Preservation Environment Calculator
Use this tool to explore the relationship between temperature, relative humidity, and dew point, and assess the quality of your collection environment.
Set your conditions and the results update as you go. Note: this tool assumes steady conditions and are a guide only. It is not a substitute for monitoring or a conservator’s judgment.
Your conditions
Air temperature in the space.
Moisture in the air, as a share of the most it can hold at this temperature.
Under these conditions, any object in the space at or below 9.3 °C will collect condensation.
Results
Natural aging
Years to noticeable chemical decay if the room held these conditions constantly, from IPI's Preservation Index. The index is benchmarked on acetate film and used as an indicator for organic materials that decay by hydrolysis. Higher is better.
Mold risk
Uses the same days-to-mold model as Conserv Cloud, held at constant conditions. Warm, damp air lets mold germinate sooner; the model treats germination as unlikely below 65% RH or outside 2–45 °C. Microclimates within a space can differ from the readings you enter.
Mechanical damage
Organic materials shrink and embrittle when very dry and swell when very damp. Equilibrium moisture content (%EMC) below 5% or above 12.5% is rated at risk of cracking, warping or flaking.
Metal corrosion
Uses equilibrium moisture content (%EMC) as a proxy for the moisture available at metal surfaces. Rated Good below 7% EMC, OK from 7 to 10.5%, and Risk above 10.5%.
How this works
Dew point
Dew point is the temperature at which the water vapour in the air would start to condense. It is calculated from temperature and relative humidity using the Magnus approximation (a = 17.625, b = 243.04). At a constant dew point, warming the air lowers RH and cooling it raises RH, which is why managing dew point is central to managing decay risk.
Natural aging
Natural aging is measured by the Preservation Index (PI), as defined by the Image Permanence Institute. It is based on the Arrhenius model for the chemical decay of organic materials, calibrated on cellulose acetate, and is expressed as years to noticeable decay. The reading assumes the room holds these exact conditions constantly. A time-weighted PI (TWPI) averages this rate across real, fluctuating readings over a logging period, and is what a monitored space should be judged on. We recommend using the PI and TWPI as a general indicator of environment quality, not as a precise prediction of decay.
Mold risk
Mold risk uses the same model as Conserv Cloud, based on data published by the Image Permanence Institute. This tool assumes steady conditions; in practice, variations in temperature and relative humidity influence actual mold risk. For a more nuanced calculation, upload your logger data to Conserv Cloud. Note also that this model assumes that mold cannot germinate below 65% RH or outside 2–45 °C, and real germination also depends on the surface and on how long conditions actually persist.
Mechanical damage
Hygroscopic materials such as wood, paper, leather, textiles and paint layers take up and release moisture to stay in equilibrium with the air. Their equilibrium moisture content (%EMC) is estimated here with the Hailwood–Horrobin sorption model using Simpson's coefficients. This is a static-condition check; the dimensional-change (%DC) metric in Conserv Cloud uses the swing in EMC over time instead.
Metal corrosion
Metal corrosion risk uses the same %EMC value as a proxy for the moisture available at metal surfaces.
The Good / OK / Risk ratings follow IPI's Guide to Sustainable Preservation Practices.
Run this analysis on your own logger data, over time, with a free Conserv Cloud account.