Great question! Why is that gold is… well gold,
while most other metals, like aluminum, are grey?
This is a complicated question that has a very
complicated answer, but I'll try to explain the
Let's begin by reminding ourselves that white
light is composed of all the different colors of
light put together: red, orange, yellow, green,
blue, indigo, violet, and every color in between.
When sunlight reaches the Earth it is composed of
all of these colors; in other words, sunlight is
white light. When the light hits an object, the
object can either absorb the light or not absorb
the light. In general, the absorption of different
colors is not equal, meaning that an object will
absorb specific colors of light and not absorb
When sunlight interacts with a piece of gold,
the gold tends to absorb blue light and not absorb
green and red light; instead, the green and red
light is partially reflected. What we as humans
see is the combination of the reflected green and
red light, which gives the classic golden yellow
In other metals, like aluminum, the colors of
white light are almost equally absorbed and
reflected and thus what we see is a silvery,
Hope this helps you understand the basic
Bonus question: Using this same concept,
what color of light do most plants absorb and not
Bonus answer: Most plants are green and
thus they tend to absorb all the colors but green
and not absorb green (i.e. the green color is
reflected, which is what we see!)
Gold is a type of material known as a metal.
Most metals reflect (bounce back) the visible
(white) light that is shined onto their surfaces.
A good example is the metal silver, which is used
in mirrors. The reflection of visible light off of
the surface of silver is the reason that you can
see yourself when looking into a mirror.
Gold is a special metal that both reflects
(bounces back) and absorbs ("keeps") some of the
visible (white) light that is shined onto its
surface. An important idea is that visible light
is called white light because it is made up of all
of the different colors of a rainbow: red, orange,
yellow, green, blue, indigo, violet, which combine
together to produce the color white. See the
following webpage for a picture of a rainbow:
It turns out that the colors that are absorbed
("kept") by gold are the darker colors of green,
blue, indigo, and violet (the bottom part of the
rainbow), while the colors that are reflected
(bounced back) by gold are red, orange, and yellow
(the top part of the rainbow). When these bounced
back, reflected colors all reach your eye, they
blend to end up giving gold the shiny, yellow
appearance that is so familiar (as long as the
gold is clean and polished!).
Thanks for your great question, and please feel
free to send more excellent questions our way!
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