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CHEMISTRY
Fabrics and other substances were stained in the beginning with fruit juices, flowers and other
vegetable sources of colouring. A blue was obtained from the indigo plant’s leaf juice.
Besides, various small shellfish yielded a colourless fluid when crushed. After exposure to
air, this turned purple and became Tyrian dye. Sepia, a dark brown dye was obtained from
the ink of the cuttlefish. From the root of the madder plant, a red was obtained. However, a
better source of red was later fond in the female of the insect called “Cochineal”. The
stigmas and styles of the safflower (saffron ) and the yellow locust, logwood, and old fustic
supplied the yellow dyes. The chemistry of nature supplied all these natural dyes, which
were then transferred by man to materials mainly by simple contact, which was by staining.
The dyes thus used may or may not have penetrated the fibres of the material to which they
were applied and they were also affected by sunlight, moisture etc.
Manganese mixed with sodium hydroxide and a few crystals of sodium nitrate or potassium
nitrate produces sodium manganate or potassium manganate when heated. Dissolving the
residue in water gives a green solution. If you blow your breath through a tube in this
solution, it turns red first, the violet.
Carbon dioxide in your breath has turned green
manganate into purple manganate.
Copper sulphate crystals dissolved in water produce a blue solution. If you add a few drops
of ammonia, a light blue precipitate of copper hydroxide appears. If you add more ammonia
and stir the solution, it becomes a deep azure blue.
Produce a dry powder by heating copper sulphate crystals. Add to a drop of water and the
powder will become blue.
Dissolve cupric chloride (copper salt) in a small amount of water and the solution becomes
yellow. Add more water and it becomes green. Add still more water and it becomes blue.
Dissolve chrome alum (potassium chromium sulphate) in water and it is bluish-red. Heat to
70 degrees C. and it becomes green.
Dissolve potassium bichromate in water and the solution appears red-orange.
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Add, drop by drop, a solution of potassium hydroxide or potassium carbonate. It turns yellow
after a while, as the potassium bichromate has been changed to potassium chromate.
Iodine changes colour when heated. Red iodine and white starch produce a blue.
The coal tar chemical industry is based on changing the structure of chemical compounds.
When we change the structure of a substance, its power to absorb light is altered and it
changes colour. Aniline dye manufacture and coal-tar manufacture were introduced about
100 years ago. In 1828 Woehler made the first organic compounds. Coal tar comes from the
distillation of bituminous coal.
Aniline dyes are derived from nitro-benzene, which is
produced by action of nitric acid on benzene. These colours result from complex compounds
of carbon with other elements such as hydrogen, nitrogen, oxygen and sulphur.
Most
dyestuffs in this class come from such colourless hydrocarbons as naphthalene and anthacene
(solids) and benzene, toluene and xylene (liquids).
Organic chemistry deals with carbon compounds. Over 2,000 individual colour compounds
built around carbon are in constant use. Only about 100 colouring matters derived from any
other elements are used.
Sodium chloride – common table salt – provides pure sodium and chlorine for the dyeing
industry. Salt exhausts the dye (causes the colour to affix itself in full strength).
Eosin results from the action of bromine on fluorescein. It produces a red rose colour used in
silk dyeing and in cosmetic manufacture, among other industries.
Combined tannic acid, gallic acid, ferrous sulphate, hydrochloric acid and carbolic acid are
used to prepare standard ink. The material from which a fountain pen is made can affect the
colour of the inks used. Most ink stains can be removed with an alkali, such as ammonia.
The black of carbon paper is a combination of carbon, or gas black, wax, kerosene, oil and
rosin. Coloured carbon paper is produced from an aniline dye and some fatty acid – either
stearic or oleic acid.
Soap dyes are alum for white, ferrous sulphate for red and copper for green.
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Dyes for rubber goods include lithopones for white, antimony sulphide for red, iron oxide for
yellow and red, litharge for black and white lead for grey.
Some Easter egg dyes were said to contain arsenic or lead, which is poisonous. Such dyes
can smell like varnish or paint.
If dry skins of red or yellow onions are put into boiling water with eggs, the eggs take on a
deep mahogany colour.
Carmine yields the colour orange, crimson and scarlet and this is a natural dyestuff. It is
obtained from the female cochineal insect, found in Mexico and Peru. In 1518, the Spaniards
found it being used in Mexico and the insect was later cultivated in Spain and Algeria. The
insects are brushed from cactus plants on which they live and they are killed either in hot
water or by exposure to the sun, steam, or heat of an oven. The method employed affects the
final colour. Natural carmine has been almost entirely replaced by synthetic dyes.
When an insufficient or incorrect mordant has been used, dyed material fades. In these cases,
water, air and sunlight restore the substance to its original structure and cause it to loose
colour.
Dyes are widely used to colour foods. There are synthetic and natural food dyes. Some
natural and harmless food dyes are:
SAFFRON:
(Orange and yellow) - Produced from the dried stigmas of the
safflower. Used from ancient times.
ANATTO:
A reddish dye from the pulp around the seeds of a tropical tree (Bixa
Orellana) used to colour butter, cheese, rice and soup.
PALM OIL:
(Orange) - From the pulp of seeds of oil palm used in colouring many
food preparations. It can be bleached with sodium bichromate and
hydrochloric acid to produce lighter colours.
When properly made, the following synthetic food dyes are harmless:

