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laid paper - The closely "lined" appearance in the finish of writing and printing papers created during manufacture by a dandy roll.
lamination - A process of reinforcing fragile paper, usually with thin, translucent or transparent plastic such as vinyl or polyester. Laminations are considered unacceptable as conservation methods because of potential damage from high heat and adhesives during application, instability of the lamination materials, or difficulty in removing the laminated item, especially long after the treatment was performed.
lantern slide (diapositive) - A mounted transparency on glass plate, that is placed in a still projector for the projection of an enlarged image on to a screen. Sizes vary by type standard 4 x 3 ½”, magic lantern slides 7 1/8 x 2 ¼” and 5 x 2”.
large format - Term describing photographic films, cameras, and techniques in the typical formats of 4"x5", 5"x7", and 8"xlO". The equipment and larger film offers controls that small and medium formats cannot, such as manipulation of the film and lens planes to achieve precise focus and perspective distortion corrections.
latent image - An image contained on film or paper prior to development. A negative exposed to light in a camera or a print exposed under a negative contains an invisible image referred to as a latent image. The image is made visible by chemical development.
layered mat - A double or triple mat, a mat made up of several pieces of matboard one on top of the other.
light stain - Discoloration on paper caused by overexposure to any light source, particularly light energy sources with heavy ultraviolet energy.
light-fast - Fade-resistant to light and especially the ultraviolet in sunlight. Usually refers to dyes or pigments used in coloring papers, fabrics and artist's materials.
light-sensitive - Materials which undergo changes when exposed to light. The commonly used photographic light-sensitive materials used in films and papers are the silver halides, diazo dyes, biochromated gelatin and the photoconductive materials used in Xerography. With most photographic materials, the changes are not apparent until the material is developed.
lignin - An acid organic substance found in wood pulp. It is removed in the chemical pulping process, but is not removed in the manufacture of low grade papers made of ground wood pulp, such as newsprint.
lignin-free - In paper, this term indicates there are only trace amounts of lignin (usually less than 1%). This is desirable because lignin in paper tends to decompose into corrosive and acidic elements.
linen tape - Water activated, adhesive backed, tight woven fabric tape commonly used as hinging tape for mats.
lithograph - A print made by a surface printing process dependent on the rejection of oil and water or some similar attraction-and-repulsion system. The classic type is the stone lithograph, in which the image is made on a smooth piece of limestone by drawing with a lithographic crayon or painting with tusche. The stone is then soaked with water and inked with an oil-based ink, which is attracted to the oily surface of the image but repelled by the wet stone. Paper is put in place and pressure is applied by running it through a press to transfer the ink to the paper.
litmus paper - A type of paper which has been chemically treated with dye extracted from lichens rendering it sensitive to pH. Blue litmus paper turns red in the presence of acid. Red litmus paper turns blue in the presence of alkali.
low resin basswood - (See basswood.) Basswood has lower resin content than most other commercially available woods.
low sulfur content - As the name implies. All papers exhibit some sulfur content, however certain processes in refining pulp can reduce the amount of sulfur present, providing the paper with extended life before breakdown.
low tack adhesive - Implies adhesive or items used with adhesive will be re-positionable. (e.g., Post- It Notes by 3M utilizes a low tack adhesive, as does drafting tape and positionable mounting adhesive.)
lux - A unit of illumination; the illumination on the surface of a sphere of radius one meter when a point source of one international candle is at the center of the sphere. 10.76 lux = I footcandle; I lux = 0.0929 footcandles.