Recently, I got to go on an unofficial friend tour of an art conservation lab in a museum. We met one of the conservationists who was repairing a shattered ancient Greek pottery vase. She pointed out an imperfection in the restoration work and said that it could never be like it was again because pottery is under tension, which is lost when it breaks, and that’s why broken pieces will never fit back together exactly.
My question is: why is this? Where does that tension come from? I assume it comes from the firing process, but I’d like to know how. And why does glass not do this? Or does it?
In: 32
Glass does it too.
And yes it’s the firing process, or more specifically the cooling down process afterwards.
When the material is hot it expands slightly. Then when it cools down it tries to shrink again, but during the cooldown the mobility of the atoms slowly reduces so they kinda get stuck in the expanded shape.
How much tension there is depends a lot on the materials being used and how fast the cooldown happens. If you cool them too fast they can simply shatter
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