Naphthol yellow S, yellow OB, ponceau 3R, Orangel, amaranth, tartazine, guinea
green B, eythrosine, indigo disulphonic acid, etc.
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They following synthetic colours have been used in foods, but have been forbidden under
pure food laws:
METALLIC:
Compounds of antimony, arsenic, cadmium, chromium, copper,
mercury, lead, zinc.
VEGETABLE:
Gamboge (yellow), a gum resin. Used in medicine as an emetic or a
cathartic.
COAL TAR:
Pictric acid (carbazotic acid), Victorian yellow (Dimitrocresol),
Manachester yellow ( a derivative of naphthalene), imperial yellow
(aurantia) and Aurine (rosolic acid).
Butter yellow is a coal-tar colour. As it consists of dimethylamino-azobenzene, its use in
colouring cosmetics is forbidden by the Food, Drug and Cosmetic Act. It is known to possess
carcinogenic properties.
The Food and Drug Administration lists the follow coal-tar dyes that are certifiable for use in
foods, drugs and cosmetics, subject to certain general qualifications. These dyes, designated
by numbers in the catalogue of specifications, are brilliant blue FCF, indigotine, guinea green
B, light green SF yellowish, fast green FCF, orange I, orange SS, ponceau 3R, amaranth,
erythrosine, ponceau SX, oil red XO, naphthol yellow S, naphthol yellow S-potassium salt,
yellow AB, yellow OB, tartrazine, sunset yellow FCF.
The following is an example of a specification:

Naphthol Yellow S (FD and C yellow No. 1)

Disodium salt of 2,4-dinitro-1-naphthol-7-sulfonic acid

Volatile matter (at 135 degrees C.) not more than 10.0%

Water insoluble matter not more than 0.2%

Ether extracts not more than 0.1%

Chlorides and sulphates of sodium not more than 5.0%

Mixed oxides not more than 1.0%

Martius yellow not more than 0.03%

Pure dye (as determined by titration with titanium trichloride) not less than 85.0%
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No-one knows when man first made paint. Evidence was found in the caves in France and
Spain that man had been mixing coloured earth with animal fat and applied it to rock walls to
paint representations of animals more than fifteen thousand years ago. We still mix coloured
earths with oil to make some paints. Early man effected four colours - black, brown, red and
yellow. There seem to have been only about six colours in use about 2500 BC. Today there
are several hundred different coloured paints available, although it has been estimated that
only 12 to 18 colours are used by the majority of painters.
There are two large groups of colours:
1. those produced from minerals or other inorganic matter, such as earths and clays, and
2. those produced from animal, vegetable or chemical dyes.
Various methods of manufacture and ingredients are being or have been used to produce
certain colours. However, except for earth colours, most colours are made with synthetic
dyes nowadays.
Pigments are insoluble particles that are held together by, but never become part of, the
medium or vehicle (oil, etc). On the other hand, dyes may in the chemical process become a
part of the medium as chemistry effects changes in molecular structure. Pigments may be
prepared chemically or procured simply from the source. Natural pigments are removed from
the material in which they are found - they appear as finely divided, insoluble, coloured dry
powders in an early stage. The powder is pounded, ground, sieved, heated and treated in
various ways to remove impurities and refine it. The temperature at which it is “burned”
influences the colour that it ultimately makes. The powder is eventually mixed with a
medium to bind it. Olive oil, linseed oil, copal oil, poppy oil, wax, mortar, glue, glycerin,
resin, etc. are some of the mediums used. The mixture is thinned as desired after the grinding
is completed.
White
One of the most useful colours is white as it is not only used alone, but is also the backbone
of most of the tints under various names. White paint is derived from lead, zinc, barium,
lithopone, titanium, antimony, alumina, calcium carbonate, calcium sulphate, kaolin, gypsum,
asbestine, silica, etc. Some of these substances are more useful as extenders or adulterants
than as bases and they may be included with a more substantial base to lower the cost.
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Whites with a lead base are flake white, Kremnitz white and silver white. White lead was
known and used by the Romans and the Chinese more than two thousand years ago. Because
it has a substantial element-resisting body, it is still very extensively used. Metallic lead
“buckles” are corroded by acid in the manufacture of white lead. The buckles are reduced to
a white powder by corrosion in about three weeks. The powder is then washed, dried and
ground. A medium is added and the grinding is continued until the product is satisfactory.
Most paints with a lead base are poisonous and should not be used for furniture or the inside
of a house. Artists who use lead paints should not put paintbrushes into their mouths. White
lead is affected by some gases and by light and may turn yellow and then black through time.
It is not compatible with the copper colour emerald green, or with the sulphur cadmiums,
vermilions and ultramarines.
In spite of these limitations, flake white (purified lead
carbonate) has a character of its own and is preferred by many artists who know how to use
it.
Zinc white is not a poison and is not affected by gases or light. It was said to have been
discovered in 1780. However, it was little used before 1850. In manufacture, the metallic
zinc ore is mixed with hard coal and “cooked” at a high temperature. The great heat forms a
poisonous vapour, which is carried away in long pipes. As the vapour cools, it turns to a
white powder, which is then processed in the same way as other pigments.
Chinese white is a name for zinc white watercolour. It is permanent and can be mixed freely
with any other paint. It dries slowly, but becomes very hard.
No pigments can produce pure white or pure black, or any completely pure colours. A small
amount of blue or violet added to white gives it the appearance of greater whiteness.
Black


