An extender, also known as a filler,[1] in printing ink technology is a white transparent, or semi-transparent, component whose purpose is to reduce the cost of the ink, by increasing the area covered by a given weight of pigment.
Extenders are typically white inorganic solids.
[2] Their transparency in inks is frequently due to their refractive indices being similar to the ink,[2] as opposed to opaque pigments, which are generally substantially higher.
[1] Extenders primarily serve to reduce the cost of the ink, but can also impart useful properties to it.
[2] Extenders can also be used to adjust the ink's consistency and viscosity.