Sustainable Preservation Practices for Managing Storage Environments Series # 3. Basic Elements of the Environment & Their Effect on Decay

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1 Sustainable Preservation Practices for Managing Storage Environments Series # 3 Basic Elements of the Environment & Their Effect on Decay

2 Environmental Basics Temperature Relative Humidity Dew Point A basic understanding is necessary to defining and achieving an optimal environment. theconservator.wordpress.com

3 Environmental Basics Temperature, Relative Humidity, and Dew Point are interrelated

4 Environmental Basics Temperature levels, in combination with Relative Humidity levels, govern the rate of chemical decay Relative Humidity plays a significant role in mechanical and biological damage Dew Point temperature determines the Temperature and RH combination you can achieve

5 Temperature A measure of heat energy expressed in degrees Fahrenheit (F) or Celsius (C) Easy to measure (thermometer) Relatively easy to control

6 High Temperatures Sustained high temperatures Increase the rate of chemical reactions Determine how fast organic materials will decay Magnetic media, plastics, film, dyes, leather, rubber, and acidic paper are vulnerable In damp conditions high temperatures can lead to increased biological activity Insects eat more and breed faster Mold will grow faster in certain temperature ranges

7 Low Temperatures Cool temperatures (below 54F/12C) slow the rate of chemical decay Lowering the temperature can improve preservation quality IF you maintain a moderate RH (30 to 50%) Cold temperatures (below 40F/4C) are beneficial for film and photographic collections Cold temperatures can increase brittleness in rubber, plastics, or polymers found in modern paints and coatings

8 Very Low Temperatures Freezing Conditions (at or below 32F/0C) are fine for many objects and freezing is a good method for pest control Very low temperatures can cause desiccation in vulnerable materials causing fractures in paints, adhesives, and other polymers Vulnerable materials include magnetic tape and acrylic paintings

9 Temperature Fluctuation Wide and frequent fluctuations in temperature may cause fractures and delamination in vulnerable objects. Furniture, paintings, ivory, and composite objects are particularly vulnerable Managing high and low temperature extremes is more important than maintenance of steady temperatures year round.

10 Relative Humidity Represents how saturated the air is with water vapor Determines the amount of water contained within collection materials Harder to understand Difficult to Control Control is energy-intensive

11 High RH - Dampness High RH (over 65%) can result in mechanical damage Objects absorb and release moisture in response to the surrounding environment As more water is absorbed chemical reactions involving water happen faster Between 20% and 50% RH, reaction rates TRIPLE Mold risk and insect activity increase in damp conditions

12 Low RH - Dryness Low RH (below 25%) can result in physical damage as organic materials react to moisture loss Signs of damage include shrinkage, warping, cracking, embrittlement, and delamination

13 RH Fluctuations Prolonged periods of high and low RH are more significant than short term fluctuations Wide and sustained RH fluctuations increase the rate of mechanical decay Dual threat: Brittleness, warping due to low moisture content Metal corrosion, swelling, dye bleed due to high moisture content

14 Dew Point Dew Point is a measure of the absolute amount of water in the air Without humidifying or dehumidifying, indoor and outdoor dew points are usually the same

15 Dew Point As air heats up, it can hold more water Red line shows the saturation point

16 Condensation occurs when the temperature at which air containing a specific amount of water becomes saturated Dew Point

17 Why Dew Point Matters At a constant Temperature: RH and DP increase or decrease together At a constant RH: T and DP increase or decrease together At a constant DP: as T increases, RH decreases as T decreases, RH increases

18 Deterioration Basics Decay occurs through three main pathways Chemical Decay or Natural Aging Mechanical (Physical) Damage Biological Processes

19 How Chemical Decay Works Organic materials tend to degrade spontaneously which is why chemical decay is sometimes called natural aging Both temperature & relative humidity play a role in chemical decay.

20 How Chemical Decay Works Chemical reactions Objects react with air, moisture, contaminants Some reactions are slow, others quite rapid The reaction rate is depends on the levels of both heat and moisture

21 How Chemical Decay Works Every T & RH combination defines a rate of chemical decay The rate slows down when conditions move toward cooler and/or drier It is possible to determine the overall rate of chemical decay by integrating (weighting) warm, humid periods and colder, drier periods over a span of time

22 How Chemical Decay Works Organic materials are vulnerable Paper, wood, leather, vellum, plastics, dyes, varnishes, textiles, ethnographic material Also some inorganics Metal corrosion Calcareous material

23 Evidence of Chemical Decay Deterioration of pigments, fading, discoloration Embrittlement of papers & textiles Deformation shrinking, sagging, melting

24 How Mechanical Decay Works Water vapor forces its way into and out of moisture-absorbing materials until a balance between interior and exterior moisture levels is established (equilibration) Hygroscopic materials absorb and release water depending on the RH of the surrounding air

25 How Mechanical Decay Works When RH is low, water-absorbing objects contract and become brittle Below 20% RH danger increases rapidly When RH is high, these objects expand and become soft and flexible Above 65% RH danger increases rapidly

26 How Mechanical Decay Works Composite objects are particularly vulnerable Various materials respond differently, causing stress between various components of the object

27 How Mechanical Decay Works When to Worry Very DRY Conditions RH below 25% RH for weeks Very DAMP Conditions above 65% for weeks Repeated excursions between extremes Seasonal extremes

28 Evidence of Mechanical Decay Response to dryness Buckling, cracking, tearing, delamination, flaking Response to dampness Softening, melting, warping Response to repeated changes in moisture breakage, cracking, surface loss, deformation

