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Assessing Your Pulp and Paper

March 16, 2021

This information is reprinted from the For Beginners column of Hand Papermaking Newsletter #88 (October, 2009).

When you are starting out as a papermaker, it can be a challenge to judge when you’ve completed certain steps of the papermaking process, such as when your pulp is done, or when your paper is completely dry. Other aspects require some testing no matter how familiar you are with the process. For example, in order to make sure that your paper is archival, you need to be able to measure the pH of your pulp. Here, we will address several tests for assessing your pulp and paper.

1) Pulp “Doneness”

How can you tell if your pulp is ready for sheet forming? After some practice, I am able to tell through a combination of timing the beating, eyeballing the pulp, and sticking my hand in it to assess its fluffiness. But when I’m unsure, I might use the jar test. Take a small clear jar—a baby food jar is of sufficient size. Fill two-thirds to three-quarters of the jar with water; then add a pinch of processed pulp (without actually pinching it and compressing the fibers!). Shake the jar to disperse the fibers through the water. Do they disperse evenly? You are looking for a fine cloud of suspended fibers, without clumping or knots. If you notice clumping, beat your fiber longer until it disperses.

2) pH

If you are aiming to make an archivally sound paper, assessing the pH of your pulp with a basic paper strip test, known as a litmus test, can be useful. Even if you are working with fibers that have been cooked with a caustic (such as soda ash) to achieve a neutral pH, if the water you add to hydrate and beat the fibers is not pH neutral, the overall acidity or alkalinity of your paper may be affected. It should also be noted that fibers cooked in caustic that have not been adequately rinsed may still be strongly alkaline. The pH test strips assess your pulp on the standard scale of 0 to 14, where 7 is pH neutral. Simply dip the paper strip into the pulp and allow it to sit for a minute; the paper changes color to indicate the pH. Compare the color of your strip to the color chart provided with the strips. A slightly alkaline pH reading of 8-9 is ideal to buffer the paper’s pH against acidity in the environment.

What can you do if your paper is too acidic? Calcium carbonate is an alkaline buffer that can be added to help neutralize your pulp. Note that this substance is also a filler that makes for a more opaque paper. If you determine that your water source is adversely affecting the neutrality of your pulp, it may be time to research some sort of water filtration.

3) Paper Dryness

However you are drying your paper, it can be easy to confuse dry-to-the-touch with dry paper, particularly when you are impatient and enthusiastic about your new paper. One touch test to use when testing paper for dryness is a temperature test. If the paper feels cool to the touch, it is not yet fully dry. Give it some fresh blotting material and put it back under weight (if it is drying under restraint) for another day. You might also take one sheet out and expose it to the air to see whether it curls. If it warps quickly, leave the rest of the paper to dry longer.

Keeping these three tests in mind, you will be able to prevent some of the common problems faced by the beginning papermaker.

by Mary Tasillo