P3D Re: Importance of lens coatings

[George Gioumousis <georggms@xxxxxxxxxx>]

K.Morcus wrote
> 
> possible other reason why the cotton buds became blue. Suddenly I
> remembered that I had  used several days ago a black writing marker (one
> uses them for writing on plastic sheets for the overhead-projector) in
> order to make  2 tiny scratches on the front lens rings less visible.
> The marker was of the "non-permanent" type, so the ink was solvable in
> water. But the ink was black not blue. I immediately took the marker
> and  diluted a tiny bit of the black ink with a cotton bud, result:
> BLUE!!
> 
Speaking now as a fallen former chemist, it is very hard to make a
black dye. The problem, I think, is that any molecule with so many
energy levels that it absorbs at all frequencies (like charcoal) 
will be so big that it won't be soluble. The solution is to mix 
several dyes.

An interesting experiment is to put a bit of color on absorbent
paper, then wet the paper from one side so that the color runs.
The dyes often run at different rates, so you can see the
constituents. Even more fun is to spread the colors with one
solvent, let it dry, then use a different solvent to spread
them at right angles.


                           Fallen                Fallen
George Gioumousis           /---\        |       /---\ 
                             o o         |       o o  
georggms@xxxxxxxxxx           |          |         |   
(650) 494-6276              \===/        |       \===/ 
                           Chemist               Chemist


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