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Q & A: Mixing Colors

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Most recent answer: 05/20/2011
What colors do I mix to make black
- Anonymous
Something thatís black absorbs all the light of any color that hits it. Regular pigments absorb some colors well but not others- the color you see comes from the light they donít absorb.So you want to mix some different color pigments- say red and blue- to try to absorb as big a range of colors as possible. You may also want to use some dark green or yellow other different pigment to adjust the color if you get something brownish or purplish. You want to use the darkest starting pigments possible, because you need to get all the light absorbed before it has a chance to bounce back out of the surface.
Itís pretty hard to get a good black by mixing regular colored pigments, because these are chosen to absorb very little of some colors of light. Thatís why ink-jet printers usually use separate black ink, with pigments that absorb a broad spectrum of colors, rather than a mixture of the colored inks.

Adam, Mike and Tom

(published on 10/22/2007)

Follow-Up #1: imperfect black: reflection

If black stuff absorbs all the light shined on it then how come if a light shines on a black object you can see a white spot where the light reflects off of it? Isn't all the light absorbed, so how does it still reflect light? And why do shiny black things reflect stuff like mirrors?
- Chris (age 15)
An ideal black surface absorbs all the light that hits it. Since you can see some light bouncing off these real black surfaces, you know they aren't ideal. The shiny ones are particularly interesting. Say you have some sort of lacquer, which forms a nice smooth surface. The lacquer has a different index of refraction than air, more like glass. So its surface will reflect some light just the same way a smooth piece of glass will, making a partially reflecting mirror. Now what happens if you make that lacquer into a sort of black paint, by mixing in some pigment molecules? They will absorb some of the light that reaches them. However, some of the light reflected back before it could reach enough of those absorbers to have a good chance of being absorbed.  So there's still a partial mirror.

Mike W.

(published on 05/20/2011)

Follow-up on this answer.