Lens problem - fungus??

On 16 Nov, 04:29, krishnananda wrote:
RolandRB wrote:

I would imagine that vinegar kills lens coatings as the coating is

alkaline (as is the glass in lenses).

5% acetic acid can damage glass? I keep my glacial acetic acid (99%) in
a glass bottle with no harm (for mixing stop bath).

Hydrochloric and Nitric acids do not harm glass (both used in etching
and lithography).

There a difference between glass, as used in glass bottles, and glass,
as used in making lenses. Usually, a high refractive index is sought
after in glass for making lenses and this can be achieved by mixing in
metal oxides of various sorts. Metal oxides are alkaline and can be
attacked by acids. For example, I am sure you are aware how lead
crystal cut glasses refract the light in a spectacular way. In this
case lead oxide has been mixed with the silicon oxide that is pure
glass to increase the refractive index to give this effect.

Hydrofluoric acid does damage glass.

I have no idea what damages lens coatings besides abrasion.

Some lens coatings are metals. Such coatings can be damaged by acid
unless these coatings in turn have been given protective coatings to
prevent this happening through normal use.

--krishna

--
jai bhagavan

RolandRB wrote:


Some lens coatings are metals. Such coatings can be damaged by acid
unless these coatings in turn have been given protective coatings to
prevent this happening through normal use.

It would appead from here that caustic cleaning agents are more of a
problem, however, there is reference to problems with an acid version of
windex. Not familiar with that product, as we don't have it over here.

http://www.microscopy-uk.org.uk/mag/...4/cdclean.html

Pete

--
http://www.petezilla.co.uk

Peter Chant wrote:


It would appead from here that caustic cleaning agents are more of a
problem, however, there is reference to problems with an acid version of
windex. Not familiar with that product, as we don't have it over here.

This site discusses use of ammonia, vinegar and naptha.

http://www.prairienet.org/b-wallen/B...TechLenses.htm


--
http://www.petezilla.co.uk

On 19 Nov, 19:54, Peter Chant
wrote:
Peter Chant wrote:
It would appead from here that caustic cleaning agents are more of a
problem, however, there is reference to problems with an acid version of
windex. Not familiar with that product, as we don't have it over here.

This site discusses use of ammonia, vinegar and naptha.

http://www.prairienet.org/b-wallen/B...TechLenses.htm

--http://www.petezilla.co.uk

It doesn't "discuss" it. It mentions the use of ammonia and vinegar.
It would be wise to read it in context as it might apply to pre-coated
lenses.

RolandRB wrote:


It doesn't "discuss" it. It mentions the use of ammonia and vinegar.
It would be wise to read it in context as it might apply to pre-coated
lenses.

OK, poor choice of words. Not trying to start an argument by the way, just
doing a bit of research. However, this is usenet and it is easy to give
the wrong impression.

Thanks for your comments.

I think before approaching diy of this sort you need to weigh up the
options - how much is it worth to fix by a professional, how much to simply
replace and how much will you be annoyed if it goes wrong. I suspect the
price of a repair would go a long way towards a replacement, and a
replacement would likely not have the fine scratches from cleaning like
this one.

Pete

--
http://www.petezilla.co.uk

In message ,
krishnananda writes
Hydrofluoric acid does damage glass.

And bones - never get it on your skin.
--
Paul Friday

Paul Friday wrote:


And bones - never get it on your skin.

Isn't that the stuff that goes through your flesh and destroys the bone
underneath. Nice stuff. Interestingly apparently some of the damage
wrecked by fungus is the fungus excreting hydrofluoric acid. How does it
do it without killing itself?

To lower the tone, you think you've had it bad after a curry...

I spotted in an old photography book instructions on etching a photo onto
glass. It involved coating the glass with a albumen and a sensitising
agent and at some point using bitumen powder, to act as a mask, the bitumen
adhering to the emulsion created with the albumen and sensitising agent.
All fine up to now (ok powerdered bitumen anyone). I decided not to bother
when it required the glass plate to be held over fuming hydroflouric acid.

--
http://www.petezilla.co.uk

On 21 Nov, 00:49, Paul Friday wrote:
In message ,
krishnananda writes

Hydrofluoric acid does damage glass.

And bones - never get it on your skin.
--
Paul Friday

It might be oxalic acid that the fungus is using. This is an organic
acid known to attack e-glass which is the glass used in glass fibre. E-
glass contains metal oxides to give it low electrical conductivity
properties (it also gives it increased strength) and optical glass
contains similar metal oxides, some of them the same. It will be a
very slow reaction, though. Not like watching hydrofluoric acid etch
glass.

In message
,
RolandRB writes
It might be oxalic acid that the fungus is using.

Then keep your lenses away from rhubarb leaves.
On the other hand, a strong tea made from said leaves is good for
removing rust stains. Just don't drink the stuff.
--
Paul Friday

On 22 Nov, 22:45, Paul Friday wrote:
In message
,
RolandRB writes

It might be oxalic acid that the fungus is using.

Then keep your lenses away from rhubarb leaves.
On the other hand, a strong tea made from said leaves is good for
removing rust stains. Just don't drink the stuff.
--
Paul Friday

Sage words from Paul. For those of you who store your lenses away
wrapped in rhubard leaves, think again!