De-icing is the process of removing frozen contaminant, snow, ice, slush, from a surface.
Anti-icing is the process of protecting against the formation of frozen contaminant, snow, ice, slush on a surface.
Deicing can be accomplished by mechanical methods (scraping, pushing); through the application of heat; by use of chemicals, known as deicing fluids, designed to lower the freezing point of water (various salts, alcohols, glycols); or by a combination of these different techniques. Deicing fluids are always applied heated and diluted.
Anti-icing is accomplished by applying a protective layer, using a viscous fluid called anti-ice fluid, over a surface to absorb the contaminate.
All anti-ice fluids offer only limited protection, dependent upon frozen contaminant type and precipitation rate. A fluid has failed when it no longer can absorb the contaminant and it essentially becomes a contaminant itself. If it fails it must be washed from the surface using a deicing fluid.
This is a picture of the nose of the airplane. As you can see, there are frozen rivulets down the surface of the airplane. The FBO had a very small, low powered deicing spray system, which just melted the snow. By the time they got around the whole airplane, the water had refrozen. Since it was snowing so hard, they could have lapped the airplane many times trying to remove this fluid, because they had no anti-icing fluid. So we just canceled the trip and went in the morning. Tomorrow I will show more pictures of the deicing process.