Pigment History
Europe
Recipes for blue pigments were mentioned extensively in medieval artists' manuals
The recipes varied from some rather straightforward methods of making copper acetate to more
mysterious "silver blue" recipes for which, as Cyril Stanley Smith has said, "the chemistry
escapes us."
The proliferation of these recipes is understandable in light of the fact that the only two blue
pigments available to the medieval artist (between the eighth and the sixteenth centuries) were
the very expensive azurite and ultramarine (3).
Recipes for making artificial blue colors are very old. They are embedded in the literature of a
technical tradition dating from the 3rd century CE that managed to survive five centuries of "dark
ages" to reemerge in the late 8th or early 9th century in two Latin manuscripts, which contain
recipes for making blue pigments from both copper and silver.
Other blues with intriguing crystalline forms are still unidentified, including a beautiful blue with a
morphology resembling rosettes (Fig. 4). Could it be that the medieval artist was such a good
synthetic chemist that, to this day, we have failed to synthesize and characterize compounds
produced many centuries ago? The mystery surrounding the blue pigments remains unsolved.
an iron, or Prussian, blue (Fig. 5). The iron blues are the first of the artificial pigments with a
known history and an established date of first preparation. The color was made by the Berlin
colormaker Diesbach in or around 1704. Moreover, the material is so complex in composition and
method of manufacture that there is practically no possibility that it was synthesized
independently in other times or places.
**
all paints have three types of components:
Pigments, consisting of small particles of colored compounds
Media, serving to suspend the pigments and bind them to the surface of the object painted
Diluents, allowing the painter to thin the paint to the best consistency for the work.
Pigment, binder or medium, thinners
**
http://cator.hsc.edu/%7Emollusk/ChemArt/paint/pigment.html
Until the mid-Ninteenth Century, most artist's pigments were derived from finely ground naturally
occurring minerals: rocks and ores. Most of the dyes came from organic sources: mostly
plants like indigo for blue or madder root for red but also a few animals like cochineal beetles for
carmine. (Hampden-Sydney's "garnet and grey" colors date back to the Civil War when the
students dyed their civil war uniforms with pokeberries and butternut hickory husks.) With the rise
of modern chemistry in the Nineteenth Century, some new "inorganic" or mineral-like compounds
like "chrome yellow" and many, many new organic dyes were prepared.
Shown below are some examples of a few of the inorganic or mineral pigments used in paints.
Many of these have been in use for centuries.
COMMON NAME
CHEMICAL NAME
FORMULA
COLOR
Cinnabar
Mercury(II) Sulfide
HgS
Vermillion
Cobalt Blue
Cobalt(II) Oxide
Aluminum Oxide
CoO-Al2O3
Bright Blue
Prussian Blue
Potassium Iron(III) Ferrocyanide
KFe(Fe(CN)6)
Deep Blue
Verdigris
Copper(II) Acetate
Cu(CH3CO2)2
Green
Chrome Yellow
Lead(II) Chromate
PbCrO4
Yellow
Burnt Sienna
Iron(III) Oxide
in clay
Fe2O3
Reddish Brown
Malachite
Copper(II) Carbonate
Copper(II) Hydroxide
CuCO3Cu(OH)2
Green
Cadmium Yellow
Cadmium(II) Sulfide
Zinc(II) Sulfide
CdS-ZnS
Lemon Yellow
Rutile
Titanium(IV) Oxide
TiO2
White
Chinese White
Zinc Oxide
ZnO
White
Lead White
Lead(IV) oxide
PbO2
White
Vine Black
Carbon
C
Black
ORGANIC COLORANTS
Among the new organic colorants were the "Azo Dyes" which were discovered by accident by
Perkin in England in 18xx. Perkin had hoped to make a synthetic version of quinine, the only
known anti-malarial treatment which was an extract of a South American tree Because those
countries that were the sources of quinine were in the hands of the Spanish and Portuguese,
English colonists across the topics were vulnerable to malaria. Perkin used coal tar, an ample
and cheap byproduct of the coal and steel industry, to provide as the starting materials for his
experiments. The resulting compounds that he made gave colors more brilliant and varied than
those available from most vegetable dyes. They were also inexpensive so that the average man
could afford colored clothes that had previously been beyond the reach of all but the rich. Though
Perkin himself became rich from his patents, the British did not capitalize on their early
technological lead in dye-making. The color chemistry industry moved to Germany were several
companies, notably I.G. Farber, made huge advances in chemistry and wealth.
Shown below in a skeleton of the common diazo "kernel" that all azo dyes have. It has two
benzene rings (six carbons in a ring with three double bonds) joined by a double-bonded pair of
nitrogen atoms. Shown along with this central piece are several organic dyes that are also used
as pigments in paints. You might try to identify those that are azo dyes.
PIGMENTS.
Most traditional artist pigments are derived from finely ground minerals or inorganic compounds.
