Talbott on thu 22 may 97
Looking at a cone/temp/color chart I was wondering a little about the
technical side of the colors emitted by the heat from a kiln at various
temperatures... Does anyone know if these colors starting at red, orange,
yellow, white heat and moving up the scale to "dazzling white" at cone 16
(I believe?)... What colors, if any, would follow dazzling white?
1ST ANNUAL CLAYARTERS' GALLERY - NAPLES, MAINE (Summer 1997)
http://fmc.utm.edu/~dmcbeth/cag/naples.htm
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Gavin Stairs on sat 24 may 97
At 11:02 PM 22/05/97 EDT, you wrote:
>----------------------------Original message----------------------------
>Looking at a cone/temp/color chart I was wondering a little about the
>technical side of the colors emitted by the heat from a kiln at various
>temperatures... Does anyone know if these colors starting at red, orange,
>yellow, white heat and moving up the scale to "dazzling white" at cone 16
>(I believe?)... What colors, if any, would follow dazzling white?
Blue, and then violet, and even UV, x-rays and gamma rays. What is
happening is that the peak of the (black body) emission spectrum shifts
toward the short wavelengths (higer energies) with increasing temperature.
The peak gives the dominant color that you see. When the spectrum looks
white, it is centered, more or less, in the visible spectrum, around green
or yellow, and we see mostly white. Our eyes are apparently adapted to the
solar spectrum, so sunlight appears more or less white. This shift goes by
the name of Wien's Law, after the guy who worked out what was happening.
You can see the blue color in some stars. However, this is rarely visible
here on earth, except in electric arcs. Arc welders, some cutting torches,
plasma arcs, xenon arcs, and such give off appreciable ultra-violet
radiation, which is why you need protective glasses while welding. The sun
also gives off appreciable uv, which is why we suntan and sunburn. The
color of the kiln fire is quite a lot below this, so uv protection is not
generally required when looking into a kiln. Welders get a particular kind
of eye burn called a weld flash if they get an overexposure to uv from the
arc. This is a uv burn in the eye. A severe weld flash on the retina can
induce permanent blindness, usually in a small spot or line tracing the
path of the weld image on the retina. You can do the same by staring at
the sun, especially during a partial eclipes of the sun, when your eye
opens wide in the semi-darkness, admitting much more of the tiny, bright
light of the hot limb of the sun. Looking into a kiln gives you some uv
exposure, but that is more like looking at a light bulb. The eye closes
down because of the intense light at lower, visible wavelengths, which
affords some protection against the uv.
Gavin
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Gavin Stairs
http://isis.physics.utoronto.ca/
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