Extenders are mainly natural minerals that are micronised after separating secondary constituents.
From this huge amount of Extenders only a relative small part used in the coating and Ink industry; e.g. 72% of precipitated calcium-carbonate is used in the paper industry and only 8% in paints and 1% in inks. From the natural Aluminium-silicate, Kaolin, 44% are used in porcelain manufacturing and only 3% in paints and coatings (Lückert;6;2002) Synthetic Silica's riches the production figure of more than one million t per year, world wide. Also here, only a relative small amount used in the coating Industry.
According to DIN 55943 extenders are powdered substances, which are practically insoluble in the application medium, used to modify the volume of a system and to achieve or improve technical properties.
Further more, white extenders show pigment similar functions, considering the refractive index is lower than 1.7. Used alone, in a binder, extender produce nearly no hiding power, because the difference to the refractive index of binders, is small. Only with higher Pigment Volume Concentration, in direction to CPVC, the influence of hiding power can be significant.