Colloidal silica is a liquid dispersion of very small, spherical particles of pure silica. The particles used in the finishing aid are about 5 nm (less than 2 ten millionths of an inch)—so small it is difficult to image them even with an electron microscope. (The particles seen here are under electron microscopy are much larger at about 115 nm.) This gives them a vast surface area proportional to their weight, and makes them highly reactive.
