Contributors: Sophie Carman
pH is the measure of hydrogen ions (H+) in an aqueous solution. A solution can be categorized as acidic or basic based on the pH.
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The categorization of the pH of a material is based off of a logarithmic pH scale, which labels a material with a pH between 0 and 14 (Museum of Fine Arts Boston). A pH of 7 is considered to be neutral and is exemplified by pure water. Any solution with a pH less than 7 is categorized as acidic, such as hydrochloric acid or citric acid (Getty: Acidity). As the pH approaches zero, the acidity greatly increases. On the other hand, a pH greater than 7 is categorized as basic or alkaline, such as sodium hydroxide (Getty: Alkalinity). As the pH approaches 14, the acidity greatly increases. Electronic devices and simple pH strips are methods of testing the pH of a solution.
The stability and preservation of a material can be dependent on the pH of the depositional environment (Cronyn 1990). Generally, areas of high rainfall and low evaporation create acidic environments, whereas semi-arid areas are more prone to be basic environments. In order to promote preservation, the depositional environment of an object should be consistent with that of the environment during its use. Any change in environmental pH can lead to numerous degradation processes of an object, including hydrolysis, crystallization, or corrosion.
References[edit | edit source]
“Acidity.” Getty. Accessed April 1st, 2014. http://www.getty.edu/vow/AATServlet?english=N&find=acidity&logic=AND&page=1¬e=
“Alkalinity.” Getty. Accessed April 1st, 2014. http://www.getty.edu/vow/AATServlet?english=N&find=alkalinity&logic=AND&page=1¬e=
Cronyn, J. M. 1990. The Elements of Archaeological Conservation. London: Routledge.
“pH.” Museum of Fine Arts Boston. Accessed April 1st, 2014. http://cameo.mfa.org/wiki/PH