  Diagrammatic techniques are invented to implement QCD gauge transformations.
These techniques can be used to discover how gauge-dependent terms are
cancelled among diagrams to yield gauge-invariant results in the sum. In this
way a multiloop pinching technique can be developed to change ordinary vertices
into background-gauge vertices. The techniques can also be used to design new
gauges to simplify calculations by reducing the number of gauge-dependent terms
present in the intermediate steps. Two examples are discussed to illustrate
this aspect of the applications.