29 How Biological Decay Works Biological decay is caused by living organisms, most notably mold, mildew and insects Life processes are biochemical in nature and depend on proper temperature and moisture conditions to thrive

30 How Biological Decay Works Temperature helps determine the likelihood and severity of biological attack, but the major environmental factor is moisture Both molds and insects thrive at moderate temperatures and elevated RH

31 How Biological Decay Works Mold spores are always present in the atmosphere and just require a sustained high RH for a certain period of time to propagate Organic materials are particularly vulnerable Active mold produces enzymes that can digest cellulosic materials such as paper, leather and textiles

32 How Biological Decay Works In general, maintaining RH levels below 65% eliminates the risk of mold growth Insect infestations are minimized by keeping RH below 50% and temperatures cool IMPORTANT POINT when you lower the storage temperature, the RH rises Too often attempts to improve conditions by cooling the space result in issues with biological decay Use the Dew Point Calculator to define safe levels

33 How Metal Corrosion Works Corrosion is a form of chemical decay found most commonly in metal objects and objects with metal components Examples include silver tarnishing, rust damage, bronze corrosion

34 How Metal Corrosion Works Corrosion is primarily the result of moisture in the air and begins at RH levels of about 55% or greater The presence of pollution, dust, salts, oils or active corrosion can allow it to occur at lower RH levels

35 When to Worry Focus on environmental extremes and collection vulnerabilities Sustained periods of dampness, dryness and heat matter most Find out the capabilities of your mechanical system to lower the dew point (dehumidify) or raise the dew point (humidify) Identify the most vulnerable materials in your collection

36 IPI Preservation Metrics Designed to identify preservation risks and benefits of the storage environment Algorithms developed by IPI over the last 20 years that convert collected T & RH data into comparative values for analysis of preservation quality

37 IPI Preservation Metrics Each metric evaluates the quality of environments over a period of time into a single value representing the degree of risk (or benefit) for a particular form of material decay, taking into account all the ups and downs of T & RH during the monitoring period

38 Quick Look at one year of temperature and RH data and tell me what the risk to collection materials is:

39 OR use the Preservation Metric calculations which provide you with an immediate overview you can use to evaluate spaces:

40 Compare Locations Where When Risks/Benefits for each Chemical decay type of Decay Mechanical decay Risk of mold

41 Advantages of Preservation Metrics Quick, standardized overview Point out the risk of each mode of decay in a given space You have to decide if they are important to the collection materials in that space Flag potential problems Show change over time Make convincing case for improvements

42 Analysis with Preservation Metrics Computational analysis of raw data allows for: Quantitative measurement Comparison of storage locations Removes subjectivity from simple analysis of graphs

43 Chemical Decay Metrics Preservation Index (PI) and Time-Weighted Preservation Index (TWPI) Based on combined influence of temperature and RH on spontaneous reactions in organic materials Integrate the effect of good and bad environments over time One calendar year yields best overall rate estimate

44 Chemical Decay Metrics TWPI 75 or higher TWPI between GOOD conditions indicates a slow rate of chemical decay in organic materials OK conditions fine for most materials but may not be good for fast-decaying organics TWPI 45 or lower RISK potential indicates an accelerated risk of chemical decay, especially for fast-decaying organics The higher the TWPI, the longer it will take for a given amount of decay to occur

45 Mechanical Decay Metrics % Dimensional Change (%DC) Minimum/Maximum Equilibration Moisture Content (%EMC Min / Max) Based on moisture-absorption and dimensional change in an imaginary block of wood Warns of excessive dryness, dampness and dangerous excursions between extremes

46 Mechanical Decay Metrics Min EMC 5% AND Max EMC 12.5% AND %DC 0.5% Min EMC 5% AND Max EMC 12.5% AND 0.5% %DC 1.5% Min EMC 5% OR Max EMC 12.5% OR %DC 1.5% GOOD minimal risk of physical damage; not too dry or too damp, and almost no fluctuation between the two OK not too dry or too damp and minimal fluctuation between the two, however sensitive material may be at higher risk RISK heightened risk of physical damage; either too dry, too damp, or two much fluctuation between the two

47 Biological Decay Metric Mold Risk Factor (MRF) Based on combined influence of T & RH on germination rates of common mold species Integrates over time Warning system - Indicates likelihood and severity of mold outbreaks

48 Biological Decay Metric MRF 0.5 MRF 0.5 GOOD little or no risk of mold growth RISK indicates that mold spores have germinated, entering a vegetative mold state visible mold could be actively growing There is no OK rating for mold growth either there is the potential for germination (RISK) or there isn t (GOOD).

49 Metal Corrosion Metric Maximum Equilibrium Moisture Content (EMC Max) Based on the maximum amount of moisture in the environment, which promotes corrosion in vulnerable materials Warns of the risk of environmentallyinduced corrosion

50 Metal Corrosion Metric Max EMC 7.0 GOOD conditions indicates a minimal risk of corrosion 7.1 Max EMC 10.5 OK conditions fine for most materials but may not be good for material vulnerable to corrosion Max EMC 10.5 RISK potential indicates an accelerated risk of corrosion, particularly for vulnerable materials

51 What the Metrics are NOT Predictors of when specific objects or collections will become ruined Predictors of how long specific objects or collections will last

52 What the Metrics ARE Tools, based on decades of research, to help you understand, manage, and improve the storage environment for your collections IPI s Preservation Metrics are available in the eclimatenotebook online data management system