I also get the impression that Zoude mostly produced glasses with folded feet, where Nizet seems to have produced also a lot of glasses with plain feet.
I'll be happy to participate in any further discussions.