pH Testing Pen


Test products for acidity.

The pH testing pen is a simple tool to easily and instantly spot test books, documents, paper and card for acidity.

Used by archivists, librarians and conservationists to identify acidic or alkaline paper. Conforms to ASTM d-4236.

The acid content in paper determines its life expectancy. The acid content is measured on a pH scale:

  • pH 3-6  very acidic with a short life expectancy
  • pH 7     neutral and classed as acid free - lasts 200 years
  • pH 14   alkaline with a very long life expectancy - 500 years or more

Acid free paper (pH 7.0 and above) has a high degree of durability and permanence and will last for up to 200 years under normal use and storage conditions. It will not discolour or become brittle with normal handling.

See our acid free papers Acid Free Paper

How to use the pH testing pen:

Draw a small line or place a spot in an unobtrusive area of the material being tested. Dries in seconds.

If the result indicates pale yellow (below 6.5) the paper is acidic.

If the result indicates pale purple, (above 6.8) the paper is neutral or alkaline. This is the result required for long term conservation.

If the result indicates a tan colour (combining yellow and purple) the paper is of intermediate acidity.

Please note: unreliable results may occur on coloured or coated paper.