Transparent paper distorted by prolonged rolled storage, before treatment
Part 1 of this article described the manufacture of paper and measures taken to produce a flat product. In Part 2, we look at some of the ways post-production environment and handling can cause paper to distort.
Changes in Moisture Content: Exposure to normal cycles of temperature and humidity can relax the inter-fibre bonds and tensions in even the most heavily sized paper. If only one side of the paper is exposed to moisture, that side will expand and cause the sheet to curl. As the sheet dries, it will first flatten and then, perhaps, continue to curl in reverse toward the previously wet side, because stretch tensions created in the original manufacture have been released and that side has now shrunk. Paper-making defects become apparent as these stretch tensions are released.
Application of Media: Water-based media can relax or break the stretch tensions created in the manufacture. Some watercolourists pre-stretch their paper to prevent curling and cockling. Others may like and even encourage such dimensional changes.
Papers used for intaglio prints are dampened before printing, allowing the softened sheets to sink into the recessed (etched or engraved) and inked areas of the plates. The pressure of printing creates a stretched plate mark and can sometimes stretch the printed area of the paper so that it becomes 3-D. Subsequent drying can also cause curl, undulations and edge cockles. These types of distortion are considered integral to the piece.
Oil-based media can prevent the expansion and contraction of paper exposed to normal atmospheric conditions. Un-inked areas expand with increased moisture content, moderately inked areas may have restricted movement and heavily inked areas are prevented from moving.
Mounting and Storage Methods: A number of distortions may result from how paper is mounted or stored:
- Hinges along the width and length of an artwork can restrict paper expansion, causing bulges between hinge attachments.
- Tight framing can restrict paper expansion, resulting in accordion ripples.
- Papers edge-glued to secondary supports can develop corner draws or buckling.
- Overall mounting (e.g., gluing or dry-mounting to a more rigid backing) can develop weak spots that result in bubbles or blisters when the expanding paper breaks free of the adhesive.
- Prolonged rolling, especially small-diameter rolls, can create a semi-permanent (and sometimes permanent) curl as intermolecular bonds shift to accommodate the new paper shape.
Water Damage: Direct water contact releases uneven tensions inherent to the paper. Subsequent drying results in localized cockles and curls.
Inherent Vice: Some papers are especially susceptible to distortion. Japanese papers made with gampi fibres and western transparent papers are two such examples. Special care must be taken to keep these kinds of paper in very stable environments.
Previously: Next issue: Distortions and Dimensional Changes in Paper: Causes, Mitigations and Appreciation (Part 1)
Next issue: Next issue: Distortions and Dimensional Changes in Paper: Causes, Mitigations and Appreciation (Part 3)