Acidic or alkaline? Now you can distinguish between what paper or board is suitable for conservation with the stroke of a pen. The solution will turn a shade of purple on paper with a pH of 6.5 or higher. Any other color would indicate a pH lower than 6.5, thereby acidic and unsuitable for artwork that is meant to last. Paper can be respectably long lived if is pH is as low as 6.0, especially if it is well made and carefully used and stored. In order to last for centuries in today's polluted air, it must have an alkaline reserve and this usually means a pH of 7.0 or greater. Details: Easy to use Instant results Indicator solution of chlorophenol red Note: Unreliable results may occur on colored or coated papers