Heavy duty, molded TLC developing tank for use with plates up to 20 x 20 cm (8in x 8in). The weight of the tank is approximately 15 pounds and the bottom is ground to insure stability. The unique latching system holds the matching ground surfaces of the lid and tank firmly in place, enhancing the stability of the saturated atmosphere for the developing TLC plates. All of the metal components of the Latch-Lid mechanism are made of stainless steel.