Fire

Fire produces a very extreme form of another agent - incorrect temperature. It also produces flames and smoke, but needs a source of fuel to keep going. Most organic materials make good fuel. Fire can cause irreparable damage to all types of objects by changing their structure - the exact effect depends on the material. For example:

paper, textiles and other organic matter can be reduced to ashes very quickly
many plastics will melt
wood, ivory and bone can be turned to carbon. Less intense heat will cause the material to become brittle, splintered and delaminated (the layers separate)
ceramics and stone will crack or shatter
if the fire is hot enough even tough metals can melt or crack

'Charity' by John Henry Foley (1861) shows smoke pollution, fire damage and calcination of the marble due to exposure to heat and water

(This piece is featured with the permission of Tameside Museums and Galleries Service, Tameside MBC. The conservation was grant aided by North West Museums, Libraries and Archive Council and the Friends of Tameside Museum and Galleries Service.)

Sometimes the damage is not obvious - high temperatures change the microstructure of a metal object. This may destroy valuable information on the way the object was made.

This early 20th century travelling trunk was damaged by smoke in a house fire, and had to be cleaned once acquired by the museum. Water from fire hoses and sprinklers can also cause severe damage.

Fire is not just a problem for the conservator - it can also be used to help identify materials. For example, the way a fibre burns tells us what sort of fibre it is - vegetal (eg cotton), protein (eg wool) or synthetic (eg nylon).

Burnt ivory is used in ivory black; a pigment made by grinding burnt ivory with oil.

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Damaged trunk
A 19th century travelling trunk damaged by smoke in a house fire