ACID-FREE PAPER
In principle, paper that does not contain any free acid. Special precautions are taken during manufacture to eliminate any active acid that might be present in the furnish.

ADDITIVE
A mineral, chemical or dye added to pulp and coatings to give it special qualities such as opacity.

AIR DRIED PAPER
Paper dried by exposure to air, generally warm.

AIR-DRY PULP
Technically, pulp of which the moisture content is in equilibrium with the ambient atmosphere. Commercially, pulp at a theoretical moisture content agreed between the buyer and the seller (e.g., 10 per cent is common).

AIR-KNIFE COATED PAPER
Paper coated by a process where the freshly applied wet coating is smoothed and the excess removed by means of a jet of air discharged from a slit orifice placed at an angle to the web.

AIRMAIL PAPER
Paper made in the lightest substance consistent with strength and a good surface, for reasons of postage costs. Generally produced in white, off-white or pale blue for stationery purposes, usually below 40g/m2. Manifolds and lightweight bonds are also often known as airmail papers.

ALUM
A term commonly, but incorrectly, applied in the paper industry to various qualities of aluminum sulphate.

ANTIQUE
A characteristic low degree of surface finish that typifies certain commercial descriptions of paper such as Antique Wove, Antique Laid, etc.

ANTI-RUST PAPER
Paper containing added substances that give it the property of protecting the surfaces of ferrous metals against rusting.

ANTI-SET-OFF SPRAY
A device used on the delivery end of the printing machine to prevent set-off by projecting a fine spray of liquid or powder at the sheet.

AOX
Adsorbable Organic Halogens. AOX expresses the amount of organic chlorine compounds in effluent produced as the chlorine chemicals react with the residual lignin in the bleaching of pulp. A safe AOX limit is easier to achieve using chlorine dioxide than with chlorine.

APPARENT DENSITY
The quotient of the grammage of a paper and its thickness in micrometers.

ART PAPER
This is a generic term given to woodfree coated papers, which has traditionally referred to papers in the upper quality bracket and which have a high polished surface. Today the term is less common because of the introduction of more categories in the sector. However, "Real Art" is still used for those woodfree coated papers, gloss or matte, which are considered to be of the very highest quality.

ASH CONTENT
The amount of residue when a sample of paper is burned under controlled conditions so that all ignitable matter is removed. The ash derives from the mineral loading in the paper.