Jamie,
The following is quoted from my Operator's Manual for our Preservation
Environment Monitors from the Image Permanence Institute at the Rochester
Institute of Technology;
"The Preservation Index is a means of expressing how ambient temperature and
RH affect the chemical decay rate of collections. PI has units of years and
gives a general idea of how long it would take for vulnerable organic
materials such as poor-quality paper to become noticeably deteriorated,
assuming that the temperature and RH did not change from the time of
measurement onward. PI helps us to quantify how good or bad the
environmental conditions are at that moment for chemical deterioration of
the collection. The "years of life" aspect of PI values was chosen
deliberately to reflect the behavior of relatively short-lived materials.
PI is not meant as a predictor of the useful life of any particular object.
It is simply a convenient measure of the effect of current environmental
conditions on the overall life expectancy of the collection, using
shorter-lived materials as a yardstick."
And the TWPI, then, is "... the total effect of changing conditions over
time ... The TWPI makes it possible to measure the effects, not of just one
set of conditions, but fluctuating conditions, over a whole period of time,
expressed as a single value."
So, when they say "noticeable deteriorated", I'm thinking that means the
typical darkening of the paper, less flexibility, etc. Not necessarily
totally destroyed, but enough deterioration that you can see that the paper
is starting to break down. And, typically, higher temperature and relative
humidity levels as well as fluctuating levels will speed up these chemical
reactions and shorten the life of paper artifacts.
That's just my understanding of it. I'd also love to hear from others as
well.
Sandy Hempe
Conservator
Missouri State Archives
-----Original Message-----
From: Nelson, Jamie [mailto:[log in to unmask]]
Sent: Tuesday, December 11, 2001 8:28 AM
To: [log in to unmask]
Subject: environmental controls - preservation index
I'm re-posting this in hopes that someone will respond. The original post
seems to have been lost amid all of the food chatter.
Colleagues -
I've been reading New Tools for Preservation: Assessing Long-Term
Environmental Effects on Library and Archives Collections by the Commission
on Preservation & Access (1995). I am a bit confused about the Preservation
Index and the Time-Weighted Preservation Index. I am in the process of
garnering institutional support to improve our environmental conditions and
I am looking to provide some information to convince the administration of
the need to have better control over our temp and RH.
This is where my confusion comes in. According the the PI chart, our
materials have an approximate predicted lifetime of 47 years, based on our
current temp and RH (67 and 50%). I would like to show that investing in a
better HVAC system and some building upgrades will allow us to change the
temp and RH and lengthen the predicted lifetime of the materials.
Basically, I'm looking for a justification for the expense (to justify it to
them - I don't need much convincing).
The question I've already been asked is: If the PI chart is right, how come
our collections (dating to 1860 and before) aren't dust already?
I'd appreciate it if someone could point out my faulty logic or better
explain the value of the PI and TWPI charts.
Much obliged for any assistance, and I will post a summary if there is
enough interest.
Jamie Nelson
Jamie Nelson
Special Collections Librarian
Augustana College
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