Aside from the unique, economical 21ml tube size, Sennelier Watercolors have other exceptional features. The binder used is a mixture of hand-picked Senegalese gum arabic and alpine honey. The honey gives the colors a rich, saturated appearance and a certain satiny luminosity, especially when applied fairly thickly. The pigments are ground repeatedly on granite grindstones for maximum fineness, allowing flawless washes.