The Manners teaspoons by London artist Nicole Wermers were commissioned for public use in the Tate cafe and restaurant but have been disappearing since the opening two weeks ago.
"Regrettably a number of spoons have been taken from Tate Britain since we started using them," Tate told Dezeen. "The vast majority of visitors have enjoyed using the spoon without removing them from the areas in which they are being used."
Wermers made each end of the spoon different to reflect the changing shape of teaspoon bowls at different points in the twentieth century: the smaller end references the 1950s and the larger references the 1980s.
The spoons have been in use alongside otherwise regular cutlery since the reopening of the refurbished Rex Whistler restaurant, and the newly created Djanogly Café and Members Room.
London architecture practice Caruso St John completed the £45 million renovation of the Tate Britain gallery earlier this month.