Leafcasting for Paper Conservation

1. What Is Leafcasting?

Leafcasting is a paper-conservation technique used to fill missing areas of damaged sheets with new paper fibres.

The method is related to papermaking.

A damaged sheet is placed on a screen within a leafcasting machine. A dilute suspension of paper fibres is introduced, and water is drawn through the screen by gravity, suction or a controlled combination of both.

Because the intact paper blocks the flow, fibres preferentially deposit in:

• holes;
• missing margins;
• tears;
• lacunae;
• insect-damaged areas.

After drying, the deposited fibres form a new paper fill mechanically integrated with the original sheet.

AIC Book and Paper Group literature describes leafcasting as a way to stabilise paper weakened by holes or ragged borders and emphasises that the amount of pulp is critical to achieving satisfactory results.

2. What Problems Can Leafcasting Address?

Leafcasting can be particularly useful for:

• insect-damaged manuscripts;
• documents with extensive edge losses;
• maps and large sheets with multiple lacunae;
• bound text blocks after disbinding where many leaves require similar repair;
• weakened paper that needs continuous fibre fills around irregular losses.

It can be more efficient than individual hand infills when a large number of losses must be repaired.

However, efficiency is not the only criterion.

The object must first be suitable for immersion or controlled wet treatment.

3. Material Assessment Comes First

Leafcasting usually involves substantial contact with water.

Before treatment, examine:

• paper fibre type;
• degree of brittleness;
• previous sizing;
• inks;
• pigments;
• stamps;
• annotations;
• watercolours;
• adhesives;
• previous repairs;
• mould damage;
• tears and fragments.

Media solubility

Water-sensitive inks or pigments can bleed, feather or migrate.

Testing should therefore be performed before immersion.

When media is too vulnerable for full wetting, alternative hand-pulp or local suction methods may sometimes be more appropriate.

AIC literature notes that hand pulp application can provide greater local control and can be useful when complete immersion is not safe.

4. How Leafcasting Works

The physical principle is straightforward.

Step 1 — Position the sheet

The object lies flat on a supporting screen.

Step 2 — Introduce pulp slurry

A suspension of dispersed paper fibres is added to the tank.

Step 3 — Draw water through the support

The machine creates downward flow through the screen.

Step 4 — Fibres deposit in losses

Where original paper is present, flow resistance is higher.

Where paper is missing, water passes through and carries fibres toward the open area.

Step 5 — Fibres interlock

As water leaves, deposited fibres form a sheet structure.

After pressing and drying, fibre-to-fibre bonding gives the infill mechanical integrity.

The treatment is therefore not simply “gluing paper pulp into a hole.”

5. Pulp Selection

The repair pulp should be selected according to:

• fibre type;
• fibre length;
• beating;
• colour;
• opacity;
• thickness;
• ageing behaviour.

Conservators may use fibres such as:

• cotton;
• linen;
• abaca;
• suitable high-quality cellulose pulps;
• blends developed to match the original sheet.

The ideal pulp is not necessarily chemically identical to the original paper.

It should provide a compatible visual and mechanical repair.

Colour matching

Pulp may be toned to reduce visual contrast.

The objective is normally not to create an invisible falsification.

A conservation repair should remain sympathetic and legible under appropriate examination.

6. Calculating Pulp Quantity

One of the most important technical variables is the amount of fibre introduced.

Too little pulp can produce:

• thin fills;
• weak edges;
• incomplete losses.

Too much pulp can produce:

• thick patches;
• ridges;
• excess deposition;
• uneven drying;
• visual disruption.

AIC literature on leafcasting has described systems for measuring the exact area of loss and calculating the amount of pulp required.

Modern systems may use:

• digital imaging;
• area calculation;
• basis weight or target thickness;
• calibrated pulp concentration.

A simplified logic is:

Loss area × Target paper mass per area → Required dry fibre mass

The slurry concentration is then used to determine the liquid volume required.

Accuracy is particularly useful when many leaves are treated.

7. Preparing the Paper

Preparation may include:

• surface cleaning;
• removal of damaging old repairs;
• testing media;
• controlled washing;
• deacidification;
• fragment alignment.

Not every object needs every step.

The treatment plan should define the purpose of each operation.

Wetting

Uniform wetting helps the sheet lie flat and can support even fibre deposition.

However, differential expansion can occur when degraded areas absorb water differently.

Fragile material may require support during transfer.

8. The Casting Process

A typical machine workflow may be:

Assess → Prepare → Wet → Position → Calculate Pulp → Cast → Drain → Inspect → Size if Required → Dry

Positioning

Fragments and torn edges should be aligned before the pulp is introduced.

Masking

Masks or deckles may limit the area in which new paper is formed.

This helps prevent unnecessary fibre deposition around the object.

Suction

Controlled suction draws water through the screen.

The flow should be strong enough to produce even fibre deposition but not so abrupt that fragments move or distorted paper is damaged.

Inspection before removal

Before lifting the sheet, check:

• whether all intended losses are filled;
• whether fragments have shifted;
• whether pulp has deposited over original media;
• whether the new fill has reasonable thickness.

9. Sizing and Strength

Freshly cast fibres may require sizing depending on the treatment objective and pulp.

Sizing can:

• alter surface strength;
• reduce absorbency;
• improve handling;
• integrate weakened paper.

Possible conservation sizes include suitable cellulose ethers, gelatin or other materials selected for the object.

Sizing is not automatically required after every leafcast.

The decision depends on:

• original paper;
• new pulp;
• intended handling;
• additional lining or repair.

10. Drying and Flattening

Drying strongly influences the final result.

Poor drying control can produce:

• planar distortion;
• cockling;
• edge tension;
• offsetting;
• adhesion to drying materials.

A treated sheet may be:

• blotted;
• pressed;
• dried under controlled restraint;
• dried between suitable felts or blotters;
• subsequently flattened.

The exact method depends on paper strength, media and conservation objectives.

11. When Leafcasting May Not Be Appropriate

Leafcasting is not a universal repair method.

Caution is required with:

• highly water-soluble media;
• paper that cannot tolerate immersion;
• friable pigments;
• heavily coated paper;
• composite sheets;
• extremely weak fragments that cannot survive wet handling;
• objects where the aesthetic effect of fibre infill is undesirable.

Other methods may include:

• Japanese-paper repair;
• hand pulp infill;
• lining;
• local suction treatment;
• encapsulation;
• limited handling with supportive housing.

The conservator should select the least interventive method that meets the treatment goal.

12. Treatment Quality

A good leafcast repair should be evaluated for:

Fill completeness

Losses are filled where intended.

Thickness

The new paper is not excessively thick or thin.

Fibre integration

The fill attaches reliably to the original edge.

Surface quality

There is no unnecessary pulp deposition over media or sound paper.

Colour

The infill is visually compatible with the object.

Dimensional stability

The sheet dries without unacceptable distortion.

Handling strength

The treatment gives enough support for intended use without making the object unnaturally rigid.

13. Production Workflow for Large Projects

Leafcasting can be efficient for collections with repeated paper-loss problems.

A larger programme should define:

• selection criteria;
• media testing;
• pulp recipes;
• colour groups;
• calculation method;
• batch tracking;
• drying capacity;
• post-treatment QA.

The leafcaster itself may not be the throughput bottleneck.

Drying, washing, sizing, documentation and conservator assessment can require more time than casting.

System planning should therefore consider the complete laboratory workflow.