1. Collection Care:
Environmental Factors
Part I: Temperature and Humidity
Valinda S. Carroll

2. Agents of Deterioration
 High
Temperature
 Humidity
 Light
 Pests and Fungi
 Handling
 Air Pollution

3. Environmental Monitoring
Determine current conditions for storage
and exhibition, before investing in
conservation treatment.
It would be a poor investment to conserve
an artifact, only to return it to a damaging
exhibit gallery or storage space. A
monitoring program allows an institution to
set preservation priorities according the
specific needs of its collection.

4. Temperature and Humidity
Traditionally, museum climate control
has been based on human comfort, the
capacity of the heating and air
conditioning system, and the limitations
of the building.

5. Temperature and Humidity
Since 1994, published research has measured
damage induced by climate fluctuations. In
some instances, this research has resulted in
wider “acceptable” climate ranges, adjusted
for local conditions.
Collections housed in historic buildings may
be required to tolerate slight seasonal climate
fluctuations in order to preserve the buildings.

6. High Temperature
High temperatures may  Causes cross-linking
damage artifacts in (makes materials become
several ways brittle)
 Causes chain scission
(makes materials weaker)
 Makes materials expand
(causes splitting and
delamination)
 Lowers relative humidity
(causes shrinkage and
splitting)

7. Temperature and Humidity
Relative humidity is directly affected by temperature,
so the two factors should be monitored together. An
increase in temperature results in a decrease in
relative humidity, because warm air has the capacity
to hold more water. As the temperature is reduced,
relative humidity increases until it reaches 100%,
and water condenses on surfaces. This temperature
is called the “dew point.” Dehumidification is
important to avoid condensation. A relative humidity
range of 35% to 55% is safe for most types of
collections, and allows moderate temperature
variations.

8. High Humidity
Excessive humidity is  Accelerates chemical
damaging to art and damage
historic artifacts  Promotes swelling,
distortions, and
delamination
 Encourages mold growth
 Increases insect activity
(especially combined with
high temperature)
Warped floor tiles

9. Measurement Tools
 Handheld  Recording
Thermohygrometer Hygrothermograph
 Thermometer and  Electronic Data loggers
Psychrometer  Temperature and
Humidity Indicator
Cards

10. Handheld
Thermohygrometer
Advantages
•Displays relative humidity
•Displays temperature
•Portable
•Easy to use
•Does not require additional
equipment or supplies
•Inexpensive

11. Handheld
Thermohygrometer
Disadvantages
•Does not record over
time
•Does not store readings
•May be inaccurate, and
difficult to calibrate
•User must purchase
batteries

12. Aspirating Psychrometer
•Compares wet bulb
and dry bulb
temperature to find
dew point and relative
humidity
•Contains light to
make thermometers
easier to read

13. Aspirating Psychrometer
 Uses a fan to evaporate
moisture from cloth on wet
bulb
 Can assist in calibrating
Wet bulb other instruments
 More reliable and easier to
use than sling
psychrometer

14. Aspirating Psychrometer
• Does not record over
time
• Requires slide rule or
mathematical
calculations
• Does not generate
documentation

15. Temperature and humidity guidelines
from the psychrometer manual:
The temperature range of 70-80F degrees for
libraries and museums on this chart is aimed at
human comfort rather than collection care.

16. Recording Hygrothermograph

17. Recording hygrothermograph
Advantages
•Shows temperature
Red
temperature
line

18. Recording hygrothermograph
Advantages
•Shows temperature
•Shows humidity
Blue humidity
line

19. Recording hygrothermograph
Advantages
•Shows temperature
•Shows humidity
•Records over time: daily, monthly, or
weekly
•User may calibrate to improve accuracy
•Some types run without batteries or Toggle switch for 1 day,
electricity (wind-up clockwork 7 days, or 32 days
mechanism)
•Easy to use
•Paper chart provides long-term record
for comparison over seasons or years
•Continues to work during staff vacations
or even during disasters

20. Recording hygrothermograph
Disadvantages
•May require regular winding or battery
replacement
•User must purchase paper charts and
replacement pens
•Expensive
•Paper charts require storage space
•Red and blue ink lines may be faint and difficult
to see
•Cannot shift between Fahrenheit and Celsius,
nor show dew point, etc.
•Cannot be included in computer-generated
reports and presentations

21. Data logger
Advantages:  Records over time
 Small enough to fit into
exhibit case or packing
crate
 Data can be loaded into
standard spreadsheet
software to generate
reports
 May be less expensive
than hygrothermograph

22. Data logger
Disadvantages
 Requires batteries
 Inexpensive models
cannot be read without
computer
 Inexpensive models
must be downloaded
individually, by hand

23. Humidity Card
Advantages
• Small enough to fit into frame,
exhibit case, or shipping crate
•Inexpensive unit cost
•Does not require batteries
•Does not require computer or
slide rule

24. Humidity Card
Disadvantages
• Imprecise
•Not durable
•Does not record over time
•Cobalt blue salt is toxic (orange
humidity cards are non-toxic)

25. Temperature Card
Advantages
•Inexpensive
•Easy to use
•Portable
•Small enough to fit into frame,
exhibit case, or shipping crate

26. Temperature Card
Disadvantages
•Imprecise
•Does not record over time
•Does not generate permanent
documentation
•Not durable

27. End of Section
Please proceed to Part II: Light