Improving the Methodology to Conduct Aqueous Extract pH Measurements
Authors: Suwaileh Wafa Ali , Korenberg Capucine , Wang Quanyu 
Published: July 2019

Museums artifacts are susceptible to deteriorate inside showcases due to environmental parameters that are often uncontrollable. Museum showcases are made of different materials that may emit corrosive gases which can be harmful to the museum's collection. Packing materials if they are not inert can also cause damage to artifacts especially if they indirect contact with organic objects. Therefore, it is very important to carry out the pH test in preventive conservation to determine the stability of these materials used in showcases, packaging and storage, and the treatment of artifacts. The British Museum used to employ distilled water but replaced it with the Elga Pureable Unit filled with a pureable flex unit. Because of the low conductivity of this type of water it is difficult to obtain pH values in the range of 6.5–7.2. The purpose of this research is to investigate a suitable methodology to measure aqueous extract pH using two different pH meters. This issue is associated with the water quality used and it is of great concern. Therefore to resolve these problems, the ionic strength of purified water should be increased but the concentration to be used for the extraction needs to be determined. Experiments were carried out over a 60-day period utilizing a HI 2210 bench meter and a H138 minilab meter. A variety of materials which are going to be used in showcases such as white paper, tissue, fabric, cardboards, medium density fiberboard (MDF), silk and cotton fabric and washed sand were examined. Materials used for packing and storage such as, archival boxboard and white papers were also tested. To investigate a suitable extraction time, de-ionized water was boiled for different periods of time to remove carbon dioxide from water. A variable concentration of potassium chloride was added to increase the hydrogen-ion concentration of de-ionized water and purified water. These additions of potassium chloride also lead to a reduction in the acidity of water which was influenced by carbon dioxide absorption from the atmosphere. The pH readings which were obtained by using the above methods were unsteady. Hence, the successful proposed method was to use purified water with the addition of 2 drops of KCl solution (14.5 grams of solid KCl dissolved in 100 ml de-ionized) then measure the pH using the minilab meter. Three readings were taken every 10 minutes. The result showed a stable pH value of 6.7. Accordingly, this proposed method was repeated to test the stability of fabric, tissue and medium density fiberboard. It was concluded that, the solution of these tested materials reached equilibrium after one hour and 15 minutes of extraction as the measurements were stabilized. The pH value of pure water with a resistivity value of 18.2 MΩ and the addition of 2 drops of KCl was close to neutral. The minilab meter is more convenient due to its sensitive electrode that measures the pH of low ionic strength of water and provides more accurate results. Also this meter allowed the use of smaller quantities of water by adding a drop on the electrode as well as being less time consuming. The successful methodology can be used as an indicator to select suitable commercial materials for museum collections. This research will provide the conservators and museum professionals with a method to prevent damage to the artifacts caused by emission from the materials used in the building of showcases and decoration.