(2) Antimony oxide. This pigment is used chiefly in the manufacture of fire-retardant paint,
where it is used in combination with chlorinated materials and calcium carbonate. The Navy uses paints
with this type of pigment on interior surfaces of its ships.
(3) Zinc oxide. This is one of the finest of all white pigments and actually one of the whitest.
It is opaque to ultraviolet light and, when incorporated in a paint, protects the film from the destructive
action of the ultraviolet rays in sunshine. While zinc oxide contributes to the hiding power of paint,
some of its other properties are more important. It is not discolored by sulfur gases in the atmosphere,
and it is nonpoisonous. Zinc oxide is used as a preventive for mildewing or yellowing and also adds
hardness to a paint film. It is a valuable pigment for controlling checking, chalking, and dirt retention of
exterior paint films. It is also used in metal-protective paint for rust inhibition and in other paints for
greater resistance to scrubbing. There is a current trend to use latex primers in place of zinc-oxide paint
for rust-inhibition work.
b. Color Pigments. Color pigments can be obtained from deposits in the earth's crust or through
(1) Earth colors. The most widely known earth colors in the painting industry are yellow
ocher, raw and burnt sienna, and raw and burnt umber:
Yellow ocher. This color contains hydrated iron oxide as a coloring matter. Various
ochers contain from 10 to 60 percent hydrated iron oxide, the remainder being
siliceous matter or clay. In color, yellow ochers vary from pale to very dark yellow,
almost olive. When of good quality, they are excellent pigments, permanent in color,
and combine well with all paint vehicles as well as other pigments. When used with
white pigments, they will produce fine-cream or buff tints. They are primarily used
as tinting colors.
Raw sienna. This color resembles yellow ocher in general composition, since it is
colored by hydrated iron oxide. It is brownish-yellow in color. When used with
white, it produces cream tints which have greater color strengths than ochers. Raw
siennas are valuable for use as staining and graining colors. However, they are
undesirable for base colors.
Burnt sienna. This color is obtained by roasting raw sienna, thereby producing a
strong, reddish-brown pigment. Burnt sienna is used to a lesser degree than raw
sienna. However, it is a very valuable pigment when used for shading and glazing.
Raw umber. This color is similar in composition to sienna. It has a greenish-brown
color, is permanent, possesses medium opacity, and mixes well with paint vehicles.
Raw umber gives drab tints to white and gives a great variety of other shades when
mixed with color pigments, and it is used extensively for these purposes.
Burnt umber. This color is calcined (roasted) raw umber. It possesses a rich, brown
color that is darker than raw umber and free of redness. Burnt umber is used in
practically all types of paints and stains.