A new test target for defining the gamut boundary of a printing device is described, which results in a list of vertices on the boundary and the set of triangular faces that connect them. When used in conjunction with an ICC profile for the device in a procedure to compute the gamut volume, this target is shown to give highly-reproducible estimates independently of the CMM. A method of identifying irregularities in the gamut surface is described. Results are shown for a wide range of printers, both for conventional and digital ink-jet systems.