[Aavso-photometry] Re: Crud on filters

[Shawn Dvorak]

Bill Goff wrote:

> Shawn,
> Interesting.  Are yours mounted and if so, did you unmount them for 
> this cleanup?
>
> Bill
>
> On Oct 15, 2005, at 3:34 PM, Shawn Dvorak wrote:
>
>>>
>>> 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
>>>
>>>
>> I cleaned the relatively mild crud off of my V filter today using 
>> cerium oxide using my finger and moderate pressure.  A few minutes' 
>> polishing completely removed the crud and left the filter looking as 
>> good as new.  I'll hopefully get to try it out this evening if the 
>> clouds don't continue to thicken.
>>
>> Shawn
>>
>
>

Bill,

My filter is from Schuler, and is cemented into the cell so I didn't 
have a choice.  The cerium oxide cleaned up nicely with warm water.  The 
crud was not very bad, and primarily near the center of the filter so it 
was easier to get at.

I've had a couple nights' photometry with the filter and it seems fine, 
though I haven't checked the transformation coefficients yet.  The flat 
I made certainly looks a whole lot better after polishing.

Shawn