If you have historical thermal copies from the 1950s and 1960s amongst your archival records or you are producing or receiving thermal copies for archiving, a number of points need to be considered to minimise risk of image loss.
For records of permanent or long-term value
Current evidence indicates that all thermal papers are fairly unstable and cannot be considered permanent. This is especially true for the more modern papers which, even with optimum storage and handling conditions, can be expected to display significant fading in as little as five years. Papers from the 1950s and 1960s are not as unstable as this but can still be considered to be of limited permanence.
Thermal paper is, therefore, not a suitable medium for records of permanent or long-term value. To avoid loss of data in such records, photocopies of thermal paper documents should be made on permanent or archival copy paper. These photocopies should be retained as the archival copies. After the photocopies have been checked for completeness and legibility, thermal paper copies may be destroyed as a normal administrative practice.
If, for whatever reason, an original thermal paper needs to be retained, a copy should be made as a back-up, in case the original becomes illegible. The paper should then be stored in environmental conditions, i.e. not exceeding 20 °C or 50 per cent relative humidity. Extremes of temperature and humidity can cause rapid deterioration of the image. Avoid prolonged exposure to light as this can also speed up the deterioration of the image. To avoid the possible danger of thermal copies affecting other papers stored adjacent, thermal copies should be filed separately from other paper records.
For records of short-term value
Because the prospective life span of a modern thermal paper image is so short, the use of modern thermal papers is even a concern in relation to records which have only a short-term value. Therefore, if a thermal copy is required to last any longer than five years, or if it will be handled a lot, consideration should still be given to producing a copy for retention and reference. If this is not possible, the papers will require particular care if they are to last. This should include storing them away from extremes of temperature and humidity, avoiding prolonged exposure to light and storing them separately from other documents.