The Regional Review

Volume IV - No. 1

January, 1940


test tubes
Note: Openings of the spout should be slightly larger than the diameter of a No. 2 pencil lead.

Many Service technicians who have attempted to photograph small objects, such as fossils or artifacts, in which form and sculpture may be more important than differences in color, have encountered difficulties in obtaining satisfactory lighting. Objects having high relief show excessive contrasts; flatter objects lose much of their fine detail and be come toneless gray outlines. Many of these difficulties may be overcome by coating the object to be photographed with a film of sublimate of ammonium chloride. If applied thinly and uniformly such a coating lights up all sculpture so that fine details can be photographed with great accuracy.1

A simple apparatus for producing and applying the sublimate is shown at the left. When the operator blows into the mouthpiece, M, the fumes of hydrochloric acid (HCl) and ammonium hydroxide (NH4OH) unite at the outlets, O, and form clouds of white sublimate of ammonium chloride. When the object to be photographed is held close to the outlets the sublimate is deposited on it. Depending on the thickness applied, the coating varies in color from a light blue to an ivory white. Details of form are brought out faultlessly and can be examined microscopically without exhibiting crystalline structure.

The reagents should be concentrated. They should not be placed in the apparatus until it is ready for use, because if they are allowed to stand in the bottles moisture accumulates and prevents successful operation. If small quantities are used the bottles can be emptied and dried frequently. The apparatus does not work well in wet weather. Before the sublimate is applied, all traces of grease or oil should be removed from the object with dilute grain alcohol applied with a soft brush. A thin bluish or ivory coating of sublimate gives better results than does a dense white layer. Above all, the film should not be blown on too vigorously for this destroys the desired smoothness. After being photographed, the sublimate can be made to disappear if the breath be blown on the coated object; but it is perhaps better to remove it by brushing liberally again with alcohol. The writer has used the whitening process in photographing thousands of fossils and feels confident that others may profitably give it a trial. --- H. S. Ladd.

(1) Many geologists use this process and the necessary apparatus has been described in print at least twice, but the descriptions are in technical publications that are not available everywhere. Much of the data in the present account is taken from a report by R. S. Bassler, "The Bryozoa, or Moss Animals," Smithsonian Report for 1920 (Publication 2633), pp. 339-380, 1922.

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Date: 04-Jul-2002