In general, RH equilibrium occurs slowly for the entire mass of an object. Therefore, seasonal changes have the greatest effect. However, the surfaces may feel daily changes, causing stress within the structure. Moisture Equilibrium Curves have been charted for many materials showing how rapidly the object's moisture content equilibrates with the relative humidity. Few museum objects respond significantly to fluctuations under an hour in duration.
Many objects take days, weeks or even months to respond.
Daily or diurnal RH cycles are important for objects with short equilibration times, such as thin or absorbent materials. For example, on movie film hanging on a clothesline, gelatin equilibrates in minutes while the thin plastic equilibrates in hours. This difference could cause the gelatin to separate from the plastic substrate when RH fluctuates. For each collection material, the time scale of RH equilibration is important. Placing the object in a cabinet, drawer or box can slow equilibration lessening the likelihood of mechanical decay.