Product Description Almost 20 years ago, Princeton gave artists a synthetic version of sable that was almost the equal of fine Kolinsky and is still the standard for performance for its rivals. Neptune is Princeton’s synthetic version of squirrel hair, which they believe may actually outperform the natural version. Neptune is their ‘thirstiest’ brush ever. Neptune is offered in range of shapes including mottlers and quills. The beautiful sea glass handles of Neptune’s aquarelle brushes inspired the name of the line.