This post is my longest to date, and I have put off publishing it for the past couple of weeks. I couldn't seem to find my voice and get across the information that I wanted to. I enjoy injecting my thoughts, viewpoints, passions, and recommendations into the posts I write. This post is more information and research rich, with less of the personalization that I like. However, this is vital information that I feel compelled to convey in the most straight-forward, fact-filled way.
I have had the opportunity since my last post to work with a number of historical sites, and I am continuing to learn about the absolute importance of maintaining the appropriate climate and environment so that preservation can be successful. History connects us on such a personal level to those who came before us. It gives us insight to why we are where we are today as an individual, a family, a country, and a people. Not to mention, these structures are built with an artistic attention to detail and a charismatic aura that simply does not find its way into our structures today. Do not get me wrong, the buildings that are being built today are the work of engineering genius and they are impressive in so many ways. However, In my opinion, they lack the character that I see in so many historical sites around cities like Richmond, Charleston (SC), Savannah...just to name a few. I want these places and artifacts to be around for generations to come so they too understand the journey that was taken.
The ominously labeled agents that I touched on above (agents of deterioration) are the factors that act negatively upon an object from the time it is created. the NPS says there are four agents related to the category "environment", which are as follows: temperature, relative humidity, light, and air pollution. I will touch on all with the exception of light, as I would be speaking without being educated on this---and I do not make a practice of speaking unintelligent. My goal is to help institutions understand what each one of these agents is, what contributes to the agents' license to kill (yea I went there), and how to eliminate the threat or at least reduce the effects.
Let's begin by laying the foundation of this discussion by going over the types of objects or materials that are housed within these buildings or sites and are vulnerable to these agents. Broadly speaking, there are three categories of materials that make up these historical gems: Organic, Inorganic, and Composite.
Organic objects are derived from plants or animals, and show themselves in wood, paper, textiles, leather, skins, horn, bone, and ivory, grasses, bark, lacquers, plastics, some pigments, shell, and biological natural history specimens. The NPS states these organic items share characteristics such as: containing an element carbon, are combustible, absorb water from and emit water to the surrounding air, are sensitive to light, and are a source of food for mold, insects, and vermin (gross!). These items are vulnerable to deterioration from extreme changes in temperature and humidity.
Inorganic objects still have a geological origins, and come in the form of metals, ceramics, glass, stone, minerals, and some pigments. These items have undergone extreme heat or pressure in their creation, are not combustible at normal temperatures, can react to their physical environment to change their chemical structure (ex. corrosion), may be porous, and are typically not sensitive to light.
Composite objects, are made up of two or more materials. For example, a book is composed of several materials such as paper, ink, leather, thread, and glue. Depending on the materials, these objects may have characteristics of both organic and inorganic objects while the individual materials react to the environment in different ways.
The actual deterioration of these objects and materials is the change in either the chemical makeup or the physical structure. This deterioration rears it's ugly face of destruction in the form of rusting, corrosion, fading, darkening, rotting, cracking, warping, shattering, structural failure, to name a few.
We touched on what the materials are and what can happen to them, now let's get into what these agents are: Temperature and Humidity. If you're like I was prior to having an understanding of HVAC (albeit still a limited understanding at present) you know when you're hot you turn the thermostat down and when you're cold, you turn it up. That was literally my understanding prior to getting into this business. There is a bit more to it than that so I have found out.....
Temperature and Humidity, these two forces work together to create a climate inside the conditioned space. We feel fluctuations physically in both, and so do the aforementioned objects. It is important to understand what the adverse affect of these fluctuations can be so that preventative action can be take to preserve most effectively.
Temperature is defined as a measure of motion of molecules in a material. When the temperature increases, the molecules move faster and spread out causing the material to expand. When temperature decreases, molecules....you got it....they slow down and the material contracts. At higher temperatures, chemical reactions and biological activity increase-neither of which is a good thing. These chemical reactions can cause extreme deterioration that can go unnoticed for quite a long time, at which point it may be too late to save the object. Biological activity sounds even less fun-creepy crawly critters chewing (say that 5 times fast). Insects eat more and breed faster in warmer temperatures.....*shivers*. Additionally, materials can soften at these higher temperatures. At lower temperatures paints, adhesives, and other polymers can fracture.
