Mold and Deckle
Part of Paper Making
Building and maintaining the mold and deckle — the two-piece frame that forms each sheet of paper and determines its size, quality, and characteristics.
Why This Matters
The mold and deckle are the most important tools in a paper mill. Every sheet of paper produced passes through them. Their quality directly determines the quality of the paper: a mold with an uneven screen produces sheets with ridges and thick spots; a warped mold produces sheets that do not drain evenly; a deckle with gaps allows pulp to escape and creates ragged, uneven edges.
Making a good mold and deckle requires basic carpentry skills and access to a few specialized materials — primarily a fine-weave screen or mesh for the mold surface. In a post-collapse context, the availability of screen material may be the primary constraint on paper production. Understanding what makes a good screen and how to improvise with available materials determines whether your community can build a working paper mill or must rely on other recording media.
The mold and deckle also determine your standard sheet size. Whatever size you build becomes your community’s standard — and once you begin binding books and building shelving around that size, it becomes a long-term constraint. Choose your dimensions deliberately.
The Two Components
The Mold
The mold is a rigid rectangular frame with a fine screen stretched tightly across it. The screen catches fiber when the mold is drawn through the pulp vat, forming the sheet. Water drains through the screen, leaving the fiber behind.
The mold must be:
- Rigid: Any flex during use disrupts the fiber mat and produces uneven sheets
- Waterproof: The frame must not absorb water, swell, and change dimensions
- Flat: The screen surface must be planar — any bow or warp creates thick and thin zones
- Durable: The mold is used repeatedly; joints must withstand constant wetting and drying
The Deckle
The deckle is a matching frame with no screen — it simply sits on top of the mold during dipping and defines the edges of the sheet. Its inner dimensions match the outer dimensions of the mold screen area exactly. When the mold is lifted from the vat, the deckle contains the pulp on the screen until most water has drained, then it is removed before couching.
The deckle must be:
- Precisely fitting: Any gap between deckle and mold allows pulp to flow out, creating ragged edges
- Smooth inner edges: Rough inner edges create irregular sheet edges
- Same dimensions as mold: The two must be a matched pair — deckles and molds are not interchangeable between different frames
Choosing Sheet Size
Standard sheet sizes reflect the typical uses of paper in a rebuilding community:
| Size (cm) | Practical Use |
|---|---|
| 20 × 25 | Letter size, notebooks, personal correspondence |
| 25 × 35 | Standard document, journal pages |
| 35 × 50 | Ledger, large technical drawings |
| 50 × 70 | Maps, large posters, book folios |
Consider: two sheets of your standard size folded together should create convenient book pages. A 35 × 50 cm sheet folded once makes a 25 × 35 cm folio — a useful book format. Plan your sheet size with downstream bookbinding in mind.
Larger molds are harder to control during dipping and require deeper vats. Smaller molds produce sheets too small for many purposes. 25 × 35 cm is a good starting point for a general-purpose community paper mill.
Frame Construction
Materials
Preferred: Dense, straight-grained hardwood — oak, ash, maple, or similar. Avoid soft woods (pine, cedar) for the outer frame as they absorb water and swell with use, eventually distorting the mold. However, softwood can be used for internal support ribs if they are well-sealed.
Alternative: Bamboo, where available, makes excellent mold frames. It is naturally water-resistant, lightweight, and dimensionally stable. Split bamboo laid parallel in one direction forms a traditional Japanese mold screen (the su in Japanese hand papermaking).
Joint Design
Corner joints must be both strong and watertight. Options:
Mortise and tenon: Cut a tenon (projecting tongue) on the end of each side piece and a matching mortise (slot) in the adjacent piece. Glue with hide glue or pine pitch. This is the traditional and strongest joint for mold frames.
Half-lap joint: Each corner piece has half its thickness removed, and the pieces overlap and are glued and pinned. Slightly weaker than mortise and tenon but easier to cut.
Dowel joints: Drill matching holes in corner pieces and glue with wooden dowels. Simpler but less strong.
Reinforce all joints with wooden pins (wooden nails driven through the joint at 90 degrees to the glue line). Metal nails will rust and stain paper — use wood, bone, or hardwood pins.
