This, in turn, can require very large and complicated superstructures to distribute the highly concentrated pressure from a high tonnage press ram. Enter the air bladder. Effectively nothing more than a large, flat balloon, an air bladder can be used to distribute equal pressure over a very large area with only a low profile yoke to contain the pressure. The real beauty of the air bladder is that a relatively small amount of pressure delivered by a normal air compressor—say 100 pounds per square inch (psi)—will be distributed at that same 100 psi over every square inch of the surface of the air bladder. A four by eight foot air bladder could deliver 230 tons of pressure simply by being hooked up to a regular air compressor delivering only 100 psi. For the NARA project we needed a forty by forty inch press. Calculations showed that our 100 psi air line would generate a respectable eighty tons of pressure. Ferguson Equipment Corporation in South Bend, Indiana, supplied the required bladder, rated at 100 psi uncontained, at a cost of $1400. For help with the engineering, I called Howie Clark at Twinrocker. He was pleased to hear we were planning to build a pneumatic press for this application. He graciously took the time to calculate exactly what was required to make the press yokes structurally sound. All of the aluminum cross pieces and threaded stainless steel rods were cut by the University of Iowa Physics Machine Shop. Students and I bolted the press together without the need for any welding or special machining. We used a preassembled version of the press to squeeze and glue all of the platen pieces together. Total materials costs were about $5000. Inflated to 100 psi, the exposed part of our air bladder feels like a giant slab of lead covered with a thin layer of rubber. The only real shortcoming of the press is its small (three inch) amount of daylight, or working opening. This limitation is directly related to the height of the uninflated bladder and means that the total size of the lower press board, paper, and felts combined has to be three inches or less. Tim Barrett, with special thanks to Howie Clark