Calcite Powder or Calcium Carbonate is an inert pigment of considerable bulk, of use in oil painting only as an extender or adulterant. When ground in linseed oil to a stiff paste, it does not retain its white colour, but the paste becomes yellowish brown and forms the familiar plastic cement known as putty. When used with watersoluble mediums, acrylic binders and glue sizes it retains its whiteness: it is invaluable for the manufacture of gesso.