Series editors' preface - Wood Tools

Table 5.3 Pigments – continued
Other materials and structures 227
Colour/group Chemical composition Origin/date Properties Refractive
Pigment and description Index
name
Phthalocyanine
green
Blue
Azurite
(mountain
blue)
Blue bice
Ultramarine
– natural
Ultramarine
– synthetic
(French
ultramarine)
Smalt
Indigo
Cobalt blue
(Thénard’s
blue)
Cerulean
blue
Prussian
blue
Chlorinated copper phthalocyanine.
Similar to phthalocyanine blue
A basic copper carbonate
(CuCO 3.Cu(OH) 2). Crystalline.
Appears deep violet blue when
ground coarsely but becomes paler
and weaker in tinting strength if
more finely ground
Artificial basic copper carbonate
similar to azurite. Usually more
rounded and finer particles than
azurite
A mixture of lazurite with calcspar
and iron pyrites. Clear, often
slightly purplish, blue crystalline
particles of irregular size and
shape. A few orange-red particles
of iron pyrites are often seen with
white crystalline calcite
Chemically identical to natural
ultramarine. A compound of
sodium, silica, aluminium and
sulphur. Two distinct kinds of
ultramarine are made: soda
ultramarine and sulphate
ultramarine. It is possible to arrive
at many subtly different shades
according to the method of
manufacture and the exact formula
which can vary from Na 8A l6Si 6O 22S 4
to Na 10A l6Si 6O 24S 2. Finely divided
homogeneous particles usually
smaller and more rounded than
those of natural product and
lacking calcite and pyrites
Formed from cobalt blue glass
coloured by the addition of cobalt
oxide formed by roasting cobalt
containing minerals. Coarser
particles give deep rich purpleblue.
Finer particles only a pale
blue. Very characteristic coarse
glassy fragments
Blue vegetable colour used as both
a dye and a pigment. Appears as
intensely blue discrete particles at
high magnification (1500)
Cobalt aluminate (CoO.Al 2O 3). Pure
blue rounded particles, moderately
fine and of irregular size. Bright
blue by transmitted light
Cobaltous stannate (CoO.nSnO 2).
Finely divided rounded particles,
high refractive index, green blue in
transmitted light. Harmful
A complex compound, technically
ferric ferrocyanide Fe 4(Fe(CN)6) 3.
Available commercially
from 1938
Natural pigment derived
from the mineral
azurite. Important from
the fifteenth to the
seventeenth centuries,
now rarely used
Used extensively in
medieval painting until
the end of the
eighteenth century
Obtained from the
semi-precious stone
lapis lazuli. First occurs
as pigment in sixth and
seventh century wall
paintings. In wide use
until the early
nineteenth century. Still
available
In commercial
production from about
1830
Used in Europe from
the late sixteenth
century (earlier in Asia)
until the beginning of
the nineteenth century
when it was replaced
by cobalt blue and
artificial ultramarine
Obtained from plants of
the genus Indigofera.
Very early use in Far
East. First synthesized in
1880
Discovered in 1802.
Expensive and therefore
liable to adulteration
and substitution
Known early in the
nineteenth century but
not commercially
available until 1860
Earliest of ‘modern’
pigment colours first
Mostly used in tempera as it
appears dark and ‘muddy’ in oil.
Generally very stable but may
discolour in contact with alkalis
and can turn to green Malachite by
hydration
Once used in large quantities as
cheaper, but less stable substitute
for Azurite and Ultramarine.
Tendency to turn green over time
Light-fast and stable under all
conditions except in the presence
of acids when it loses colour and
evolves hydrogen sulphide gas.
Ultramarine in oil may decolour
and become grey with age due to
presence of acids in the oil film.
Ultramarine containing free sulphur
may cause darkening when mixed
with lead or copper pigments.
Soda ultramarine contains a high
percentage of silica and is
sometimes called acid resisting.
Sulphate ultramarine has a greenish
tinge and lower covering power
Stable but with very poor hiding
power
Fair tinting strength. Can be used
in oil but better in tempera or
water colour. Very stable in
tempera and resistant to fading by
light but not when used in thin
films
Light-fast, very stable and
permanent in all painting
techniques
Stable and inert, unaffected by
light or strong chemicals
Transparent but with high tinting
strength. Fairly permanent but
1.40
1.73–1.84
1.72–1.74
1.50
1.50
1.49–1.52
1.74
1.84
1.56
continued