sentences:  For instance, temperature may be slightly lower in winter to save energy costs, but the change should be effected slowly, so as not to place the fibers under undue stress.As for humidity, the preservationist or conservator should aim for a relative humidity of 50%, though, as with temperature, some small fluctuation is allowable, as long as it occurs gradually (Mailand).In enclosed display or storage cases, humidity can be somewhat maintained through the use of silica gel crystals.