1 INTRODUCTION

THE TESTING OF MATERIALS and the interpretation of research are fundamental issues in paper conservation. This paper presents the properties of paper as a material and shows how paper variables relate to paper testing and the interpretation of research.

Although paper degradation and its mechanisms and products are not fully understood, it is generally recognized that the chemical reactions of hydrolysis, oxidation, and cross-linking are involved. Physical properties associated with degradation are loss of strength, embrittlement, and loss of bonding within the paper matrix, among others. There are several options for testing either the chemical or physical properties of paper. Chemical testing methods provide information on the molecular level, while physical tests describe the total overall structure. Paper conservators are presented with explanations of chemical degradation processes, and should question why they are often measured using physical rather than chemical methods.

Paper is a composite material: physical tests provide information about the integrated paper network rather than isolated contributing components. This is important because in addition to the chemical composition of the sheet, paper properties are dependent on the network matrix, the bonding within that matrix, and the fibers' properties responsible for the bonding. These categories are interrelated and within each, variables exist that affect the paper structure as a whole.

The composite nature of paper limits the usefulness of testing isolated components, either chemical or physical. It is difficult to relate a single component back to the overall structure. The usefulness of chemical testing may be limited by lack of correlation to the overall physical structure of paper. Likewise, physical tests cannot provide information on a chemical reaction, or predict permanence. For example, loss of strength (a physical measurement) in a sheet of paper cannot be interpreted as resulting from the removal of cations (a chemical reaction) by wash water. The results of a particular test, chemical or physical, may be interpreted in a number of ways, and making the proper interpretations and conclusions depends upon the total research design and expertise of the researcher.

Paper scientists use the combination of tests that fit their project design and that provide the necessary data to answer their specific inquiry. It is important to realize that standards established by TAPPI (Technical Association of the Pulp and Paper Industry) or ASTM (American Standards and Testing Methods) are guidelines developed to provide consistency and accountability within the paper industry, and were not developed specifically for research. Although the procedures discussed in the standards provide useful information, the methods themselves are not definitive. The data require interpretation within the framework of probable reactions and the test methods used for the evaluation.