Polyurethane (PU) 3

Spectroscopy chart PU

High heeled shoe, 1980s

Polyurethane

Source

Leamington Spa Art Gallery & Museum

History

The condition of the sole and heel is consistent with having been worn.

Material

The upper, heel and sole is made of the featured material, polyurethane with a metal core and some metal decoration.

Degradation

The sole is made from a foamed polyurethane, which is very sensitive to the atmosphere due to its high surface area. The oxygen in the air has caused oxidation which has made the material brittle. This has caused deep cracks in the sole leading it to fall apart. Plasticiser in the form of a white powder (suberic acid) has migrated from the bulk of the sole.

 

Degradation typical of the material not visible in this example

Discolouration.

Treatments

The white powder could be removed by gently brushing with a soft brush and museum vacuum. When doing this, wear a dust mask. The shoe would need to be supported underneath while this takes place.

There are experimental treatments available for degraded foams but their success depends on the fragility of the object. Consult PUR Facts, Conservation of Polyurethane Foam in art and Design, Thea van Oosten, Amsterdam University Press, 2011.

Display and storage

A support of soft tissue should be provided. They should be stored in the dark in an environment of low humidity (20 - 30% RH).

In order to prevent further degradation by oxidation, the object may be stored in an oxygen-free environment. However, this increases significantly the space required for storage. The system also needs to be monitored and changed periodically.

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