This vintage cobalt blue glass eyewash cup is a unique and collectible item marked with a diamond, and a W, or M inside. Its apothecary design adds to its charm and appeal to collectors of optical items. The vibrant blue color and distinct markings make it a standout piece for those interested in science and medicine history. This eyewash cup is sure to be a conversation starter and a valuable addition to any collection of vintage medical equipment or optical collectibles.