Bull polishing

Bull polishing, bulling, spit polishing or spit shining refers to a method for polishing leather products in such a way as to give an extremely high shine effect. It is commonly used in the military as a traditional method of presenting leather accessories (such as a Sam Browne belt) and boots for inspection. The finished effect should leave the surface of the leather highly reflective.

Ultimately, the process involves polishing the applied thin layers of polish, not the leather itself. The process can be lengthy and is best learned with practice. The down side to this method is that the slightest touch to the laminated layers of brittle dry polish could end up with them cracking or even shattering like glass or even the leather breaking up as the nourishment supplied by the oils in the polish never actually reached the leather.

There is great debate as to the best method for bull polishing, to a point where a lore may be said to exist. Among techniques advocated are melting the polish, the addition of cigar ash to the polish, and substituting coffee for water or spit. However, the basic principles remain the same:

...
Wikipedia