Re: Heat Loss

[boblong@xxxxxxxxxxx (Robert Long)]

On Mon, 02 Dec 1996 10:35:51 +0000 (GMT), you wrote:

|But I haven't got the foggiest idea about Bob's laquer and subway light.=
  I
|don't see how a light can change colour depending on how far you are =
from
|it unless the angle of your view of the light changes.  That's how some

That may be a possibility, because whether I walk along the platform
to get a better look at the bulb--which always seems to be on the far
side of the track and, if it can be seen from the platform, just
beyond its end--or view it from a moving train in the dark tunnel, the
actual angle does change.

But the quality changes, too.  At a distance I can only describe the
effect as a "red glint."  Close up, you see a blue bulb.  And I've
never observed anything at close range that would suggest a difference
in color depending on viewing angle.  It just looks like a uniformly
blue bulb.

|But Bob ... what I wasn't sure of was whether you were looking through =
the
|laquer at a light source or looking at it and the red and blue =
colouration
|was reflected rather than transmitted.  The colour change could be an

The lacquer looks black by reflected light.  By transmitted
light--that is, holding the peeled lacquer up to a light source--one
layer looks a sort of dirty deep blue, two layers look even darker
ruby red, three layers look like two except slightly darker, etc.

This suggests poor transmission of a wide band of wavelengths centered
in the blue and very good transmission of a narrow band in the extreme
red or possibly extending into the infrared.  The interesting thing is
that this pattern more or less matches those I've seen in the
spectrographs for many Wratten filters.

Since lamp black is an inexpensive pigment that yields a "cool"--i.e.,
bluish--black (the warm alternative in artist's colors usually is
ivory black), I wondered aloud in e-mail to Hank Hogan whether it
might be the pigment involved.  It also is used to make vinyl
black--or at least is among the pigments used for that purpose in LP
production.  Hank guesses that it may absorb the infrared, whereas I
was wondering whether it could make an effective IR-pass filter for
flash work.  Does anyone know?

|laid down).  Because disc cutting laquers need to have a very homogenous
|structure to avoid noise and have to provide a very flat surface to
|minimise swarf, maybe they were spluttered in distinct layers for better
|control of the hardening.  In this case the individual layers would be =
very

The only lacquer-disc production plant I've been through let us see
everything except the actual application step, which was considered a
trade secret.  My guess would be a spray, but the area on the
production line wasn't big enough for successive spray/dry steps.=20

My observations of the lacquer's filtering properties derive from an
earlier generation of blanks anyway.  My understanding was that it was
sprayed or flowed on.  The bead at the outer edge of the blanks I
regularly dealt with suggested centrifugal flowing.

Bob Long
(boblong@xxxxxxxxxxx)

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Topic No. 5