The fundamental principle in freeze drying is sublimation, the shift from a solid directly into a gas. Sublimation occurs by lowering the atmospheric pressure and controlling the temperature so that the solid (ice) begins to thaw but not turn to liquid. Instead, the solid (ice) turns to gas, which is removed safely from whatever is being freeze dried. This concept was put to use effectively during World War II by the U.S. Government to collect and store human blood plasma. Later, the food and drug industries used freeze drying. They saw the huge benefits of its preservation qualities. The process has since gained widespread popularity among certain industry segments as a means to recover and preserve valuable documents damaged by water.
First, the item(s) being restored must be frozen solid. This maintains the integrity, shape and form of the item(s). In this frozen state, the item(s) can be stored indefinitely without risk of additional damage. Other drying methods, like vacuum drying, simply do not afford this significant benefit. Drying using vacuum alone takes more time and allows liquid to remain until evaporation occurs. Inks and dyes can still run, stick and stain. Distortion or expansion can occur on printed pages or other materials. Decay or mold can also occur if liquid still exists.