Slow glass is a speculative material that appears to capture and hold light within its subatomic particles. This is caused by the high refractive index of the material. The refractive index is a measurement that describes how quickly light travels within a material - a process that is visually denoted by the bending of light or sound as it passes through different mediums.

The high refractive index is due to its dense crystalline structure. This structure is unlike the amorphous atomic pattern of glass which is somewhere in between a liquid and a solid.

To look through - or within - slow glass is to see an out-of-step present:

‘This is a special kind of glass that light takes eleven seconds to pass through, so the image was still visible in it eleven seconds after my hand had been removed’. (1)

Light and images that are held within slow glass are released according to the material's thickness. In this example, slow glass is eleven seconds thick. The image held within the glass disappears when light finishes its eleven second journey through the material's subatomic particles. The glass continues this process - absorbing and releasing light.

Slow glass illuminates the temporal fabric of the world. Time is dislocated and the linear borders that we impose upon it are permeated.

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1. Bob Shaw, Other Days, Other Eyes, (London: Pan Science Fiction, 1972),p.21