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> NPS Preservation Brief 28
Painting Historic Interiors >
Constituents of Historic Paint: Pigment, Binder,
Paint is a dispersion of small solid particles, usually crystalline,
in a liquid medium. Applied to a surface, this liquid has
the special quality of becoming a solid, protective film when
it dries. Paint also enhances the appearance of surfaces.
A late Victorian writer observed that the coming of a painter
to a house was cause for celebration. Indeed, these statements
not only indicate the chemical and physical complexity of
paint, but also its emotional impact.
Pigment made the paint opaque, thus preventing deterioration
of the substrate caused by ultraviolet light, and added
color, thus making the paint attractive. White lead, a whitish
corrosion product of lead, was most often used to provide
opacity. The white pigment in a colored paint is often called
the "hiding" pigment. In addition to preventing
the sun's damaging rays from hitting the surface of the
substrate, the white lead also helped prevent the growth
of mold and mildew. Not until early in the 20th century
was a successful substitute, titanium dioxide (TiO2), patented,
and even then, it did not come into prevalent use by itself
until the mid-20th century (earlier in the century, titanium
oxide and white lead were often mixed). Zinc oxide was used
briefly as a hiding pigment after 1850.
Early tinting pigments for house paints consisted of the
earth pigments — ochres, siennas, umbers made from
iron-oxide containing clay — and a few synthesized
colorants such as Prussian blue, or mercuric sulfide (crimson).
From the early 1800s on more pigments were developed and
used to offer a wider and brighter variety of hues.
The most common binder in interior paints was, and still
is, oil. Chalk was sometimes added to waterbased paints
to help bind the pigment particles together. Other common
binders included hide glue and gelatin.
The fluid component was termed the vehicle, or medium,
because it carried the pigment. Historically, vehicles included
turpentine in oil paints and water in waterbased paints,
but other vehicles were sometimes used, such as milk in