Re: Weddings & IR flash

[boblong@xxxxxxxxxxx (Robert Long)]

On Tue, 20 Aug 1996 09:56:13 +0100, you wrote:

|As for foil to cover a flash with, a #25 red and #47A blue in combination
|make a very sharp chop at 700A. 

How interesting!  Perhaps I can solicit comments on something I've
pondered many times without conclusion, though it's only peripherally
related to IR:

Traveling in the New York subways and looking out the front window of
the train I've often noticed faint "blue" lights in the distance that,
when the train comes closer, turn out to be red lights--so-called ruby
bulbs, which to the eye have a color very similar to a Wratten 25.
(I'm ignorant of the function of these bulbs--perhaps marking
emergency telephones?)

Similarly, if you strip the "black" lacquer surface of "acetate"
recording discs from the aluminum substrate, it looks like a deep-blue
or muddy-indigo filter.  If you add a second layer of lacquer, it
turns into a deep "ruby-red" filter instead.  If you add a third and
fourth and fifth layer, there is very little change.  It remains a
ruby red filter, but gradually grows darker and darker.  (I'm not sure
that this is true of all brands of lacquer recording blanks, but it is
true of any I've tried.)

In this context I might note that I've read that the "ruby red" glass
for stained-glass windows is traditionally created by the addition of
powdered metallic gold--a recipe I find as mysterious as the above,
though there obviously can be a chemical explanation.

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Topic No. 24