Nichiban #251 Artist Tape is a cut above other artist tapes.

Even on the most delicate surfaces, it will provide a crisp and damage-free seal. It's perfect for creating borders or masking out areas within a painting. Paint won't seep under the edge, and you won't see any pooling of pigment on top of the tape when you paint over it.
 
Made in Japan by shop-favorite Nichiban, each roll measures 18m (59') long, and we carry three width options:

Narrow - 9mm, about a quarter inch
Medium - 12mm, about a half inch
Wide - 24mm, about one inch