A good temperature range to shoot for is, on average, is somewhere between 64 and 68 degrees. Just as important as the actual temperature is maintaining a consistent temperature. Fluctuating temperatures can cause materials to expand and contract rapidly, setting up destructive stresses in the object. Temperature in turn has a hand in determining relative humidity-when temperature varies, relative humidity varies.
Relative humidity is defined as the relationship between the volume of air and the amount of water vapor it holds at a given temperature. Water plays a large role in various chemical and physical deterioration, making relative humidity an important factor in preservation efforts. Excess humidity in these facilities can come from many sources and show themselves in many forms. Exterior humidity levels, rain, bodies of water, wet ground, broken gutters, leaking pipes, moisture in walls, human respiration and perspiration, wet mopping, flooding, and cycles of condensation and evaporation.
As a benchmark for relative humidity, 50% RH means that the air being measured has 50% of the total amount of water vapor it could hold at a specific temperature. It is important for me to note and for you to understand that the temperature of the air determines how much moisture the air can hold. Warmer air can hold more water vapor, because an increase in the temperature causes the air molecules to spread out-creating more space for more water. Relative humidity is directly related to is also inversely related to temperature. In a closed system, when temperature goes up-RH goes down. When temperature goes down-RH goes up.
Since the materials that are housed in or make up these facilities have already endured the elements for many many years, they need just the right environment to survive. Relative humidity that does not fall within the needed range can cause deterioration in numerous ways. When RH is too high chemical reactions increase, just as they do when temperature rises. Metal corrodes, dyes fade, wood swells and warps, adhesives become softer, paper may buckle, canvas paper can slack, and biological activity is supported by higher RH levels. Low RH levels can cause shrinkage, warping and cracking of wood, leather can crack and flake as can photographic. Finally, an environment where RH significantly varies has a large effect on organic materials. Swelling and contracting by constantly adjusting to the environment creates deterioration. These deterioration may come suddenly or may happen over time, and potentially go undetected until a final layer gives way or structural damage occurs. Materials that are at the high risk to fluctuations are laminate and composite materials such as photographs, veneered furniture, and paintings.
The RH range needed for a specific collection is based on what the collection includes. I have included ranges for a number of different materials and objects below. Again, this is an average and actual ranges are on a case by case basis.
Archaeological Materials
Negligible Climate-Sensitive Materials:.................................................................................30%-65%
Climate Sensitive-Materials:..................................................................................................30%-55%
Significantly Climate Sensitive Materials:.............................................................................30%-40%
Metals:....................................................................................................................................<35%
Natural History Materials
Biological Specimens:.............................................................................................................40%-60%
Bone and Teeth:.......................................................................................................................45%-60%
Paleontological Specimens:.....................................................................................................45%-55%
Pyrite Specimens:....................................................................................................................<30%
Paintings:...............................................................................................................................40%-60%
Paper:.....................................................................................................................................45%-55%
Photographs/Film/Negatives:...............................................................................................30%-40%
Other Organics (wood, leather, textiles, ivory):.................................................................45%-60%
Metals:....................................................................................................................................<35%
Ceramics/Glass/Stone:..........................................................................................................40%-60%
Many collections include a vast array of the above materials and objects. With that being said, a good RH to shoot for in a museum setting would be around 45% relative humidity.
We've all heard the phrase: "A picture is worth a thousand words". To conclude this post, I am going to use some visual examples of deterioration to hopefully allow all of these facts and figures to come full circle and make sense. Two thousand words from me to you....
This was a lot of information, and I hope that I laid it out in a way that was easy to follow and comprehend. I have found a passion in preserving history, one that I wasn't aware of until I was immersed in it. The beauty and the story of history is one that I cannot describe with words on a blog. It is something that has to be experienced, has to be taken in, has to be absorbed into the mind, body and soul. With knowledge, we can ensure that these buildings and collections are around for generations to come and give them the gift of history.
-Luke
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