The conservator faced with the need to assess the acidity of a paper support cannot resort to the more rigorous cold extraction methods. The surface electrode permits the non-destructive measurement of pH. The resultant data, however, must be interpreted with caution since the nature of the paper support and any additive materials will have a profound effect on the measured pH. It is further noted that extreme care must attend the conditioning of the surface electrode prior to measurement. Conditioning is optimum when the electrode is immersed in a buffer of pH near that of a test reading of the paper surface.