High humidity should be avoided for all photograph types to prevent blocking, ferrotyping and mold growth. However, inkjet dyes can also bleed severely when exposed to high humidity causing noticeable image blurring and color fringing (See Figure 1). As part of the ongoing DP3 Project, IPI performed a set of experiments to determine the absolute temperature, humidity, and time limits to prevent damage.
This research focused on a variety of dye printers and papers known from our previous work to be particularly sensitive to this type of damage. Nine different dye printer/paper combinations were evaluated along with one pigment printer/paper combination known not to bleed to serve as a control. Specimens were treated to twelve different time, temperature, and humidity combinations covering a time span from one day to four weeks, temperatures from 15°C to 35°C, and relative humidities (RH) from 60% to 90%. The tests included measuring CIELab color values with a spectrophotometer for a color patch target and line width changes with image analysis software for a CMYK line target. Figure 2 below shows untreated and treated lines. Note that the magenta dye bleeds the most, even in a black line.
It was found that relative humidity, temperature, and time all influence the extent of bleed and must be collectively considered. Figure 3 shows the time to bleed for the most susceptible inkjet print at 25°C (77°F). All conditions to the right of the gray area should be avoided. Prints should always be safe below 65% RH. Above 65% RH, bleed can begin in several weeks with time to bleed rapidly diminishing as humidity increases. Prints at 80% RH or higher can show noticeable bleed in less than 24 hours.