These are vintage pieces fron the iconic Pyrex Primary Colors Nesting Mixing Bowl Set (specfically the 400 series) which was originally introduced by Corning Glass Works in 1945. Proclaimed as the "World's most famous mixing bowl set", this series was the very first colored opal ware (white milk glass with a colored exterior overlay) ever produced by Pyrex The Yellow Bowl #404: This is the largest bowl in the original four-piece set. It has a 4-quart capacity and spans 10.5 inches in diameter. The Green Bowl #403: This is the second-largest bowl in the set. It features a 2.5-quart capacity and measures 8.5 inches in diameter Fascinating HistoryWar Effort Roots: The durable opal glass formula was actually developed as a collaborative effort between Corning Glass Works and the U.S. government during World War II to create heavy-duty, unbreakable dishes for military soldiers. The "No Numbers" Rarity: You can approximate the age of your bowls by flipping them over. If the bottoms feature the Pyrex logo but lack an embossed model number (like 403 or 404), they belong to the earliest first-generation production run between 1945 and 1949, making them highly prized by collectors. (Google)To protect their glossy finish and prevent the paint from turning chalky or scratched, never put vintage Pyrex in the dishwasher. Always hand wash them with non-abrasive sponges. In good vintaged, pre-owned condition. There are some faint stir scratches inside both bowls.