In 2013 the Bata Shoe Museum (BSM) organized an exhibition called Out of the Box: The Rise of Sneaker Culture discussing the evolution of sneakers from sports footwear to fashion accessory. In examining the shoes before they went on display we noticed they were showing signs of active deterioration. Inherent vice is a term used in conservation to describe a form of deterioration that is an inevitable aging process in a material component of an artefact. Many plastics, sometimes referred to as modern materials, deteriorate because of the chemical components of the materials that are used in the manufacturing of sneakers. How these shoes are worn and the environment in which they are stored also contribute to deterioration. Within the BSM collection historic sneakers were acquired with pre existing issues, while some of the newer sneakers in the collection are starting to show signs of early decline. Here are a few examples of what that means and looks like.

A pair of PF Flyers, acquired by the BSM in 2013, made between 1945 – 1959, are composed of rubber soles and cotton uppers. The sulphur used in manufacturing rubber off-gasses, meaning it emits volatile compounds, which can damage materials to which it is attached and also affect neighbouring artefacts in storage or within a showcase if the shoes are on exhibition. This is visible in the discolouration of the cotton which has turned from white to a browny-yellow colour. Aging has also made the rubber brittle, the soles are completely inflexible, the foxing (the band around the perimeter of the sole) is cracked, chipped and detaching from the cotton; the toecap has the same problems. The rubber coated eyestays around the grommets are cracked. This is the section of the sneaker through which the laces are threaded. The laces are made of cotton braid with cellulose acetate (CA) tags. The CA was originally clear, now it has yellowed and cracked.

The Puma RS Computer shoe was collected in 1995 the year the BSM opened. It was made in 1986 and is composed of many modern materials, the most problematic being the polyurethane (PU) midsole which has developed several interesting features. The foam is cracked, sticky, crumbling and has a white crystalline bloom on its surface. The foam is so soft that the indentation of a fingerprint from the previous owner is visible on one of the sneakers! The midsole has detached from the shoe except at the point where the toe end of the sole is glued to the toe end of the upper. The cotton twill tape band, shown in the photograph, holds the two components together so that when the sneaker is handled the sole/midsole does not yaw from the toe creating significant stress on the only point of attachment. These sneakers are so fragile that they were not included when Out of the Box traveled to other institutions.

The PONY M-100 was manufactured in 1989 and this pair was a gift to the museum from PONY for Out of the Box. They feature PU midsoles and PU heel cushions imbedded in the outsole. Both are exhibiting the same kind of deterioration. Both structural elements are cracked, a crystalline bloom is forming on their surfaces and the foam is flaking into little bits, some of which you can see stuck to the white surface of the ankle area above.

The 1993 Insta Pump Fury was gifted to the BSM by Reebok in 1995 complete with its original shoe box and CO2 cartridge. It is made of many modern materials, the ones of greatest concern are the polyvinyl chloride (PVC) tab at the back and the ethylene-vinyl acetate (EVA) midsole. The PVC tab is sewn between the yellow panels on the sides of the sneaker. There are two issues at play here: the panels are pulling outwards, the stitches have created perforations in the PVC that act like a tear line you would find on a mail-in order form. Essentially, the PVC tab has been literally torn apart by this combination of forces. One of the tabs completely disintegrated, the other was salvaged. While the EVA foam is stable it has been affected by the attached rubber outsole. In the picture you can see the surface colour of the EVA is transitioning from white to yellow. This pair was also deemed too fragile to be in the traveling exhibition.

The Nike Air Zoom Flight 95, named after the year it was manufactured, was also a donation to the BSM and featured in Out of the Box as a ‘must-have’ classic for sneaker collectors. The clear coating over the carbon fibre substrate on the sides of the shoe is made from PU. It is starting to exhibit deterioration with which you have become familiar while reading this blog: it has developed a foggy, white bloom on its surface.

The study of modern materials is a fascinating part of conservation. Its landscape is ever changing as museums and art galleries, aided by conservation scientists, strive to discover the best possible way to store and exhibit these important artefacts of our material culture.