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Preservation Metrics
Type of Decay:
Natural Aging

Metrics Used:
Time Weighted Preservation Index (TWPI)

Interpretation:
Higher the TWPI, the better
TWPI Value (years)
Interpretation
≥75
45-75
≤45

Measures:
The rate of "natural aging" as determined by the rate of spontaneous chemical change in organic materials.

  • TWPI integrates the T and RH values as they change over time into a single estimate of the cumulative effects of the envrionment on the rate of chemical decay.
  • TWPI is helpful as a quantitative comparison of the preservation quality of different storage locations or environments.


Applies to:
All Organic Materials (paper, textiles, plastics, dyes, leather, fur, etc)



Most Important for:
Sensitive or fast decaying organic materials (paper, books, film, and color photographs)

 

 

 

Educational Video

Watch the video below for examples and explanations of this type of decay.