At official exhibitions, such as the Royal Academy summer exhibition, artists, in the past, would give a finishing touch to their works by varnishing them (J M W Turner was known for making significant changes to works on varnishing day while his fellow academicians were simply varnishing). The custom of patrons and the élite of visiting the academies during the varnishing day prior to the formal opening of the exhibition gave rise to the tradition of celebrating the completion of an art work or a series of art works with friends and sponsors. Nowadays, for commercial shows it is an opportunity to market the works on sale to buyers and critics.
There also is a comparable ceremonial ending of art exhibitions, called finissage. Larger art exhibitions also may have such an event at half time of the exhibition (midissage).