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[filmscanners] Re: What can you advise

This is what I so enjoy about the internet:

I sitting in my home at the computer and "listening in" on a discussion
between a Mycologist and an Architect specializing in moisture control,
about relative humidity where terms such as "from the mold's point of
view"  are used.

On a filmscanner list, no less!

It's fascinating stuff, in a sort of "who would have thunk" sort of way,
and I mean this with sincerity, without sarcasm, humor or malice.

Now, which one of you wants to take on why it seems moisture only wants
to come into my house and never seems to want to leave it ;-) (that one
WAS stated with humor, BTW)

Actually, I am going to ask Bob for some mycology help, but I'll do that
off line (and no, its not about how to get psilocybe
cyanescens/baeocystis/semilanceata/stuntzii/pelliculosa/cubensis etc. to


Bob Frost wrote:

> Henning,
> Having just read my reply to you, I think I can simplify the matter further
> still for any photographers who are still with us.
> You said:
>>Actually, Bob, 100% relative humidity at 5 C is equal to about 29%
>>relative humidity at 25 C.
> Fine; it is in the sense that each probably holds equal WEIGHTS of water (I
> don't have the precise figures to hand).
> But from a mold's point of view, 100% RH at 5 degrees is perhaps a trifle
> cold, but the air is saturated, condensation will occur, and the mold will
> grow all over your film, given time.
> However, at 25 degrees and 29% humidity, despite the equal amount of water
> in the air, the air can hold many times that amount of water before it
> becomes saturated, and no mold will grow on your film because any water will
> evaporate and the mold spores will not germinate or will become dessicated
> if they land on your film.
> You might think, that is clear from the RH values - 100% and 29% - it is
> obvious that 29% has less water than 100%. But my other example shows this
> is not always true - 80% RH at 25 degrees is equal to 30% at 5 degrees FROM
> THE MOLDS POINT OF VIEW. The only way of directly comparing the dryness of
> the air from a mold's point of view is to measure the amount that it is
> below the maximum water-holding capacity of the air. While Relative Humidity
> allows comparisons to be made at any one temperature, you must measure
> Vapour Pressure Deficit to compare dryness between one temperature and
> another.
> I hope that is clearer.
> Bob Frost.
> ----- Original Message -----
> From: "Henning Wulff" <henningw@archiphoto.com>
>>>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,
>>30% relative humidity at 5 C is about 9% relative humidity at 25 C.
>>I'm an architect (and architectural photographer) with special
>>qualifications relating to moisture control in buildings, and the
>>various aspects of moisture as applicable to construction and
>>building science - no specialized knowledge of mycology, other than
>>how it relates to buildings :-).

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