Washing is a routine treatment in paper conservation and the pH of bath solutions is often measured with inexpensive, widely available pH strips. However, the low-ionic strength of wash baths may pose challenges for their measurement using both strips and meters. This study investigated the limitations of this testing practice. Precision and trueness of pH strips were compared against values obtained with a meter fitted with a combination low-ionic strength electrode. Based on common washing procedures, four aqueous systems were tested: deionized water, saturated calcium hydroxide, ammonium hydroxide, and calcium carbonate in carbonated deionized water. A second set of measurements was taken after adding a commercial ionic adjuster (diluted potassium chloride) to each aqueous system. Both sets of measurements showed that the pH strips had limited trueness. Future research will explore a wider array of pH strips to assess whether any should be employed in practice. Poster presented at the 2026 AIC-CAC Annual Meeting (Montreal, April 28-May 2, 2026).
Naor et al. (Tue,) studied this question.