Why Test For Acidity in Papers?
Acid in storage materials or on the paper something is made from or printed or painted onto, can migrate to nearby papers, fabrics, art work and photos, turning fabrics and papers brittle, and changing colors in papers, fabrics and photos.
Inexpensive pH test pens from art, photography and scrapbook suppliers can be used to text papers for acidity. The pen is used to make a mark on the paper, and the mark will change color, in a range from blue through green to yellow to indicate the paper's acidity. The color of the ink after the change is checked against a chart which comes with a pen to identify how acid the material is. Remember that paper can absorb acid from your hands, so test areas of the paper which have not been handled, and also remember that paper if left in the atmosphere, can absorb acidity from its environment or from acidic materials it comes in contact with.
Papers which start off acid free, may absorb sufficient amounts of acidity from the atmosphere to test as being acidic. Papers labelled as acid free may also contain lignin which can change the acidity of the paper as it breaks down. Lignin testing pens which turn orange on contact with lignin based papers are also available from museum and archival supply stores.
Most pH testing pens can be used with a range of porous materials. These include paper, stationary, stickers, packing tissue, permeable textiles (cotton, canvas and silk) and gesso and art mediums