With a simple swipe of Lineco's pH testing Pen, you can determine whether the paper and board you are using may be acidic. Easy to use, simply draw a small line on the material you wish to test. The line drawn will turn purple on most papers if there is an indication of pH neutrality. A clear or yellow color indicates the material may be unsuitable for conservation purposes. Paper can be reasonably long-lived if its pH is 6.0 or higher, 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. Please note: This is a pH indicator only. Unreliable results may occur on colored, coated, or unbuffered materials.