The cylinder could have been sealed airtight. Each bulkhead could be sealed by watertight doors. These he placed in a box which he sealed and left with the prisoners. When they are completely sealed in rubber they are water resistant. Sometimes the powder is sealed with vacuum in a glass ampoule. A single mausoleum may be permanently sealed. Finally, the surface was sealed with a transparent varnish. They are not permanently sealed, but are designated to be maintenance free. Walls of reality closed, the worlds were sealed. They were then sealed at the ends with wax. The seams of the sarcophagus, however, were not properly sealed. The coffin may be sealed with nails. The bag is then sealed with a band or string. After drying the ampoules were sealed under nitrogen. Some designs avoid sliding surfaces altogether by using diaphragms for sealed pistons.