Water washed kaolin has traditionally been used to produce extenders for use in inks.  Kaolin is suited to this filler application because it absorbs only moderate quantities of oil, as well as improving the texture of the ink through its platey structure.  Precipitated silica and PCC are also used as extenders but can cause viscosity variations and are more difficult to disperse within ink.

Delaminated kaolin has become more widely used in recent years as it contains a higher proportion of separated plates than water washed kaolin.  This means that delaminated kaolin is better at preventing ink from flowing into paper as it blocks more pores in the paper matrix.

Calcined kaolin has excellent light scattering characteristics but all but the finest grades are too abrasive for use in high volume printing applications.  Engelhard produce grades of kaolin with particle sizes that have increased hydrophobic and better wetting characteristics.  Imerys also produces a range of kaolin extenders for use in inks.

Gravure inks are the main market for extenders within the ink industry.  This is because these liquid inks can have higher extender loadings as the need for active colorants is marginally lower and the ink dots sizes used are thicker than other inks.  Gravure ink is manufactured by mixing aluminium silicates (kaolin) with a resin binder to produce a concentrate containing 50% to 60% extender.  The concentrate is then mixed into the colorant base in achieve the required ink characteristics.  This process allows the kaolin to extend the colorant and provide thixotropy to sharpen dot resolution.  Normal gravure inks contain between 5% to 15% kaolin by weight.

Flexographic inks usually contain similar extender levels to gravure inks.  Kaolin used in these inks is usually of a higher brightness than that used in gravure inks, as the whiteness of the extender pigment is more important than holdout.  In general, the more vivid the colour of the ink required the greater transparency is required from the extender pigment.  In packaging inks, water based ink must have a high holdout as it used in conjunction with porous newsprint.  This allows higher extender levels to block the pores in the paper.  Producers offer specialist surface treated kaolins that wet fast then disperse for use in water based flexographic inks.