Re: filmscanners: cleaning neg's, sharpening

[Arthur Entlich <artistic@ampsc.com>]

Mark Thomas wrote:

> Just a couple of quick comments..
> 
> 1. Cleaning neg's with water
> Bear in mind that if you use anything but 'unexposed' distilled water as 
> a cleaning agent, you are in fact using carbonic acid..!
> I used to work in a oceanographic lab, and while checking the pH levels 
> of a distilled water producer, I was surprised to discover how acidic 
> the 'pure' water was.  The resident chemist gently explained that H20, 
> when exposed to air, absorbs CO2 and degrades quite quickly to a 
> carbonic acid solution, of about pH 5.0-5.5 I think. (I'm flying by 
> memory here - any chemists on the list feel free to correct..)
> 
> Keep that in mind if considering water for cleaning fragile items!!
> 

Well, I think he was giving you a bit of a jest.  As you probably know, 
water is supposed to be neutral, or pH 7.  Drinking water, at least here 
in Canada, cannot be beyond pH 6.5 (it can go alkaline to 8.5). 
Although it is true that water does absorb minimal amounts of CO2, the 
pH is not likely to vary much, and the amount of acidity is minimal. 
However, if you live in an area with severe acid rains, it could get as 
acidic as a tomato, but this is due to the rain going through sulfur 
dioxide and becoming sulfuric acid when the rain goes through it.  If 
your water to begin with is fairly neutral, the amount of CO2 absorption 
to standing water will not do much... if it did, most fish could not 
survive in it.  Soda pop is created by bubbling CO2 through cold water 
and it has to be kept under pressure in order to keep it there.

Art