Questions:

a) Which of the listed paints would have contained iron oxide?

b) Which would have reflected light with a wavelength of 560 nanometres?

a) Red ochre: ochres are "native earths" containing iron oxides and with either a clay or chalky basis. Ochres are widely distributed in beds or pockets in stratified rocks. Some ochres can be made into pigments with a minimum of grinding, others need more preparation. Ochres vary in color from pale yellows to deep reds and browns.

Red ochre contains ferric (iron) oxide: Fe₂O₃ (aka hematite)

b) Chrome yellow and zinc white. The visible light part of the electromagnetic spectrum ranges from wavelengths of 400 to 700 nanometers (nm). The yellow paint would have reflected wavelengths of 560 nm and, the white paint would have reflected most of the visible light wavelengths, including those of 560 nm.

Chrome yellow contains lead chromate: PbCrO₄

Zinc white contains zinc oxide: ZnO

Cobalt blue contains cobalt and aluminum oxides: CoO.Al₂O₃

A nanometer is one billionth of a meter.

660 nm = red light,

560 nm = yellow light,

460 nm = blue light

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Visit some interactive java applet color experiments written by Asso. Prof. Fu-Kwun Hwang Dept. of Physics, National Taiwan Normal University .....

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