By the late 1930s, the Watt Pottery Company began marking the bottom of the ovenware. The words Oven Ware-Made In USA were marked in the mold on most pieces. Various pieces from this time period bear only the size of the bowl, not the full mark. The authors have not located Oven Ware as a registered trademark, but it appears on nearly all of the pieces of Watt Pottery from the late 1930s until the end of production in 1965. Just be aware that reproduction Watt Pottery pieces have been introduced to the marketplace. You will many times see the Watt Pottery oven ware USA mark on many of your original Watt Pottery pieces.