Cleaning Marble with Ammonium Citrate

Ammonium citrate solutions were tested to determine possible damage on marble using two concentrations, four different values of pH and several variations in application. As pH dropped from values of 10 to 7, marble chips immersed in the solutions showed increasing dissolution of calcite, and polished marble tiles to which solutions had been applied showed increasing loss of gloss and brightness.The least damage to marble tiles was produced when solutions were covered during application, and single cleanings were found to be less damaging than multiple cleanings of the same total application time. Comparison with other cleaning agents — ammonium thioglycolate and ethylenediaminetetraacetic acid (EDTA) — showed that ammonium citrate solutions could be as mild as thioglycolate when used in some conditions, such as high pH and low concentration. In contrast, ammonium citrate solutions could harm the stone significantly when used in other conditions, such as pH 7 or high airflow. In these cases, the damage was nearly as much as a 2% solution of EDTA al pH 10. This study emphasizes the need to develop new cleaning products, research which can only go hand in hand with a better understanding of the various interactions taking place between cleaning agent, substrate and environment.

Source  /  Claire Gervais, Carol A. Grissom, Nicole Little and Melvin J. Wachowiak Studies in Conservation