Drying and Pressing
Part of Paper Making
How to press water from freshly formed sheets and dry them flat — the final steps that determine paper flatness, smoothness, and permanence.
Why This Matters
Pressing and drying transform a fragile wet fiber mat into a durable, flat sheet of paper. Done correctly, pressing removes most of the water mechanically — which is much faster and requires less energy than drying alone — and consolidates the fiber mat into a dense, smooth surface. Drying then removes the remaining moisture while controlling how the sheet shrinks and whether it dries flat or warped.
In a post-collapse setting, the pressing and drying stages determine throughput. A good press setup allows you to recycle felts quickly and keep the mold in continuous use. Poor drying — sheets that wrinkle, warp, or stick to surfaces — wastes fiber and time. Since paper production is labor-intensive from start to finish, losing sheets in the final stage is especially demoralizing and costly.
Understanding the physics of what happens during pressing and drying — how fibers bond, how water moves, how tension causes warping — allows you to design appropriate equipment from available materials and to troubleshoot problems before they destroy a batch.
The Physics of Pressing
When wet sheets are stacked between felts and pressed, two things happen simultaneously:
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Water expression: Pressure squeezes water out of the fiber mat, through the felt, and out of the press. Mechanical water removal is approximately 10 times faster than evaporative drying for the same energy input. A good pressing removes 40 to 60 percent of water from the sheet.
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Fiber consolidation: Pressure collapses the three-dimensional fiber mat into a flatter, denser structure. Fibers that were bridging across gaps in the wet mat are pushed into contact with neighboring fibers, forming additional hydrogen bonds. This increases sheet strength and density dramatically — a pressed sheet is noticeably stronger than an unpressed sheet dried from the same wet state.
The key variables are pressure magnitude (how hard you press) and dwell time (how long the press is held). More pressure is not always better — excessive pressure can crush fiber structure and produce dense, brittle paper. The goal is sufficient pressure to remove water efficiently and consolidate fibers without destroying the sheet’s structure.
Building a Simple Press
Lever Press (Recommended for Small Scale)
A lever press uses a long wooden beam as a lever arm, with a fulcrum and a pressing plate. Construction requires:
- Two heavy posts or timbers, 10 to 15 cm diameter, anchored vertically
- A crossbeam connecting the posts at the top, forming an arch
- A pressing platen: a flat, smooth board slightly larger than your mold
- A lever arm: a heavy timber 2 to 3 meters long
- A fulcrum: a log or stone over which the lever pivots
The post stack (alternating felts and paper sheets) sits on a flat lower surface. The pressing platen sits on top of the post. The lever pivots over the fulcrum and presses down on the platen. A person’s weight on the lever arm provides the pressing force. For a 3-meter lever with a fulcrum at 50 cm from the press end, a 70 kg person standing at the far end applies approximately 420 kg of force — sufficient for a small post.
Screw Press (Better for Larger Operations)
A screw press uses a large wooden screw (carved by hand or made from a log with a spiral groove) to apply controlled, sustained pressure. Medieval European paper mills all used screw presses. They apply more uniform pressure than lever presses and can be left under tension without requiring a person to hold the lever.
Carving a large wooden screw requires skill and appropriate hardwood. Oak, ash, or similarly dense hardwoods work best. The screw and its matching threaded box must be carved to the same pitch. This is achievable with basic hand tool skills but requires patience — plan for several days of carving.
Stone Weight Press (Simplest)
Stack your post, place a flat board on top, and pile heavy stones on the board. Works adequately for small batches if the stones are flat and the pressure is distributed evenly. The limitation is that pressure cannot easily be increased once stones are placed, and uneven stones create uneven pressure.
Step-by-Step Pressing
Step 1: Build the Post
On the lower press surface, lay a flat couching board. Stack felts and sheets alternately: felt, sheet, felt, sheet, up to 15 to 20 sheets per post depending on your press capacity. Ensure sheets are centered on their felts and that each felt extends beyond the sheet edge on all sides by at least 2 to 3 cm. Place a final flat board on top.
Step 2: First Press
Apply maximum available pressure. Hold for 5 to 10 minutes. During this time, water actively flows from the stack — you can see it pooling around the base of the press.
Step 3: Remove and Repost
Release the press. Separate the post one layer at a time. Remove each sheet from its felt. Note: the sheets are now firmer and easier to handle without tearing, but still damp. Lay the removed felts flat to drain slightly.
