[Aavso-photometry] Re: Crud on filters

[Richard Miles]

Bill Goff wrote:

> I've begun to wonder if this is more of a preventative maintenance 
> problem; a few times a year cleaning the filter with alcohol or something 
> just to keep the crud from accumulating.
>

I tend to agree Bill.  Although the BG39 filter glass effloresces (that's 
the chemical term) in humid atmospheres, it does not seem to change the 
colour of the glass when inspected visually.

So like you say, keeping it polished may be a good strategy but watch what 
you use as the glass is quite soft - tin oxide is probably less hard than 
alumina or rouge.  A soft lint cloth may be the best option.

The white surface layer might be soluble in a very weak acid such as lemon 
juice - I'll give it a try and let you know.

Richard