GEM-SET

Daily Digest Archive for August 22, 2003

Q: (Initially posted on August 14, 2003) FROM MENTEE ALEXIS K. IN VA
How does multicolor, glittery enamel paint function? For example, in car
paint, the color of the car might look one sparkly color and then from
another angle look like another color. Also in nail polish, each angle
reflects a different color. I noticed that you can never see more then one
color at a time. Why is that? Also is there a relationship between
multicolor, sparkly enamel pain and holograms because they too look
different from different angles and you can never see more than one thing at
the same time. What is the process for making holograms and what is the
process for making enamel paint that all this color and image diversity
occurs? Is this a visual trick that fools the mind, or is there really
different stuff that the eye is perceiving or both (or something else). I
can't figure it out by looking at the paint and holograms but am fascinated
with this. My sister brought home a dead beetle the other day and the
underbelly was exactly like a multicolor nail polish I have. Looking at the
beetle from different angles did exactly the same thing that my nail polish
did. Do you suppose that the idea for the paint came from nature and is the
chemistry the same for the paint as it is for the beetle (or similar)? This
is a lot but it is an interesting mystery to me and I could use help
figuring it out.

August 22, 2003
A: FROM MENTOR AMY MCMILLAN IN NY

Alexis, I thought I might add that many iridescent insect colors are
structural and can be produced by light scattering, interference or
diffraction.
The surface structure of the insect cuticle or scales (in
butterflies) either scatters light waves - if the surface irregularities are
large with respect to light wavelength the reflected light appears white.
Many white butterflies have this property. If the irregularities are really
small then the wavelengths of the shorter, blue light is reflected but the
others aren't (this is called Tyndall scattering and produces blues and
greens). Blues of dragonflies are produced this way.
Interference happens when there are several reflecting surfaces
(like scale or cuticle layers) each with different reflection properties
that either cancel each other out, color-wise, or reinforce and act together
to create colors. These are the colors that look really different if you
view them from different angles, because the reflective patterns differ
depending on angle. These colors are very common in butterflies, the blue
of the Morpho butterfly is produced this way by interference effects of
layers of reflecting surfaces. In some Scarab beetles the cuticle is
layered and each layer is a slightly different orientation, which gives it
optical properties of interference of specific kinds. Golds are produced
this way...as well as many greens, blues, bronze, etc.
Diffraction works by surface structures that cause light to split
certain ways - some Staphylinid beetles are brightly iridescent in bright
light but appear black or brown in dim light. Some Scarab beetles and
butterflies look iridescent in one direction but not the other... these are
all surface diffraction patterns.
How that relates to your fingernail polish, I can only guess, but I
thought you might like to hear about how insects do it! Much of what I
wrote came from "The Insects", 3rd Ed., R.F. Chapman, 1982, Harvard
University Press. There are many more resources available about insect
color!
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August 19, 2003
A: FROM MENTOR JOAN LUSK IN RI
What a lot of really interesting questions! I found this site:

http://www.colorshift.com/index.phtml?s=Technical which seems to be a company that makes the paint for Ford cars. They have an on-line color simulator showing a car with various color-shifting paints ("Officer, the car that hit me was red coming at me but blue while it sped away!") And a diagram "Color by Physics" showing the different wavelengths of light reflected at different angles. The technical documents posted on the site go into more details of the pigments and reflective aluminum in the paint - but a lot of the details must be proprietary information.

Holography is something different.
http://members.aol.com/gakall/holopg.html I think the color changes you mention must be "multiple channel holograms" - defined on this site. Frankly I can't explain but I hope the site will help you! This site http://www.abdn.ac.uk/physics/px2010/int.pdf says that the iridescent colors on beetles and feathers are forms by interference between light waves and tells you a lot about the physics involved.

What remains for you is to put all the information together - what exactly are the similarities and differences, and what objects get their color by which methods. I bet most of us wearing nail polish didn't know we were using that much physics for decoration!

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August 18, 2003
A: FROM MENTOR .SALLY RAMSDELLIN KY
Regarding your questions about paint which appears to change color, there
are several technologies. The most common is to use flakes of mica or
metal (such as aluminum) in the paint which act as prisms and reflect light
differently to cause the effect. Another method controls the density of the
paint which is like 1-2-3 Jello and separates on its own into different
layers which reflect differently.

Holography is totally different. It is the projection of a stereo image
onto a translucent medium, so you see the image in 3D based on the
convergence within the medium.

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