Poultice Desalination Using Buffered Rigid Gel with Ion Exchange Resin

Jessica Abel, Brittany Dinneen, and Renee A. Stein


This paper presents an innovative method to remove soluble salts from extremely fragile materials, using a buffered agarose gel mixed with an ion exchange resin. Many highly unstable objects that are actively crumbling and/or spalling cannot withstand desalination by repeated immersion in water baths. Alternative poultice treatments can be slower, more difficult to monitor, and less effective at removing soluble salts. Historically, objects too fragile to undergo desalination have been stored in climate-controlled enclosures, which can be difficult to maintain and often prevent examination or display.  Conservators at the Carlos Museum of Emory University were faced with the challenge of stabilizing a 4-inch tall slip-decorated, ceramic vessel (4600-3600 BC) and a 4-foot tall limestone funerary stela from the Egyptian New Kingdom (1292-1191 BC). As the earliest example of Levantine decorated pottery in the Near East collection and one of the few large, relatively intact reliefs in the Egyptian collection, these objects were slated for display in the permanent galleries. Both objects exhibited salt efflorescence, along with crumbling and spalling surfaces; neither was stable enough to undergo desalination by immersion. Microchemical tests, X-ray diffraction, X-ray fluorescence, and thin-section analysis determined the presence of chlorides, nitrates, sulfates, and phosphates confirming that the extreme deterioration exhibited by these objects was the result of salt movement within the low-fired ceramic and marly limestone.  Experiments to extract soluble salts were conducted with a wet poultice comprised of buffered agarose gel mixed with an ion exchange resin. Preliminary testing on mock-up ceramic and stone tiles aided materials selection and method development. This testing will be discussed along with the two case studies. Challenges encountered and overcome during these treatments included mixing large batches of gel, covering expansive and complex surfaces, maintaining a wet system, preventing mold growth, and monitoring desalination progress. Observations and practical solutions will be presented, offering lessons that can be utilized in the future investigation and application of this method. Ultimately, soluble salts were reduced, increasing the stability and resilience of these highly fragile objects, thus allowing them to be made accessible for public appreciation through display.

2020 | Online | Volume 27