What is oil absorption of pigment? Why it is important in paint formulation?

 Oil absorption : how many oil /resin/water require for 100gm of pigment/filler is called oil absorption.

  The most common method is ASTM D 281, "Oil Absorption by Spatula Rub-out." The rub-out of a weighed amount of pigment is made on a glass plate or marble slab as linseed oil is slowly dripped from a dropping bottle or buret. The endpoint is a stiff, putty-like paste that does not break or separate. The oil absorption value is calculated from the weights of oil and pigment used in the test and is reported as the number of grams (pounds) of oil required to exactly wet 100 grams (pounds) of pigment. 

Pigment Oil Absorption Value :

Basic lead carbonate 9-12

Barium sulfate (Barytes) 10-20

Barium sulfate (Blanc Fixe) 15

Calcium carbonate 16-18

Zinc oxide 17-20

Red iron oxide 20

Uncoated titanium dioxide 11

Amorphous silica 29

China clay 30

Phthalocyanine blue 34

Milori blue 51

Lampblack 51

Carbon black (medium) 124

Diatomaceous earth 196

Why oil absorption is important?  

As a paint chemist my experience is oil absorption is important to measure correct CPVC of paint. For the primer formulation its need to use low oil absorption filler. Where porocity is major fact. 

 Glossy paints should have use high oil absorption where fineness / finishes is important. 

The more oil absorption pigments can make Thixotrophy problem. Low oil absorption filler can give rough surface finish which is require for primer or sealer formulation.

So many reasons have for the importance  of oil absorption. 

Thanks