Ivory black:
Bone black:
From ivory chips charred in a closed vessel.
From bones reduced by heat to powdered charcoal.
Blacks are considered “warm” when produced from ivory and bones because of their
comparatively brownish appearance.

Blue Black:
From the destructive distillation of wine lees.

Lamp Black:
Almost pure carbon - the soot resulting from burning natural gas or
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mineral oils in insufficient air, which causes incomplete combustion.

Vine Black:
Wood charcoal. Carbonised twigs and vines.
Blacks from wine dregs, soot and wood charcoal are considered “cool” because of their
comparatively bluish appearance.


Mineral Blacks: From coal dust, shale, magnetite and graphite.
Davey’s Grey: From slate. Other greys are usually mixtures of various colours,
such as
red, yellow and blue, in various proportions. Also black and white.
Red
Red pigments are produced from metals such as lead, mercury and iron in various forms.
They are also produced from dyes.

Red Lead:
(Oxide) is produced by heating litharge in air. A binder, such as
linseed oil, is added to the dry powder to make paint.

Chrome Red:
Lead chromate. Used as a base for organic lake pigments.

Iron Oxides:
Hematite (ironstone, an iron ore), red ochre (an earthy iron ore), red
bole
(a crumbly clay), etc.

Venetian Red:
From iron oxides (earth colours).

Indian Red:
From iron oxides.
Used by the ancients. It has a purplish
appearance,
especially when mixed with white.

Vermilions:
Red sulphide of mercury. The Romans used it in its natural state.
Produced artificially since the 12th Century. Not compatible with
lead and copper colours. Some varieties can darken with time.

Cadmiums:
(Orange). Sulphide of cadmium.

Madders:
Originally from the purpurin dye, obtained from the root of the
madder
plant. Now almost entirely produced from anthracene (a coal-tar
product).
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
Alizarins:
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Raw earths and lead
colours
added. Not permanent.

Lakes:
The term “lake” applied to all pigments prepared by the
precipitation of
dyestuff on a base or “carrier”.
Substances used as bases are
barium sulphate, zinc oxide, lead sulphate, red lead, litharge, china
clay, green earth, etc. The base may or may not absorb the dye.
Crimson lake is from the dye carmine (from cochineal) precipitated
on an alumina hydrate base. Madder lake is from purpurin dye
precipitated on an alumina hydrate base.

Mars Reds:
Prepared clay stained with hydroxides. Bluish or yellowish.
The iron oxide colours are the most useful. They have a character that is lacking in others.
They have great staining power and are permanent. Reds produced from dyes are artificially
brilliant and are so fascinating that for a pleasant effect they must be used with restraint.
They are especially useful in tints. Alizarin crimson in time may be bleached by yellow
ochre. Rose madder or alizarin crimson painted over vermilion may approximate the red of
the solar spectrum.
Yellow

Ochres:
Natural earth containing iron, mixed with a binder

Chromes:
(Lemon to orange). Chromates of lead, zinc, barium and strontium
(ancient).
(from
the early nineteenth century).

Lemon Yellow: Barium chromate. Considered nearest to spectrum yellow.