Sealing the Frame
After construction and before attaching the screen, coat all wooden surfaces with a water-resistant sealant. Options:
- Beeswax: Melt and brush on, repeat 3 times. Excellent water resistance, flexible, natural.
- Pine pitch: Mixed with a small amount of fat or tallow for flexibility. Very waterproof.
- Linseed oil: Several coats applied over several days, with drying time between coats. Less waterproof than wax or pitch but easier to apply.
Internal Support Ribs
For molds larger than 25 × 35 cm, the screen needs internal support to prevent sagging. Cut thin wooden ribs (5 mm × 10 mm) and glue them across the short dimension of the mold, spaced 5 to 8 cm apart. These ribs are called “chain lines” in Western mold making — their shadows appear as faint parallel lines in light-transmitted through the finished paper (this is the origin of “laid paper”).
Seal support ribs along with the frame before screen attachment.
Screen Materials and Attachment
Woven Screen (Western Mold)
The traditional Western mold uses a fine woven mesh. In post-collapse conditions, options include:
| Material | Mesh Size | Notes |
|---|---|---|
| Silk cloth | Fine | Excellent but rare |
| Fine linen or cotton | Medium | Good for most paper weights |
| Brass or bronze wire cloth | Fine | Best durability if metalworking available |
| Woven horsehair | Medium | Traditional in some Asian traditions |
| Fine plant fiber weave | Variable | Works if weave is tight and even |
The mesh must be fine enough that wet fiber cannot pass through it but water can drain quickly. A mesh that passes water too slowly makes the formation motion awkward and produces uneven sheets. Test a screen by holding it over a container and pouring a cup of water through — it should drain in under 5 seconds.
Attaching the screen: Stretch the screen material over the mold frame as tightly as possible without distorting the weave. A loose screen sags under the weight of wet fiber, creating a dish shape that produces thick-center sheets. Lash the screen to the frame with fine cord, stitching through the screen and around the frame edge, pulling firmly at each stitch to maintain tension. Seal the perimeter with wax or pitch to prevent fiber from accumulating at the edge joints.
Split Reed or Bamboo Screen (Eastern Mold)
Japanese and Chinese molds use flexible screens made from thin, evenly split bamboo or reed strips lashed together with fine thread. These “su” screens are not permanently attached to the frame — they rest on it and can be removed for separate storage and drying, which extends their life.
Making a su screen requires splitting bamboo or reed into strips approximately 1 mm wide and 0.5 mm thick, then lashing them parallel with fine thread at regular intervals. The result is a flexible screen that can be rolled up for storage.
Building the Deckle
The deckle is simpler than the mold. Construct a plain rectangular frame with the same outer dimensions and joint method as the mold. The inner dimensions of the deckle should match the inner dimensions of the mold screen area exactly.
The key fit: when the deckle sits on top of the mold, there should be no visible gap between them, and the deckle should not rock. Test the fit by placing the deckle on the mold and looking down at the joint from above while moving slightly — you should see no light through any part of the joint.
If gaps exist, line the bottom inner edge of the deckle with a thin strip of tightly woven cloth, leather, or compressed plant fiber, glued in place. This soft gasket material conforms to the mold surface and seals the joint.
Maintenance and Repair
After each session: Rinse mold and deckle with clean water. Remove any fiber accumulation from the screen, especially at the edges where it builds up. Use a soft brush — never scrape a screen with metal or anything that might cut it. Lean both pieces on edge to drain and dry, not flat on one side (flat drying can warp the frame).
Drying: Allow to dry completely between sessions. Damp storage leads to mold growth that stains future paper and weakens wood joints.
Screen repair: Small holes or torn sections in the screen can sometimes be repaired by weaving in replacement thread or by patching with a small piece of matching mesh, secured with thread and sealed with wax at the edges. A patch produces a visible defect in the paper (a thinner spot where the patch is thicker than the mesh) — acceptable for rough paper but not for fine documents.
Frame straightening: A warped frame can sometimes be straightened by wetting thoroughly, weighting flat on a surface, and allowing to dry under weight. Deep warps may require cutting the joint and rebuilding.
A well-made mold and deckle, properly maintained, can produce thousands of sheets over several years. The investment in building them correctly from the start is repaid many times over.