The summers in Chicago are hot and humid, while the winters are dry and cold. This variation in humidity is particularly damaging to materials such as fiber and wood which easily absorb and then give off moisture. Repeated cycles of expansion and contraction due to the absorbion of moisture and subsequent drying weakens the structure of the artifact.

The cycle is even destructive to stone because it causes salt crystals to form, breaking up the artifact and eventually turning sandstone to sand, and limestone to chips of lime. The fluctuations affect metal objects by encouraging the growth of damaging corrosion layers.

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