The nonacid paper is a paper which has a pH neutral or basic (7 or slightly superior). This Propriété allows a conservation of the documents for long periods.

The paper worked out starting from the Pulpe of wood whose Lignine was not withdrawn yellows and worsens with time. When they are exposed to the light and/or heat, the Molécule S of the paper of wood pulp (acid) dissociate more quickly. It was only in years 1930 that the effects of the paper of wood pulp became known, when William Barrow (a bookseller) published a report on the deterioration of acid paper in the libraries. By fear of seeing the supports written to disaggregate little by little, measures were taken to improve quality of paper.

During the development, nonacid paper is treated with a weak base (generally Bicarbonate of calcium or magnesium) to neutralize the acids naturally present in the wood pulp, and it is plugged to prevent the formation of additional acids which could be formed starting from the application of a Durcisseur.

The bicarbonate is added in excess, to provide to paper a reserve Alcaline to provide a protection against the later attacks of the remaining acids in paper or is provided by the surrounding medium (atmospheric Sulfur dioxide). Paper intended to last for long periods (approximately 500 years) should contain approximately 3% ponderal carbonate.

Today, the majority of paper produce commercially is nonacid, but this is due to the passage of the Kaolin to the Craie like principal product of contribution in pulp: the chalk reacts with the acids, and thus makes pulp neutral or basic. The additives hardening contained in pulp and/or applied to the surface of paper must also be not-acid.

There exist various standards for not-acid papers. Sometimes paper having a pH between 6 and 7 is regarded as nonacid. The paper (alkaline) nonacid which is nonlying and in conformity with the standards of folding and tearing is authorized by the American National Standards Institute to carry this note: " The paper used in this publication is in conformity with the requirements of the American National Standards Institute for Information Science-Permanence off Paper for Printed Library Materials, ANSI Z39.48-1992."

The objective of the Norme S Z39.48-1992NISO ANSI is to establish the criteria for the art paper and nonlying to last several années" under optimal conditions in the libraries in the files. The anticipated result of the standard is to reduce the future problems involved in the Conservation.

The range of the standard is to cover the publications and the documents bought and maintained by the libraries and the files. Such work includes/understands academic newspapers, periodicals, significant Monographie S and official documents, work, imaginary or not imaginary.

The sign of paper certified ANSI is the ringed symbol of the Infini.