Phillips, London, 6 June 1991, lot 164 (the first).
Sotheby Parke-Bernet, New York, 30 May 1981, lot 81 (the second cup).
Please note the sulphide portrait in the pale-yellow cup is Friedrich Wilhelm III, King of Prussia. The portrait was originally modeled by Leonhard Posch (1750-1831) in the spring of 1814 in Paris and was used as the prototype for a medal to commemorate the visit of the Prussian King to the Paris Mint. The French medalist Raymond Gayrard created the French medal using Posch's portrait.
Dena Kaminsky, 'Sulphides: "The Noble Simplicity and Quiet Grandeur"', PCA Bulletin, 1984, p. 32, fig. 3 (cup only, the second).
D. Tarshis, Objects of Fantasy: Glass Inclusions of the Nineteenth Century, The Corning Museum of Glass, New York, 2001, p. 132-133, no. 74 (the first).