Cadmiums:
(Lemon to orange). Cadmium sulphide. Shades and tints depend on
method of preparation. Genuine cadmiums are expensive. Cheaper
varieties produced by inclusion of cadmium carbonate, zinc sulphide
or cadmium selenide.
Not permanent. (From early nineteenth
century).

Aureolin:
Cobalt and potassium nitrate (1861).

Lakes:
Various yellow dyes precipitated on an alumina hydrate base.
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
Mars Yellows:

Naples Yellows: Lead antimoniate or mixtures of zinc white, cadmium yellow and
Artificially prepared clays, stained with iron hydroxides.
light red.
May become dull and greenish.

Gamboge:
A gum resin. Does not mix with some metallic pigments and fades
in light.
Blue

Prussian Blues: (reddish).
Complex ferric Ferro cyanides, discovered in 1704.
Contain
potassium, ammonium or sodium. Tend to turn black and absorb
any colour mixed with them. A green or violet containing this
pigment turns blue in time. Antwerp blue is a Prussian blue diluted
with alumina hydrate, also called Chinese blue.

Ultramarine:
(reddish). Made from natural stone originally, lapis lazuli (from the
twelfth century). Owing to a scarcity of lapis lazuli, the pigment is
now developed from a complex compound of soda, sulphur, carbon
and clays (sodium sulphide and silicate of aluminum). Through
time it becomes opaque.

Cobalt:
Cobalt-aluminum oxide (from the early nineteenth century). By
artificial
light it appears violet. Nearest colour to spectrum blue.

Cerulean:
Cobalt-tin oxide.

Indigo:
From plants found in India originally (ancient). Principally used in
watercolour and as a dye. Present dyestuff is synthetic.
Purple

Cobalt Violet:
Cobalt phosphate (1850). Useful and permanent.

Magenta:
Precipitate of Rhodamine on an alumina hydrate base. Fugitive.

Mauve:
Precipitate of methyl violet on an alumina hydrate base. Fugitive.
Green
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
Viridian:
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Also known as verte emeraude, emerald green. Hydrated chromic
oxide
(1834). Transparent and permanent.

Permanent Green Oxide of chromium. Dull, opaque, permanent.

Terre Verte:

Chrome Greens: Mixtures of chrome yellows and Prussian blues.

Verdigris:
Copper acetate (poison). Known to the Romans.

Paris Green:
Arsenic and copper acetate (poison).
Sienna:
raw,
Natural earths, containing oxides of iron and/or manganese. When
A green earth containing ferric silicates. Weak tinting power.
Brown


Umber:


Ochre:
Bone Brown:

Bitumen:
coal-tar




Italian Pink:
Van Dyke
Brown:
Sepia:
yellowish brown (raw sienna) and when burnt reddish brown (burnt
sienna).
Same as above. When raw, sometimes has a greenish appearance.
Darkens with time.
Clay stained with ferric hydroxides.
Partially burnt bones.
(asphaltum, mineral pitch). Mixture of hydrocarbons dissolved in
or naphtha. Decomposes in sunlight. Never dries.
(pinkish brown). A precipitate of the dye from quercitron bark.
Natural earth containing partially decayed
vegetable matter (Casse earth, Cologne earth). Fades in light.
Dark fluid obtained from Mediterranean cuttlefish. Only used in
watercolours.
Buff is a mixture of yellow ochre and white.
Cream is a mixture of chrome yellow and white.
Mixtures of finely powdered metals or alloys, such as aluminum, copper, bronze, gold, etc.,
with a medium, such as copal or celluloid varnish, produce metallic paints.
By adding asbestos, borax, sodium, tungstate, etc. to oil paints, fireproof paints are produced.
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Paints have been produced from powdered precious stones and minerals in the Orient - pink
from coral; blue from lapis lazuli; silver from crystal and green from jade.
Cellulose paints are derived from nitro-cellulose in acetone or amyl acetate (flammable).
Luminous paints are produced from mixtures of calcium oxide, sulphur, starch, bismuth
nitrate, sodium chloride and potassium chloride. The mixture is heated and ground then held
together with water or varnish. The product is fugitive and requires frequent intervals of
exposure to sunlight for renewal of its light.
Phosphorescent paints are produced by making zinc sulphate radioactive by association with
radium and mixing product with a binder. This may continually glow for two years.
Fluorescent paints are produced from mixtures containing fluorescent minerals. Various
coloured lights will be emitted according to the mineral used, when the product is exposed to
ultraviolet radiations.
The minerals are mixed with non-fluorescing pigments to effect
various colour changes in theatrical work and advertising. Regardless of the colour, a paint
may, under ordinary illumination, if calcite is mixed with it, appear red under ultraviolet
light. Willemite effects green; fluorite effects blue; wernerite effects yellow; hyalite effects
green, etc
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