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CURRENT COLUMN

Seeing in Different Ways: A Liz Magor Backpack Project
Seeing in Different Ways:
A Liz Magor Backpack Project

Why Paper Discolours (Part 2)
Why Paper Discolours (Part 2)

Why Paper Discolours (Part 1)
Why Paper Discolours (Part 1)

Mending a Tear in an Aboriginal Drum
Mending a Tear in an Aboriginal Drum

Distortions and Dimensional Changes
in Paper (Part 3)
Distortions and Dimensional Changes
in Paper (Part 3)


Distortions and Dimensional Changes
in Paper (Part 2)


Distortions and Dimensional Changes
in Paper (Part 1)

After treatment
Oscar Cahén: Innovative Conservation
for an Innovative Artist

Structural
Rigid Water Gels: New Treatment Options for Paper Conservators

Structural
Structural Remedies for Canvas Paintings

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

Photos
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

Butterfly
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

Spots on print caused by Fenton Reaction

Spots on print caused by Fenton Reaction

Iron in Paper: Problems and Current Solutions - Part 1

by Rebecca Pavitt
www.fineartconserve.com

Discoloration and foxing (scattered dark spots) in paper are some of the most common reasons that clients bring paper artifacts to a conservator for restoration. These conditions are often cleaned with oxidative bleaches. While such treatments are generally quite effective, if iron is present in the paper oxidative bleaching can actually make the discoloration worse. Part 1 of this article describes the problems that iron can cause in paper; Part 2 will describe some solutions that are making their way into the paper conservator’s repertoire.

Iron is sometimes, but not always, present in paper. When iron is present in paper, it can sometimes, but not always, cause discoloration and foxing. Because iron is a catalyst, traditional oxidative bleaching methods used by conservators to reduce discoloration can, after an incubation period of a few weeks or months, actually accelerate discoloration, making a bad situation worse. Iron can exist in many forms. As anyone with a car, boat or carbon steel kitchen knife knows, metallic iron (Fe) is not particularly stable; it likes to oxidize into a broad array of black, white, uncoloured and multicoloured compounds, including rust.

Iron can exist in more than one oxidation state. The most common oxidation states are Fe(II) in which metallic iron has lost two electrons and Fe(III), where metallic iron has lost three electrons. Fe(III) is the least reactive form of iron but both Fe(III) and metallic iron can, under the right environmental circumstances, convert to the very reactive Fe(II) form.

Iron can be introduced into the paper intentionally, as in the case of inks and other media, or as unintended contaminants. Iron can be found in unpurified wood pulp, the water used to make the paper, low grade chalk fillers, rosin and papermaker’s alum. Bits of metallic iron that rub together and break off from paper-making machines also find their way into paper sheets.

Traditional methods of treating discoloured paper include oxidative bleaches that contain or generate peroxides (for example, hydrogen peroxide, sodium perborate and light). Peroxides react with and solublize the damaged and discoloured portions of the cellulose molecule, allowing them to be washed away. Although these oxidative bleaches can be very effective, Fe(II) can (but not always) catalyze the peroxides to trigger the dreaded Fenton Reaction. In a few weeks or months, the previously cleaned paper can become heavily spotted and discoloured. This situation is obviously something to be avoided, but its occurrence cannot always be predicted.

How, then, to avoid such a situation? Is it possible to determine if paper contains iron before embarking on oxidative bleaching treatments?

There are visual and chemical tests for detecting iron in paper before treatment but, unfortunately, these tests are not foolproof. Iron particles can be hidden deep within the paper sheet; oxides may not be concentrated enough to give positive reactions when tested with chemical reagents or they may be unevenly distributed in the paper sheet, leading to false negative test results.

What, then, is the best way to safely reduce discoloration in paper that may contain iron, detected or not? And once discoloration has been reduced, how can paper be protected from residual iron that may have been left behind? There are no simple answers to these questions, but my research over the past year has given me some leads which I will share in the next article.

Previously: Caring for Public Collections: A Condition Survey
Next issue: Iron in Paper: Problems and Current Solutions – Part 2

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 Thu, Apr 4, 2013