[filmscanners] Re: What can you advise?

["Bob Frost" <bob@frost.name>]

Art,

As a former mycologist, I too was rather suprised when you said molds could
grow at anything over 30% humidity. I once studied the effect of humidity on
the growth of a mold for my PhD, and found that unless the mold was growing
on a substrate containing plenty of water, it couldn't grow out into air of
less than 95% humidity at normal room temperature.

The problem is that last word - temperature. As an example, 80% relative
humidity at 25 degrees C is equal to 30% at 5 degrees C, so a mold that
needed 80% humidity at 25 degrees would be able to grow at anything above
30% humidity at 5 degrees. This is because the measurement of humidity that
is normally used, relative humidity, is fine for comparing humidities at
constant temp, but when you change the temp, the water-holding capacity of
the air changes dramatically, and other measures such as 'saturation
deficit' are needed to properly compare the ability of the air plus moisture
to support growth at different temperatures.

Plus of course, the biggest danger is condensation. If the temperature drops
below the ability of the air to hold the moisture, the excess will condense
out (dew at night, fogging of lenses when you bring a cold camera or pair of
spectacles into a warm room). A cold outside wall to a room may suffer
condensation and mold growth for the same reason, even though the general
humidity of the room would not support growth.

Bob Frost.



----- Original Message -----
From: "Arthur Entlich" <artistic-1@shaw.ca>
To: <bob@frost.name>
Sent: Monday, September 30, 2002 12:28 AM
Subject: [filmscanners] Re: What can you advise?


As both you and Henning suggested, based upon review of my files, my
suggestion of mold growth at over 30% humidity was too conservative.

After doing a scan of my physical paper files, I found my memory had
failed me, as a reference by Kodak regarding preventing fungal growth on
films indicated humidity levels should be kept under 50%, not 30%, as I
had indicated. (Kodak Pamphlet AE-22) Prevention and Removal of Fungus
on Prints and Films

I then did a Google search, and several sources suggested anything under
60% was probably safe.

So, it would appear your 45% humidity level is safe under most
circumstances.

Kodak and other sources did suggest fungicidal agents can be used during
the processing to further lessen risks.

Art

Austin Franklin wrote:

>>>I'm curious if you have any references on that.  I've not had any mold
>>>growth, and it seems quite comfortable...and as I said, no
>>>
>>camera, equipment
>>
>>>etc. problems at all.  It's been a most palatable environment.  The
>>>dehumidifier is off during winter, probably from October to April.
>>>
>>
>>Not off hand.  It probably depends upon temperature and general mold
>>conditions.  We live in a very mold prone environment here.  I think
>>Kodak had some studies which I read many years ago about suggested
>>storage for film and they made some mention about optimum humidity
>>levels.  I might have it here somewhere...
>>
>
> Hi Arthur,
>
> I would greatly appreciate the link or reference.
>
> Regards,
>
> Austin
>
> P.S. Would you please be so kind as to pass the crumpets? ;-)
>


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