Ammonium Chloride Misting

The last stage before permanent storage of the tablets is final photography. This is usually, though not necessarily, done prior to final publication when scholars working on the tablets want to examine the tablets under the best possible conditions.

The first step in final photography is coating the tablets with a fine layer of ammonium chloride. This gives the surface of the tablet a stark white appearance that highlights the wedges of the cuneiform script and any seal impressions.

Granules of ammonium chloride are placed in a specially shaped glass tube designed by David I. Owen. The tube, on a stand, is held horizontally over a low flame. The back end of the glass tube is attached to a length of rubber surgical tubing, the other end is open. After the ammonimum chloride is heated and vaporized, air is blown through the tube and the ammonium chloride mist coats the surface of the tablet. It is vital that the surface of the tablet has a uniform, white coating in order to maximize the contrast between the surface and the writing and impressions. Care must be taken to coat only the parts of the tablet that will be photographed immediately because the ammonium chloride dissipates from the surface fairly quickly. This also reduces the chance of leaving distracting finger prints in the ammonium chloride. After photographs are completed the ammonium chloride can be removed by simple brushing or by allowing it to evaporate.