Today we’re talking about temperature… or more so incorrect temperature because there’s always a temperature, but if the temperature is too hot or too cold, that’s where we can get in to some trouble with our museum and archaeological collections.
Let’s get in to it. Incorrect temperature can mean one of three things:
The temperature is too high
The temperature is too low
The temperature fluctuates too much or too quickly
Different types of materials react to various temperatures in different ways so you need to look at your collection to really see what the best mode of attack is for tackling this issue.
Temperatures that are too high can cause chemical, physical or biological damage to materials, and the hotter the temperature, the faster the rate of decay. So if we know that, we can figure out that a lower temperature therefore means a lower rate of decay. Materials that are very sensitive to higher heat are acidic paper like newsprint or mass market paperbacks, old films will also shrink in heat, materials based on cellulose and early plastics can also yellow and become very brittle which causes cracking. Some acrylic paints and canvas supports are very susceptible to higher temperatures.
A really scary thing that can happen if the temperature is too high, is that canvas oil paintings that are lined with a wax resin can actually detach from the lining. Of course it’s not an instant thing, but still a scary process. Glues can also soften under high temperatures, be they glues used in original manufacture or glues used during conservation treatments. Paraloid B72 for example has a glass transition temperature of 36 degrees Celsius. This is the point when it can start to soften and become weaker.
Materials that aren’t so susceptible to higher temperatures would be oil paint, regular paper, cotton and wood. That being said, they still degrade over time and lower temperatures do help in prolonging its rate of decay.
Now when I mean higher temperatures, I’m not talking 100s of degrees Celsius. Even a temperature as high as 30 degrees can drastically reduce the lifetime of an object. But the good news is, if you reduce the temperature by 5 degrees, you can essentially double the lifespan of an object. So if a sensitive object has a lifetime of 7 years in a room of 30 degrees, if you lower the temperature to 25 degrees, it can now be preserved for 14 years! This is some serious preservation magic right here. If we do some very basic math, that means if you store the same object at 0 degrees, it will survive for 600 years!
Of course you can’t keep it at 0 degrees forever because cold storage can be quite expensive, and using all that energy is also not so great for the environment, but you can see how museums and other institutions can use temperature to their benefit in order to prolong the lifespan of their materials. You might find museums can be a bit chilly, but never too uncomfortable and this is exactly why. They try and strike a balance between visitor comfort and object safety.
Now it seems like the lower the temperature, the better are right? Well... sort of. If the temperature is too low for certain materials, a lot of physical stresses can form. So that means they can become harder, more brittle and could be easier to crack.
Paintings can become more vulnerable to physical forces, the first agent of deterioration we talked about. Metal can crack and materials like leather and rubber that are supposed to be more flexible will become brittle.
So extremes are bad. We know this. The final kind of temperature we need to be careful of is fluctuating temperature. We know from science class back in elementary school that heat expands and cold contracts. So imagine if the temperature in a room is always fluctuation, getting hotter and colder multiple times throughout the day. That’s a lot of expansion and contraction, which can lead to a lot of stress being put on an object.
If temperature fluctuations happen too quickly, the object isn’t able to respond evenly and adjust to its new environment, and can cause physical stress, creating cracking or unstable materials. This one isn’t super dramatic as a lot of materials can handle some temperature change, but it’s in everyone’s best interest to keep temperature stable.
The biggest thing with fluctuation in temperature is the coinciding fluctuation in relative humidity. We’re going to be talking about relative humidity in the next video, but it’s the moisture in the air. Some materials are very susceptible to moisture, so this fluctuation is bad news bears for them.
So now we know what the risks are with each type of incorrect temperature, let’s get in to how we can control this and protect our objects as best we can.
Some best practices in regards to temperature control are to keep artefacts out of direct sunlight, where you can get warmer patches, make sure you’re installing a reliable heating system in your museum or storage space, use insulation to avoid dramatic fluctuations from outside and always monitor your temperature to make sure it’s stable. Stability is the most important factor. Even if your temp is a few degrees too hot or too cold, if it’s consistent and stable then you have a lot more other things that you can occupy your day worrying about.
It’s also a good idea to really look at the materials your objects are made out of and try to store them accordingly. If you have a cold storage room, take advantage of it for your most vulnerable objects.
Looking to find out more?
Canadian Conservation Institute- Agents of Deterioration: Incorrect Temperature by Stefan Michalski