The Chartpak Spectra AD Markers are an alcohol-based twin tip marker featuring brilliant color with less odor than the traditional AD Marker. Painstakingly developed over several years, Spectra AD Markers were designed tip to tip, inside and out, with the artist in mind. Each air-tight cap closely matches the marker's ink, the barrel is ergonomically shaped and prevents rolling, ink capicity allows for maximum draw out, and the twin nibs offer the artist a wide range of line options in one marker.