This months extract is from "Certain-teed Paints Varnishes" a booklet, dated
December 1928, published by Certain-teed, a St. Louis, Illinois, USA paint
and varnish manufacturer. This extract shows what was described and
classified as paint 75 years ago. Of particular interest is the distinction made
between paints and enamels and the fact that the only coating using water as
a solvent was calcimine!
Next instalment: What is calcimine? Descriptions,
recipes and properties from literature of the time.
General Classification and Definition
The term "paint" is generally understood to mean an opaque,
colored, intimate mixture of dry compounds with liquids in a form
which can be used to give protection or decoration to surfaces. The
dry compounds are known as pigments, the liquids, as vehicles. Paint
is said to consist of two main portions, pigment and vehicle.
The functions of the pigment portion are: to obscure or hide by
means of its opacity; to impart color by means of its selective light
reflection; to impart durability to the vehicle by filling up the pores of
the film.
Opacity or hiding and color are imparted by the hiding
pigments. These are sometimes called active pigments for the reason
that they have active tinting strength. The word "active" has another
meaning, however, implying chemical reactiveness between the vehicle
and the pigment. In order to avoid confusion, we shall use the word
"active" with the latter meaning in this book.
The hiding pigments are divided into: the white opaque
pigments, such as white lead, zinc oxide, lithopone; inorganic
chemical pigments, such as the lead chromate yellows and Prussian
blues; the fume blacks, such as lamp black and carbon black; the
earth pigments, such as yellow ochre, the siennas, and red oxides; the
organic pigment dyes, such as red toners and lakes.
Durability is imparted in varying degrees by the hiding pigments
as well as by the non-hiding, non-opaque, inert pigments which are
used to strengthen the film only. The word "inert" will be used in the
sense that no tinting nor hiding strength is implied.
Summing up; we have two main classes of pigments, the hiding
pigments which are opaque and which impart color, and the inert
pigments which are not opaque and which impart no color.
The above paragraph applies only to paints which have an oil or
varnish vehicle, i. e. products commonly known as paints. The inert
pigments rnay have opaque or hiding properties when they are
combined with water as a vehicle in so called water paints or
calcimines.
The function of the vehicle is: to permit application of the
pigments to the surface; to combine with the pigments so as to form a
durable, adherent coating upon the oxidation or evaporation of the
vehicle. The vehicle oxidizes or evaporates according to its nature and
constitution. If the vehicle contains drying oils, they harden by
oxidation; if volatile ingredients are present such as thinners and
water, they evaporate leaving behind oils, gums, or pigments to hide
and protect the surface. All of the types of varnishes which have been
described, the drying and semi-drying oils, and the volatile thinners
may be used as vehicles either alone or combined. Water in any
quantity is used as a vehicle only in calcimine.
Intimate combination of pigment and vehicle is usually
accomplished by means of pressure in the various types of paint mills.
However, calcimines and some forms of oil paint such as aluminum
paints are made by simply stirring pigments and vehicles together.
Mixtures of pigments and vehicles are classified with reference
to their hiding properties into paints and enamels. The former contain
greater amounts of pigments and have better hiding than the latter.
Enamels are usually made with a bodied oil or varnish vehicle as
distinguished from paints which are usually made with a raw oil
vehicle.
Paints and enamels are classified under glossiness, into gloss,
semi-gloss or eggshell, and flat; under exposure, into exterior and
interior; under adaptability, into house paints, floor paints, metal
paints, marine paints, motor car enamels, decorative enamels, and so
on; under Manufactured Form, into paste and ready mixed; under
Method of Application, into brushing, spraying, and dipping; under
Method of Drying, into baking and air drying.
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