The Unflowing Mist

On the inner side of the glass display case, a layer of mist came up.

Mist made of water vapor condenses into droplets on glass, slides down, and collects along the lower edge into a thin line of water. This layer does not. It hangs where it is, even, quiet, about two centimeters off the surface of the sarcophagus, as if there were another kind of air inside the glass.

The specification of the case is on record: double-glazed, nitrogen-filled interspace, independent dehumidification on the outer layer. The inner side should not fog at all; and if the dehumidification failed, mist would show up first in the corner with the largest temperature differential, not lie in one sheet against the face nearest the head of the exhibit.

Photographed with the wrist terminal, it does not come out. Switch to RAW, take another frame, magnify 200%, and the image holds clean glass and the surviving polychromy on the surface of the sarcophagus. The naked eye sees it, sees where its edge falls, sees which pane of glass it is pressed against.

A palm laid against the outside of the case: the glass is warm, as warm as the other three sides of the hall. The stretch behind the mist is no colder and no hotter. From another angle its upper edge is a straight line, level as if ruled, following neither the curve of the glass nor the direction of the airflow inside the case.

In museum records a thing like this usually ends up in one of three places. Engineering assigns it to the HVAC ducting: the night-time plant changeover, a shift in zonal pressure differential, condensate going where it should not. Conservation assigns it to the exhibit itself: moisture content moving in a wooden object, water vapor coming off the gesso layer. The people who have actually stood the night shifts have a third account, which they keep out of the reports and mention at handover in one line—that pane is not clean tonight, do not get too close.

Anyone who has been in the trade long enough knows that when an object starts doing things that do not work physically, the problem usually does not lie in its condition. Temperature and humidity logs can be checked, a case can be taken apart, a dehumidifier can be swapped out; nothing that can be swapped out is ever the reason for mist like this.

At 22:04 the mist was gone. The inner side of the glass was clean, with not a drop of water left on it and not one track where anything had slid down.