One possible cause of uneven etching might be insufficient cleaning. Grime
on the glass surface can cause parts of the glass to begin etching only
later because the etching compound had to work through local regions of
"grease-like" "resist"! Persons making high quality optics give a lot of
attention to cleaning. Try scrubbing well and maybe even give the glass a
soak in a moderate strength lye solution (which in itself can attack glass,
but which also destroys grease.) The other proposal to take seriously is
Sandy King's idea that the etching mixture was not well mixed.
When cleaning, after the last rinse notice whether the water wets the glass
with a nice uniform and thin layer. It not, clean some more! It is
probably best to begin etching after shaking off as much rinse water as
possible but before the glass dries, especially if distilled water is not
being used.
Bob
Dr. Robert Mueller
Institut für Festkörperforschung, FZ-Juelich
D-52425 Juelich, Germany
phone: + 49 2461 61 4550 FAX: + 49 2461 61 2610
email: [EMAIL PROTECTED]
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