Re: Lens problem - fungus??

On 16 Nov, 04:29, krishnananda <mahaman...@[EMAIL PROTECTED]
> 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