(Ultramarine, from "across the sea", is the pigment from ground lapis lazuli, a semiprecious
stone.) Most traditional dyes came from organic sources such as berries and insect bodies. (The
garnet of Hampden-Sydney's colors came from using the juice of the pokeberry to dye their civil
war uniforms; the gray came from butternut husks.) With the advent of modern chemistry, many
colored synthetic organic and inorganic compounds have become available.
The chief class among these, is the group of diazo compounds that became available in the
nineteenth century. Some of these compounds have been used as both dyes and pigments.
Shown below is one of the diazo dyes,
All diazo dyes have benzene rings separated by a double bonded pair of nitrogen atoms. You
should be able to recognize a diazo dye by this substructure.
TYPE OF PAINT
BINDER
DILUENT
DESCRIPTION OF MATERIALS AND PROCESS
Encaustic
Beeswax
None
The Egyptians, Greeks, and Romans often used
beeswax as the medium for pigments. The
encaustic method was in very common use until
the 8th century A.D. and is still used by a few
painters today. In this technique finely ground
pigment is mixed in melted wax and applied to
the surface. Waxes are polymers composed
redominantly of hydrocarbons.
Fresco
Plaster
Ca(OH)2
CaCO3
Water
In fresco painting, the medium and the surface
are the same. An aqueous suspension of the
pigment is applied directly to a wet plaster of
calcium hydroxide and fine sand. The pigment is
absorbed and is bound into the surface as the
plaster dries. Several processes involved in
making a fresco are of chemical interest.
Limestone or marble which is made up from
calcium carbonate is heated in a lime kiln to
produce quicklime, CaO.
CaCO3 --> CaO + CO2
The quicklime is then "slaked" with water to
produce lime, Ca(OH)2, which is used to prepare
the plaster.
CaO + H2O --> Ca(OH)2
As the plaster dries and ages, the calcium
hydroxide in it undergoes a chemical reaction
with CO2 in the air changing it from Ca(OH)2 to
CaCO3, which is the mineral that comprises
limestone and marble.
Ca(OH)2 + CO2 --> CaCO3 + H2O
This calcium carbonate matrix, which now
contains the pigments of the painting, is
insoluble so that the painting is almost
impervious to water.
However, calcium carbonate in all its forms
reacts with sulfuric acid to give CaSO4 which
has a much greater solubility in water than does
aCO3. Thus acid rain, which contains sulfuric
acid, slowly converts the CaCO3 in frescoes and
in marble sculpture to CaSO4. The CaSO4 then
flakes of or washes away eventually destroying
the artwork.
Egg Tempera
Egg Yolk
Water
Until the 15th century, egg yolk was used as the
most common binder and medium for paints.
Egg tempera is prepared from the separated
yolks of eggs mixed with a slurry of artist's
pigment in water. Enough water is added to
provide the proper consistency for painting. This
paint dries extremely rapidly, and when applied
thinly, it gives a translucent glaze that allows
either a white surface ground or an undercoat to
show through. The drying and hardening
process of the medium involves the both the
denaturation of the proteins from the egg and
polymerization of the fats in the yolk.
The proteins form many hydrogen bonds with
each other and with the surface, locking the
pigments into a solid matrix. As they age, these
proteins form covalent bonds with each other,
making the matrix very stable and permanent.
Oil
Linseed or
Walnut Oil
Turpentine
Mineral Spirits
By the 15th century, oil paints, using vegetable
oils as the medium, replaced egg tempera as
the most common paint. The oil most commonly
used is linseed oil which is obtained from the
seed of the flax plant. The oil does not dry but
rather is cross-linked where there are carboncarbon double bonds in the oil. This process is
initiated by oxidation by oxygen in the air or by
metal oxides. Early oil paints were very slow
"drying" because the initiation step of air oxidation is quite slow. However, it was soon discover
that adding some metal oxides like ZnO or MnO2 could also start the cross-linking process and
speed up this hardening process. Ironically, the relative slow pace of drying compared to that of
egg tempera was considered an advantage since paintings could be reworked and the
composition modified before the paint hardens.
Watercolor
Gum Arabic
Water
In water paints the pigments are usually very
finely ground mineral based transition metal
compounds and the vehicle is an aqueous
solution of gum arabic, a resin prepared from the
sap of the African acacia tree. This resin is a
translucent water soluble polymer. The resulting
paintings usually retain a translucent quality;
they appear bright in part because the whiteness
of the paper is reflected through a layers of the
paints. A much more opaque water based paint,
Gouache, has more coarsely ground pigment
and sometimes incorporates CaSO4 as an
opaque whitener. The medium is still gum
arabic.
Acrylic
Acrylate Esters Water
Since 1945, plastic media such as acrylics have
become popular. These man-made media have
not replaced oil paint as the vehicle for pigments
but rather have provided an alternative method.
These paints use an aqueous suspension of
both the pigment and monomers of compounds
such as methyl acrylate and vinyl acetate. The
paint does not become plastic until the
monomers combine. In a process similar to the
"drying" of oil paints, these monomers are linked
together by a chain reaction to form a polymer
molecule that is insoluble in both water and most
organic solvents.
methyl acrylate vinyl acetate