This primary market artwork is a Trial Proof; it refers to a proof impression printed during the development of the matrix (any printing surface, such as a metal plate or a lithographic stone) to demonstrate the outcome of specific revisions or corrections, or to test the effects of a particular ink color or inking technique. If retained, they are generally inscribed (as opposed to being numbered), making them completely unique. They are hardly ever authenticated by the artist and are only signed if he or she feels like they are a unique and desirable variation.