Series editors' preface - Wood Tools

224 Conservation of Furniture
Table 5.3 Pigments – continued
Colour/group Chemical composition Origin/date Properties Refractive
Pigment and description Index
name
Dragon’s
blood
Madder lake
Alizarin
crimson
Cadmium
red
Yellow
Yellow
ochre
Massicot
and litharge
Orpiment
(King’s
yellow)
Realgar
Mars yellow
Not strictly a pigment. Dark red by
reflected light but clear orange red
by transmitted light
A mixture of alizarin and purpurin,
both anthraquinone dyestuffs.
Usually very fine crimson red
powder
1,2-dihydroxyanthraquinone
obtained from madder root (Rubia
tinctorum). Lake pigment made by
precipitating dye on aluminium
hydrate (Al(OH) 3)
Cadmium sulpho-selenide
(CdS(Se)). Shades varying from
deep maroon to vermilion can be
prepared by varying the ratio of
selenium to sulphur and the
conditions of the reaction. Very
small non-crystalline particles of
very high refractive index
Ochres are natural earths consisting
of silica and clay with colour
(yellow, golden, red or brown)
due to oxides of iron. Colour in
yellow ochre is caused by hydrated
forms of Fe 2O 3.H 2O chiefly
goethite. Usually very small regular
grains. Varies in shade, usually
rather dull golden yellow by
reflected light
Both forms of yellow lead
monoxide PbO. Massicot is dull
yellow, litharge usually contains a
little red lead and is therefore a
little more orange. Fine almost
amorphous texture like lead white
Arsenic trisulphide (As 2S 3). Brilliant
rich lemon yellow in pure form.
Crystalline, occurring in small
flakes and fibrous masses. Coarsely
ground to preserve rich colour.
Surface appears glossy or waxy
Natural orange red sulphide of
arsenic (As 2S 2) closely related to
orpiment and associated with it in
nature
Mars colours are artificial ochres
precipitated from a solution
containing alum and a soluble iron
salt using alkali. This produces a
yellow precipitate of variable
colour depending on the
proportions of alum used. When
heated, the yellow gives rise to
various shades of orange, red,
Dark red resinous
exudate from fruit of
the rattan palm
(Calamus draco)
First isolated in 1826
and first synthesized in
1868. The first natural
dyestuff to be made
synthetically
Prepared by
precipitation from
cadmium sulphate using
sodium sulphide and
selenium. Commercial
production began c.1910
Natural product in early
and continuous use.
Artificial product Mars
yellow is also made
Manufactured pigment
known from antiquity
Natural mineral known
from ancient times.
Once widely used but
now largely abandoned
because of toxicity and
supply shortages
use discontinued but still important
in anti corrosive paints for iron.
Toxic
Soluble in alcohol and other
organic solvents. Has been used
for colouring varnishes but not
much as an artists’ colour. Fugitive
unless locked in a resin film
Natural madder lake fluoresces
under UV light but synthetic
variety does not
Base is finely divided, semitransparent,
inert. Synthetic alizarin
is among most light fast of organic
red pigments but may not be
permanent when mixed with earth
colours
Very good hiding power. Stable,
light resistant popular modern
pigment. Very toxic
Ochres vary in hiding power, that
of yellow ochre is good.
Unaffected by acids and alkalis and
permanent in all techniques
Good hiding power and properties
similar to lead white. Unaffected
by strong light but may revert to
lead white on long exposure to
damp air
Highly refracting with fair hiding
power. Stable to light, air and most
chemicals but incompatible with
some lead and copper pigments
because of its sulphide content
The chemical and physical
properties are similar to those of
orpiment. Considered too
poisonous for modern use
c 1.7
(base)
2.64–2.77
2.0–2.3
2.51–2.71
2.4–3.02
Slightly <
orpiment
continued