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Rigid Water Gels: New Treatment Options for Paper Conservators

Structural Remedies for Canvas Paintings

Organizing and Preserving Collections - Part 4: Digital-based Material

Organizing and Preserving Collections - Part 3: Photo-based Material

Organizing and Preserving Collections - Part 2: Paper-based Material

First Steps
Organizing and Preserving Collections - Part 1: The First Steps

Natural Dyes
The Use of Natural Dyes in Textile Conservation

A Relocation Project

Challenges of Preserving Contemporary Artwork

Preserve Your Investment through Art Conservation

A Project Completed: Heritage Preserved

Old and New Methods for Cleaning Paintings

I Can See Clearly Now – Or Can I? Part 2

I Can See Clearly Now – Or Can I?

The E.J. Hughes Mural: An Expanded Project

Is She or Is She Not an Emily

Treating Art with Sensitive Media

Malaspina Mural: An Update

For the Artist: Testing Your Materials

Conservator as Art Historian

Alum Sizing and the Art of W.J. Phillips

Treatment of an Elizabeth Keith Wood Block Print

Structural Treatment of an Emily Carr

The Treatment of a Monumental Wall Hanging

Changing Images

Preserving a Rare Record

Gold Leaf: Imitation and Genuine

The Case Against Canvas Backings

Heritage Colours: Research Discovers Original Colours

Lighting Your Art: Balancing Seeing and Protecting

The Double-Sided Emily Carr Painting

Choosing a Period Picture Frame

How to Identify a Picture Frame

Stretching Canvas and Restretching Artwork

Mounting Textiles

Aging Paintings:
Some Causes and Effects

Chine Collé Prints

What's Your Favourite Color?

Backing Removals

Rips, Holes and Tears

Filling in the Gaps

DIY – Preventative Care of Paintings

Frame it Right

Fire, Water and Smoke-Damaged Paintings

Inherent Vice

Saturated Problems:
A Water-Damaged Painting

Moldy Paper

Conserving Time

Conserving Paper: Dos and Don'ts

Repair of Textiles

Conserving Wood

Rescuing Endangered Murals

Repairing Acid-Matte Burn

Art Services & Materials
Exhibition Openings & Events

Conservation Corner Back

Distortions and Dimensional Changes in Paper: Causes, Mitigations and Appreciation (Part 1)

by Rebecca Pavitt

Handmade paper distorted by uneven drying

Handmade paper distorted by uneven drying

Paper should be flat, right? Well, sometimes. We think of paper as being two-dimensional, but actually it is a complicated 3-D web of cellulose fibres whose structure and moisture content determine its shape.

To understand why paper moves and changes shape, we must, in the immortal words of Maria von Trapp, “start at the very beginning.”

Paper is made from cellulose fibres processed by chemical and mechanical methods to a fibrillated pulp that is suspended in water and drained onto forms such as screens or racks. While draining, the forms are shaken so that the fibres distribute more or less evenly. Machine-made papers and many handmade Asian papers have a strong grain direction because most of the fibres are oriented parallel to the length of the sheet. Traditional handmade Western papers have a more random fibre distribution.

Paper grain has a great effect on the strength and dimensional behaviour of the finished product. Grained papers are strong in the direction of the grain and relatively weak in the cross-grain direction and, like a plank of wood, they have great potential for expansion across the grain. If there is a change in fibre orientation throughout the thickness of the paper (e.g., parallel distribution at the top of the sheet and random distribution at the bottom), the paper will curl.

Once free water (held between and inside the fibres) drains from the paper pulp, imbibed water (water saturating the fibre’s cell walls) is removed by pressure and evaporation. Evaporation may be accelerated by increasing heat (sun or artificial). As imbibed water is removed, the fibres are pressed together and become tightly joined by mechanical fibre-to-fibre bonds and chemical molecule-to-molecule hydrogen bonds. At the same time, the fibres shrink and stretch, creating semi-permanent tensions within the sheet. Ideally, these tensions are even and uniform, pulling the paper flat. Adhesives and sizes are usually added to the pulp or applied to the formed sheet to reinforce these fibre-to-fibre bonds and tensions.

Even drying creates flat paper. Uneven drying can result in curl (when one side of the paper dries before the other) and cockling. The most common example of cockling are the edge ripples that are formed if the edge of the sheet or roll of paper dries before the centre.

Provided all goes well at the papermaker’s, artists start with flat paper onto which they apply their media. How, then, does the flat paper end up becoming – usually not by design – 3-D?

Read Part 2 of this article in the next issue of Preview.

Previously: Oscar Cahén: Innovative Conservation for an Innovative Artist
Next issue: Next issue: Distortions and Dimensional Changes in Paper: Causes, Mitigations and Appreciation (Part 2)


 Sun, Nov 8, 2015