This paper started with a brief review of the chemical and physical factors associated with the deterioration of paper. It then combined them with several assumptions approximations and definitions to obtain an isoperm–a quantitative graphical measure of relative permanence. Graphs were then used to describe and analyze a number of situations and systems. The aim of the paper is to provide a language or device that aids understanding and communication of preservation issues and assists in making preservation management decisions.

Studies to refine the isoperm method by measuring delta h values for larger numbers and types of paper are underway. More detailed information about the relationship of relative humidity to moisture content and deterioration rate is being gathered as is information on the effects of relative humidity and temperature cycling. The extension of the isoperm concept to other media such as magnetic tape, textiles, and film is being undertaken; as mentioned earlier, application to film already has been made by the Image Permanence Institute.

An earlier analysis of the effects of deacidification and paper strengthening upon paper permanence is also relevant. Deacidification, like environmental control, fundamentally produces life extension by reducing the rate of chemical deterioration. The analysis not only quantifies the consequences of deacidification but describes the powerful synergistic effects of combining different modes of reducing the deterioration rate, for example, a 3x reduction from environmental change combined with a 4x life extension from deacidification of acidic papers results in a 12x increase in permanence.

In a more speculative vein, it appears that preservation and preservation management may be entering a stage of development when quantitative analysis techniques and models can be used to help make preservation management decisions. We may be seeing the formation of a discipline or sub-discipline with the term Preservation Metrics–rather like Econometrics in economics. Isoperms may be one of the measures that will be found useful in preservation metrics.