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Lecture 4

Lecture 4 AK/NATS 1870: Fall Leaf Colour AK/NATS 1870: Colour Contrast (following Itten) 1. Contrast of Hue – strongest given by Y R B 2. Light/dark Contrast – white/black gives most extreme contrast 3. Cold/warm Contrast


Department
Natural Science
Course Code
NATS 1870
Professor
Robin Kingsburgh
Lecture
4

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AK/NATS 1870: Fall Leaf Colour
leaves (in summer) are green because they contain the chlorophyll molecule
→ a pigment that absorbs red and blue wavelengths, and reflects green wavelengths
role of chlorophyll is to absorb sunlight and drive photosynthesis reactions, to provide
energy for plant
in fall (shortened days, cool nights) → chlorophyll production declines → green colour fades
if leave contains carotene pigment → they appear bright yellow
- carotene absorbs BG and B wavelengths
- more stable than chlorophyll molecule
if concentration of sugar in leaf increases, sugar reacts to form anthocyanins
→ red pigment family
- absorb B, BG, G wavelengths
- colour sensitive to pH (acidity) of sap:
acidic – bright red (ripe apples)
less acidic – purple (ripe grapes)
- formed by reactions between sugars + certain proteins in cell sap
→ does not occur until sugar concentration high
→ requires sunlight
(note – tops of trees, side facing south → turn red first)
other leaf pigments: flavones – yellow; tannins – brown
AK/NATS 1870: Colour Contrast (following Itten)
1. Contrast of Hue – strongest given by Y R B
2. Light/dark Contrast – white/black gives most extreme contrast
3. Cold/warm Contrast
Y, YO, O, RO, R, RP – warm colours
YG, G, BG, B, BP, P – cold colours
-in landscape, cold colours tend to recede (used for background objects) while
warm colours tend to come forward (used for foreground objects)
4. Complementary Contrast
-using paints, true complements when mixed give neutral grey, black, (or in real life
often brown)
(in light, true complements when mixed yield ______________)
-painters’ primary complements:
-R – G (=B + Y) → in complements, all 3 (painters’) primaries
-Y – P (=R + B) are present
-B – O (=R + Y)
→ physiologically, the eye requires any given colour to be balanced by its complement,
and will spontaneously generate the complement if it is not present (though process of
_______________)
→ rule of complementary harmony based on equilibrium in eye
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