These are the cheap inert materials or pigments, used as adulterants with the base, to extend help in performing the following functions; (as they extend help, so known as extenders).

(i) To reduce the cost of the base and hence of the paints as a whole.

(ii) To increase or decrease the weight of paint, and hence to prevent too rapid setting of the ingredients.

(iii) To help to maintain the other pigments in suspension by modifying the weight.

(iv) To increase the durability of paint.

(v) To improve the quality of brushing.

(vi) To prevent shrinkage and cracking of paint.

However, the extenders possess little covering or hiding power. The commonly used extenders or inert fillers are:

(i) Magnesium silicate,
(ii) Talc,
(iii) Barytes (barium sulphate),
(iv) Calcium carbonate,
(v) Gypsum,
(vi) Ground silica, and
(vii) Diatomite, etc.