GLOSSARY

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L

lamination

A process of reinforcing fragile sheet material, usually using transparent or translucent sheets of plastic or paper. Hot and cold lamination are possible. The materials used may be archival, but the technique is not an approved conservation practice. It should never be used for valuable items because it can be virtually impossible to remove without damaging the item.

leather

The skin of animals prepared for use by tanning or a similar process. See also Alum tawed leather; Parchment and vellum; Tanning.

leather dressings

Oil-based mixtures applied to tanned leather to help maintain flexibility and water resistance. Most dressings contain an oil, commonly Neatsfoot oil. Leather dressings can not prevent chemical decay, protect against acidic pollutants, or restore leather which has become decayed because of chemical influences. They should be used sparingly and carefully on museum objects, as their use can leave the leather sticky and darker in colour.

leaf, leaves

A single sheet of paper, parchment or vellum, each side of which forms a page of a book. The plural form is leaves.

light

Electromagnetic radiation with wavelengths capable of causing the sensation of vision. Visible light is within the wavelength range of 400-700nm nanometres(nm), or 4 x 10-7 metres to 7.7 x 10-7 metres. Variations in the wavelength produce different sensations in the eye, corresponding to different colours. See also Visible spectrum.

lignin

A complex organic material that, together with cellulose, forms the woody cell walls of plants. Lignin surrounds the cellulose fibres and provides the stiffness and strength which enables trees to stand upright. It is chemically stable in wood, but becomes unstable when the wood is broken down to make paper. Lignin is susceptible to photochemical deterioration and, as it breaks down, produces acids which are extremely harmful to paper. Therefore, the preparation of pure cellulose by removing the lignin is an important step in the manufacture of pulp for the paper and rayon industries.

loadings (in paper)

See Filler.

low oxygen fumigation

A method of disinfestation by exposing materials to an atmosphere deficient in oxygen. See also Oxygen scavenger.

lumen

The measurement unit for the quantity-as opposed to the intensity-of light given out by a light source. The lumen measurement remains constant for a light source and does not alter if the readings are taken at a greater distance from the light source. Measurements of light intensity, which vary according to distance from the light source, are known as lux. See also Lux; Microwatts/lumen.

lux

The measurement unit used to record the intensity to which a surface is lit, or the brightness of the light. Lux varies according to the distance from the light source. Lux can be measured by a lux meter and is calculated in terms of one lumen per square metre. See also Illuminance; Kilolux hour; Lumen.