Revision of ISO 18920 Imaging Materials – Reflection Prints – Storage Practices

The International Organization for Standardization (ISO) has recently published a revised version of their storage standard for reflection prints. The standard’s scope includes both traditionally printed photographic images as well as modern digitally printed images. It does not include recommendations for documents printed with digital output systems (see ISO 1799 Information and documentation -- Document storage requirements for archive and library materials). The original ISO 18920 standard was published in 2000. The previous recommendations for long-term storage of reflection prints lumped all digital processes into a single category, “All other”, and put the maximum allowable storage temperature for these materials at -3° C and the relative humidity range at 30-50% RH.

Table 1. New ISO 18920 Recommendations

Digital Print Process Maximum Temperature Humidity Range
Electrophotography 16° C 30-50% RH
Inkjet (dye and pigment) 2° C
5° C
30-50% RH
30-40% RH
Dye sublimation


2° C
5° C
30-50% RH
30-40% RH

The primary changes to the standard include allowing prints made with electrophotography to be stored nearer room temperature at 16° C rather than the previous sub-zero temperature of -3° C and raising the maximum temperature for all other digital print types (inkjet and dye sublimation) above the freezing point (see table 1). It is possible that this was done to prevent physical damage from freezing and thawing prints, though proof of such damage is not supplied.

“The rates of degradation and the potential for physical problems with extremely low temperature and/or low relative humidity storage is not well known for rapidly changing technologies such as thermal dye transfer (dye sublimation), thermal wax transfer, electrophotographic, and the many different ink jet image media (dye, pigment, wax) and base media (porous, swellable, plain paper).”

The standard also acknowledges that certain colorants (pigments) may be more robust over time in dark storage than others (dyes), but recommends that if print colorant cannot be positively identified that the most conservative, and therefore coldest, storage conditions should be used. IPI supports this position.

“Some current ink jet prints, especially those utilizing inks made from stable pigment or optimized dyes printed onto stable supports as recommended by the manufacturer may have very good image stability at temperatures warmer (up to 16 °C) than the recommended cold storage temperatures listed for extended-term storage. Where the identification of the type of ink and base cannot be determined … the colder temperatures listed shall be used”.

It is not clear from the standard what the new storage condition recommendations are based on. There are no references to published research on the subject. IPI is currently working on experimentation that will create data upon which the recommendations in this standard can be validated or ultimately revised. Pending that research, IPI recommends following the current standard. Where institutions may want to deviate from the standard is when the paper used to create a print is of questionable quality (e.g. contains groundwood or recycled content). Such prints may need cold storage.

The new standard can be purchased from the ISO website: