Chemistry 151
Chemistry and Color
(from an elementary school
perspective)
Electromagnetic radiation
•Light is a form of energy
that travels through space
like a wave and is
characterized by its
wavelength.
Electromagnetic radiation
•Only certain
wavelengths of
light can be
detected by the
human eye.
White Light
•“White” light is actually
composed of all colors in equal
amounts.
Color Perception
•Specialized cone cells in our eyes respond to visible
light and signal color to the brain.
Color Perception
•There are three
different kinds of
human cone cells varying
in their sensitivities to
different colors of
light: blue, green, and
red.
•Leads to trichromatic
color vision.
•Sometimes called long,
medium and short cones.
Color Perception
•Birds have four
different kinds of
cones (one in the UV).
•Dogs have only two (no
green).
Color Perception
•Birds have four
different kinds of
cones (one in the UV).
•Dogs have only two (no
green).
The Bird’s View
Color Perception
•A defect in one of the three
types of cones leads to “color
blindness,” difficulty in
distinguishing colors.
Color Perception
•Objects appear colored when they reflect light of
that color.
•Red cones
respond, signalling
to the brain that
the apple is “red”.
Color Perception
•Adding red, green, and blue light in equal amounts leads
to white light.
•Adding red, green, and blue light in unequal amounts leads
to all possible colors of light.
Red, green, and blue
are the primary colors
of light.
Color Perception
•Pigments are molecules that absorb certain colors of
light and reflect the others.
•The brain integrates the responses of the cone cells
to perceive the pigment’s color.
The yellow
filter absorbs
blue light;
reflects red
and green.
Absorbance of Light
•A
pigment
absorbs
light
complementary
observed.
generally
that
is
to
that
•Absorbance data can be
correlated to the identity
of pigment.
Absorbance of Light
•For example: a purple pigment absorbs yellowgreen light.
Absorbance of Light
Food Coloring Data:
Yellow: 425 nm
(absorbs violet)
Red: 522 nm
(absorbs cyan)
Blue: 610 nm
(absorbs orange)
Absorbance of Light
• The absorbance of light
can be measured with a
spectophotometer.
Absorbance of Light
•The three primary colors of pigments arise from
subtracting out one of the three primary colors of
light.
Magenta pigment absorbs green light.
Absorbance of Light
•The three primary colors of pigments arise from
subtracting out one of the three primary colors of
light.
Magenta pigment absorbs green light.
Yellow pigment absorbs blue light.
Absorbance of Light
•The three primary colors of pigments arise from
subtracting out one of the three primary colors of
light.
Magenta pigment absorbs green light.
Yellow pigment absorbs blue light.
Cyan pigment absorbs red light.
Color Perception
•Adding magenta, cyan, and yellow pigments in equal
proportions leads to black.
•Adding magenta, cyan, and yellow pigments in unequal
proportions leads to all possible colors of pigments.
Magenta, cyan, and
yellow are the primary
colors of pigments.
Primary Colors of Pigments
•Equally adding adjacent pigments leads to the
development of color wheels.
primary colors
secondary colors
tertiary colors
Complementary colors
•Colors opposite each other on color wheels are
complementary colors.
green
cyan
blue
yellow
red
magenta
•Pigments of complementary colors add in equal amounts
to give black.
Complementary colors
Yellow and blue
Red and cyan
Magenta and green
2012: Color Wheels
Primary and secondary colors
are introduced to show that
some colors are made when
mixing other colors together.
Students make their own color
wheels using homemade paint.
Colors in art
•Paints are a homogeneous mixture of a pigment, which
provides color, and a binder, which cements the
pigment to the solid support after drying.
Pigments in nature
•Early artists had primarily
earth tones in their palettes,
many mineral-based.
charcoal
brown ochre
Mineral-Based (Inorganic) Pigments
hematite (Fe2O3 · nH2O) is a source
of red, yellow, and brown ochre
cinnabar (HgS) is a source of
the red pigment vermilion
azurite (2 CuCO3 · Cu(OH)2)
2010: Alien Rocks
Students analyze rock samples from the
newly discovered planet of Zircondrion to
determine if they are similar to Earth
minerals. Analysis includes:
• Color
• Iron? (absorbance of light)
Properties such as magnetism and
fluorescence
• Chemical reactions
Plant & Animal-Based (Organic) Pigments
Indigo
Tyrian
purple
Madder lake
(alizarin)
Common Sources of Pigments
Marigolds
Grape
Juice
Beets
Cochineal
Beetles
Walnut hulls
Kool-Aid
CH112: Color Activity
Learning Goals:
•Investigate the interaction of
dyes with different fabrics.
•Identify ionic and polar groups
in dyes and fabrics.
•Identify the different types of
bonding interactions between
dyes and fabrics.
The chemistry of fraud detection
History of blue pigment use
Pigment/Metal
Azurite/Cu
Ultramarine/Al
Prussian Blue/Fe
Synthetic Ultramarine/Al
Cerulean Blue/Co, Sn
Manganese Blue/Mn
Dates in use
until 1800
until 1828
post-1704
post-1828
post-1850
post-1935
2008: Art Fraud Activity
Alfredo Fettuccini
1600 - 1650
Last Friday, a priceless masterpiece was
stolen from the little-known Waterville
Museum of Old Weird Art. The painting
was the masterpiece of the great Italian
finger painter, Alfredo Fettuccini.
However, yesterday the caretaker told
police he forgot he had taken the painting
home to clean it, and found it in his
bedroom the next morning. An original
painting by Fettuccini and the painting
produced by the caretaker have been
confiscated, packaged, and sent to the
Colby Chemistry Lab for analysis.
The case of the missing masterpiece
You suspect that the caretaker, Ebenezer
Wheezingeezer, stole the real painting
and replaced it with a fake. You will
investigate the pigments used in the
paintings and then look for clues on the
paintings themselves. The Waterville
Museum of Old Weird Art has granted
you special permission to handle these
rare paintings. The police are standing by,
awaiting your judgment.
Ebenezer
Wheezingeezer
1950 - ????
The case of the missing masterpiece
Experiment 1:
Absorbance spectra of the following pigments:
Pigment from the “Masterpiece” Ebenezer found
Pigment from a modern painting
Pigment found on the floor of the museum
Pigment from a preserved brush of Fettuccini
Pigment stain found on Ebenezer’s overalls
The case of the missing masterpiece
Experiment 2:
Chemical reactivity of the pigments:
pH
Reaction with aspirin
Reaction with potassium hexacyanoferrate(II)
Tests
for Fe
The case of the missing masterpiece
Experiment 3:
Examination for possible restoration:
Fluorescent paint detected with UV light