Archived posting to the Leica Users Group, 2002/03/03

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Subject: Re: [Leica] Removing lens coating
From: Dr.Alexander.Kraus@gmx.de
Date: Sun, 3 Mar 2002 22:18:42 +0100 (MET)
References: <11e.cb56798.29b3861a@aol.com>

It is true that toothpaste contains polishing agents, but its grain size is
about same as the finest grain size that's use in the optical industry. There
is no other way to remove a lens coating than to polish it off. Vapour
deposited mineral salts (like magnesium fluoride or aluminum oxide) are insoluble
in all common solvents. Maybe it would come off if soaked in concentrated
potassium hydroxide solution, but that would etch the glass surface and make the
lens unusable.
Old coatings are usually much softer than the glass underneath. If you
polish it by hand, it would take *very* long until a significant amount of glass
get grinded off. Just don't use a power tool with 10,000 rpm! I treated an old
Zeiss Sonnar, which had quite severe cleaning marks in the coating, with
toothpaste and had very good success. I couldn't see any negative impact on the
performance.

Alex  


> In a message dated 3/3/02 4:40:46 AM Eastern Standard Time, 
> Dr.Alexander.Kraus@gmx.de writes:
> 
> >  I had good success removing older coatings with toothpaste in the
> >  past. You have to rub a little bit until it comes off, but it doesn't
> seem 
> > to harm the glass.
> 
> I wonder. Most toothpastes contain pumice. That's a grinder/polisher. I
> guess 
> I'm pretty certain it will remove coatings; I wonder if it won't also
> remove 
> glass, i.e. act like a fine polishing agent.
> 
> Seth        LaK 9
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In reply to: Message from SthRosner@aol.com (Re: [Leica] Removing lens coating)