Repost: reassemble the post with fresh dry felts if available, or with the original wrung-out felts. Apply pressure again for another 5 to 10 minutes. The second pressing removes additional water that migrated back into the sheet during the brief release.
Step 4: Exchange Felts
For the best results, a third pressing with completely fresh, dry felts removes still more water. Each successive pressing with drier felts draws more moisture from the sheets. Three pressings are the minimum for quality writing paper; two may suffice for rough paper.
Drying Methods
After pressing, sheets contain approximately 30 to 40 percent water by weight. Drying must remove this water without causing warping, cracking, or sticking.
Board Drying (Eastern Method)
Wet pressed sheets are brushed directly onto smooth wooden boards and allowed to air-dry in place. As the sheet dries, it shrinks and bonds to the board surface, creating tension that keeps the sheet flat. When fully dry, the sheet releases cleanly.
Board preparation: Brush boards lightly with dilute starch paste (or rice water) to prevent the sheet from bonding permanently. Too much paste and the sheet will not release; too little and it may bond so firmly it tears on removal.
Application: Use a broad, soft brush to smooth the wet sheet onto the board, working from the center outward to chase out air bubbles.
Drying time: 4 to 24 hours depending on temperature, humidity, and air circulation. Do not force-dry with heat — rapid drying causes warping.
Rope Drying (Western Method)
Pressed sheets are draped over rope or wooden dowels and allowed to air-dry suspended. Simple to set up and requires no boards, but produces paper with a slight crease at the draping point and occasional curling as the sheet dries unevenly.
To minimize crease marks, drape the sheet over the rope while it is still damp and slightly limp, then smooth it flat. As it dries, the crease softens. For sheets that will be pressed flat after drying (see finishing), rope drying is acceptable.
Hanging on Pegs
String multiple short ropes or thin poles between two support posts, like a multi-level clothesline. Hang sheets individually from the rope, overlapping slightly if necessary (though overlapping causes sticking — allow space between sheets if possible).
Heated Drying Rooms
In pre-industrial paper mills, heated drying rooms (lofts above ovens or kilns) allowed year-round production regardless of outdoor temperature. You can achieve this with any heated enclosed space — a room with a fire, a kiln loft, or a greenhouse-style structure with good ventilation.
Drying temperature should be warm but not hot: 30 to 40°C is ideal. Above 60°C, paper dries too quickly, with the surface drying and hardening before interior moisture can escape, trapping stresses that cause warping and cracking.
Troubleshooting Drying Problems
Sheets dry wavy and cockled: Uneven moisture removal. Either the pressing was insufficient (more water on one side), or the sheet was draped unevenly during drying. Solution: dampen slightly and press flat under weight overnight.
Sheets stick to boards and tear on removal: Too little sizing on board, or sheet dried while still too wet (bonded deeply). Prevention: ensure boards are properly prepared. Recovery: dampen the stuck sheet from the back of the board and peel slowly.
Sheets curl into tubes: Dried too quickly with one side exposed to air. Paper curl always curves toward the side that dried first. Solution: dampen both sides and press flat under weight.
Sheets are brittle and crack: Fiber was over-beaten, producing very short fibers that do not form a flexible mat. Or the sheet dried too hot, degrading fiber. Prevention through process control; no recovery for already-damaged sheets.
Sheets have watermarks or stains: Contamination in the pulp or vat water. Rust from metal containers, vegetable tannins from inadequately rinsed cooking water, or mold growth on couching felts. All require addressing the source rather than the symptom.
Flattening After Drying
Even well-dried sheets benefit from flattening after drying. Dampen both surfaces of each sheet lightly (breathe on them, or pass through steam), then stack sheets together between two flat boards with a heavy weight on top. Leave overnight. Sheets will absorb each other’s slight moisture variations and dry perfectly flat.
This final flattening is especially important before writing or printing — a slightly cockled sheet makes writing uneven and can jam a printing press.
Storage After Drying
Dry paper stored in dry conditions lasts centuries. The enemies are moisture, insects, mold, and acid. Store finished paper:
- In a dry, ventilated space away from direct ground contact
- Wrapped in cloth or stored in sealed wooden boxes to exclude insects
- Away from acidic materials (fresh wood, certain fruits, some minerals) that off-gas acids over time
- Flat, not rolled, unless rolls are absolutely necessary — rolled storage creates curl that requires dampening and re-pressing to remove
With proper pressing and drying, your community’s paper will be a durable, reliable medium for the knowledge you need to preserve and transmit.