AIC’s 40th Annual Meeting, Joint Sessions: Objects + Reseach and Technical Studies, May 9, Some Unusual, Hidden, Surprising or Forgotten Sources of (Possible) Sulfur Contamination in Museums and Historic Buildings

Presenter: Paul Benson

Sulfur is well known as an agent of deterioration associated with atmospheric pollution, but sulfur was, and still is, intentionally introduced into buildings as part of the construction process, and is a part of some objects in museum collections. This presentation by Paul Benson was tremendously informative about how sulfur may be hiding in plain sight and damaging collections.  The talk provided examples of the use of sulfur past and present, and provided an example of effective control of sulfur used in the construction of an exhibition space.

Molten sulfur is an excellent electrical insulator. It has very good adhesive, handling, and casting properties that make it a good fill material. It goes through a flexible stage when cooling and it expands slightly (3%) on setting. In the US plaster ceilings were repaired with molten sulfur until the 1920s and buildings built before 1940 may have sulfur behind the surface of the walls as an insulator or fill material.   Conservators carrying out CAP surveys should be mindful of these possibilities.

There are unsuspected modern uses of sulfur as well. Used as an inexpensive filler in Chinese-manufactured dry wall imported to the US between 2001 and 2009, it caused extensive damage and reconstruction. Sulfur with additives is used instead of Portland cement in Canada because it has considerable shorter set time.

The Nelson-Atkins Museum discovered that the cause of severe mottling of bronze sculptures was sulfur applied behind the  numerous travertine sides of display cases integrated into the structure of the walls.  This situation was successful remediated by removing each piece of travertine, and applying  Marvelseal® with Beva®.

Sulfur has been used as a fill material in bombs. Police forensics use sulfur to take very accurate casts of footprints in snow.  These objects may be stored for long periods of time and contaminating other evidence.

Molten sulfur has been used since antiquity as an adhesive.  Pliny may have described its use as an adhesive for glass (depending on the translation). Sulfur was used as an adhesive in Rome, Greece, and Byzantium. All stones in the Thetford treasure at the British Museum were set with sulfur.  Sulfur was used to secure iron rods holding together elements of stone sculpture.

Sulfur can be found as an inlay material in furniture marquetry particularly in the sixty years from 1760 forward.  Sulfur will take on the appearance of mother of pearl with repeated heat treatments and can be found as “pearl” inlay on guns and  guitars.

Objects may be made of sulfur. “Spences Metal” is an iron-sulfur alloy used in the years around 1880. It can take a high polish and imitate a variety of metals. At the time hoped to be in inexpensive replace for bronze. “Ebonite” was made of rubber with 30-40% sulfur and was used to manufacture buttons and casters for furniture among other utilitarian objects that may be in museums of attached to objects in a collection.

Sulfur has been found in an historic clock cast around the weight to hold it in place. The “lead”  of German pencils made before 1770 is a combination of graphite mixed with sulfur. Coins may have been cast in sulfur lined plaster casts.  And among the seemingly innocent items that might be in a conservation lab sulfur is present in Plasticine® and pencil erasers.

This presentation provided a useful warning about possible contamination from sulfur present in unpredictable places and provided a wide range of examples to guide in hunting for an unseen source of corrosion.