Jonathan Archer using a paint brush
A paint brush used for "cosmetic transformation"
An ink brush
A paint brush or ink brush was a tool used to bring up paint on a model or painting.
In 2121, a young Jonathan Archer used a paint brush to color his remote controlled model spaceship. (ENT: "Broken Bow")
In 2151, Doctor Phlox used a paint brush to made final adjustments on Hoshi Sato's Akaali look after he prepared her for this undercover mission. (ENT: "Civilization")
In 2266, a crewman afflicted with polywater intoxication used a paint brush to paint words on the walls of USS Enterprise. (TOS: "The Naked Time")
Keiko O'Brien's grandmother, whom she called obachan, used an ink brush when creating pictures of Japanese calligraphy. (TNG: "Violations")
Captain Jean-Luc Picard also used a paint brush while painting. (TNG: "A Matter of Perspective")