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Hi -

There's another reason to prefer front-surface mirrors in addition to the 
(admittedly marginal) improved reflectivity - it's easier to clean salt water 
off them. When salt water gets in behind a rear-surface mirror, you can't get 
back there to clean it - and it eats the silvering. The trade-off is that you 
need to be somewhat more careful about abrasion on the front surface. Modern 
coated front-surface mirrors, however, aren't as delicate as they seem.

Check the Astra IIIb section of the Celestaire catalog (www.celestaire.com) 
for a brief discussion of front- vs rear-surface mirrors.

Regards,
Bill Arden

In a message dated 10/16/2002 10:28:37 PM Eastern Standard Time, Robert Eno  writes:

>Thanks to all for leads on re-silvering of mirrors.
>
>Now another question (because questions beget more questions):
>
>The general consensus, both on this forum and in navigation texts, is that 
front-silvered mirrors are the preferred option as they provide superior 
performance to that of rear-silvered mirrors.
>
>I am the proud owner of a C.Plath as, I am sure, are many other list members. 
In looking at my Plath, it is apparent that the mirrors are not front 
silvered but are silvered on the rear. Yet C.Plath was (is) the Rolls Royce 
of sextants. That they did not go the whole nine yards by silvering their 
mirrors on the front surface seems incongruous to their high status in the 
sextant world.
>
>Does anyone know why they may not have chosen to go with the front silvered mirrors?
>
>Robert
>

   

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