Pulp Preparation

Part of Paper Making

Pulp preparation breaks raw plant fibers down into a slurry of individual cellulose fibers suspended in water. The quality of this pulp — how thoroughly the fibers are separated, how much lignin has been removed, and how well the fibers have been beaten — determines everything about the finished paper.

Why Pulp Preparation Matters

Paper is only as good as its pulp. Under-cooked pulp contains tough fiber bundles that create lumpy, weak sheets. Over-beaten pulp produces dense, translucent paper that takes forever to dry. Under-beaten pulp makes loose, fragile sheets that tear easily. The pulp preparation stage is where you control paper strength, texture, opacity, and durability.

Step 1: Soaking

All fiber starts with soaking. This rehydrates dried material, begins softening the fibers, and loosens dirt and bark fragments.

Process

1. Cut or tear fiber material into small pieces (2-5 cm)
2. Place in a large container (wooden barrel, clay pot, or stone-lined pit)
3. Cover with water — use 3-4 times as much water as fiber by volume
4. Soak for 24-72 hours, stirring occasionally
5. Bark fibers soak faster; wood chips need the full 72 hours or longer

Fiber Type	Soak Time	Water Temp
Cotton rags	24-48 hours	Room temperature
Bark (mulberry, elm)	24-48 hours	Room temperature
Hemp/flax stems	48-72 hours	Room temperature
Straw	24-48 hours	Room temperature
Wood chips	72+ hours	Warm preferred

Warm Water Speeds Everything

Soaking in warm water (30-40C) reduces soak times by half. If you have a heat source, warm the soak water. Solar heating in a dark container works well in summer.

Step 2: Cooking (Alkaline Digestion)

Cooking dissolves lignin, pectin, and other non-cellulose materials that bind plant fibers together. This is the most important step for producing strong, durable paper.

Making the Cooking Liquor

Wood ash lye (most accessible):

1. Fill a barrel or bucket one-third full with hardwood ash
2. Add boiling water to fill
3. Stir well and let settle for 24 hours
4. Pour off the clear brown liquid — this is lye water
5. Test strength: a strong lye feels slippery between the fingers (like soap) and tastes sharply bitter

Slaked lime (calcium hydroxide):

1. Burn limestone or seashells in a hot fire to produce quicklime
2. Carefully add water to the quicklime (it reacts violently, producing heat)
3. The resulting slaked lime paste dissolves in water to create lime water
4. Use at 10-15% concentration (by weight of dry fiber)

Soda ash (sodium carbonate):

1. Burn seaweed or certain desert plants (glasswort, saltwort)
2. Soak the ash in water and filter
3. Evaporate to concentrate

Lye Safety

Lye is caustic — it burns skin and can cause serious eye damage. Handle with care: wear hand protection (leather or thick cloth gloves), keep away from eyes, and never splash. If lye contacts skin, rinse immediately with abundant water and then vinegar to neutralize.

Cooking Process

1. Place soaked fiber in a large pot (non-metal is best — clay, stone, or wood-lined)
2. Add cooking liquor: enough lye water to fully cover the fiber
3. Bring to a boil, then reduce to a gentle simmer
4. Cook for 2-8 hours, depending on fiber type:

Fiber Type	Cooking Time	Lye Strength
Cotton rags	1-2 hours (or skip)	Weak — rags are already mostly cellulose
Mulberry bark	2-3 hours	Medium
Hemp/flax	3-4 hours	Medium-strong
Straw	2-4 hours	Medium
Wood chips	6-8 hours	Strong

5. Stir every 30 minutes, adding water as needed to keep fiber submerged
6. The cook is done when fibers separate easily when pulled — individual strands should come apart without resistance

Testing Doneness

Take a small sample and rinse in clean water:

• Done: Fibers separate easily, feel soft and slippery, are lighter in color
• Under-cooked: Fibers still clump in tough bundles, feel stiff
• Over-cooked: Fibers dissolve to mush, very little solid material remains

Better Slightly Over Than Under

Under-cooked pulp is far worse than slightly over-cooked. Tough, un-separated fibers make terrible paper with lumps and weak spots. If in doubt, cook another hour. You can always add fresh fiber to strengthen an over-cooked batch.

Step 3: Washing

After cooking, the pulp contains dissolved lignin, spent lye, and degraded plant material. All of this must be washed out.

Process

1. Drain the cooking liquor (it can be reused for the next batch — it still has alkaline value)
2. Place the cooked fiber in a cloth bag or basket
3. Rinse under running water, or soak in several changes of clean water
4. Squeeze and agitate the pulp in each rinse
5. Continue until the rinse water runs clear and the pulp no longer feels slippery
6. Taste a tiny amount of the rinse water — it should be neutral, not soapy or bitter

Wash Thoroughly

Residual alkali in the pulp causes the finished paper to yellow and become brittle over time. The washing step is not optional — rinse until all traces of cooking chemicals are gone. Five to seven changes of water is typical.

Step 4: Beating

Beating is the mechanical process that transforms cooked fibers into papermaking pulp. It does two critical things: separates fiber bundles into individual fibers, and fibrillates (frays) the fiber surfaces to improve bonding.

Why Beating Matters

Unbeaten cooked fiber makes terrible paper — loose, porous, and weak. Beating fibrillates the fiber surfaces, creating tiny hairlike extensions that interlock and hydrogen-bond with adjacent fibers during drying. More beating produces stronger, denser, more translucent paper.

Hand Beating (Simplest)

1. Spread a handful of wet, washed fiber on a flat stone or wooden board
2. Pound with a wooden mallet or smooth stone
3. Turn and fold the fiber mass between blows
4. Continue for 15-30 minutes per handful
5. The fiber is ready when it has a porridge-like consistency and individual fibers are visible but very fine

Stamp Mill (Semi-Mechanized)

A stamp mill uses a waterwheel or foot-operated lever to lift and drop heavy wooden stamps into a trough of wet fiber.

Construction:

1. Carve a trough from a log — 30 cm wide, 40 cm long, 20 cm deep
2. Make heavy wooden stamps (5-10 kg) with flat or slightly convex faces
3. Mount on a pivot arm operated by foot lever or cam from a waterwheel
4. The stamps rise and fall into the trough, beating the fiber with each stroke

Hollander Beater (Advanced)

The most efficient beating device — a rotating cylinder with metal blades that shears fiber against a bedplate in a water-filled trough. Building one requires metalworking capability but dramatically speeds production.

Key components:

• An oval trough through which pulp circulates
• A roller with metal or hardwood blades
• A bedplate against which the roller shears
• The roller is turned by hand crank, waterwheel, or treadmill

Beating Assessment

Beating Level	Paper Characteristics	Test
Light (15-20 min hand)	Coarse, porous, opaque, weak	Fibers visible as strands in water
Medium (30-45 min hand)	Good strength, moderate opacity	Fibers are fine, water slightly cloudy
Heavy (60+ min hand)	Dense, translucent, very strong	Water is uniformly cloudy, no visible strands

The Jar Test

Drop a pinch of beaten pulp into a jar of water and shake. Hold up to light. If you see individual fiber strands floating, beat more. When the water looks uniformly cloudy with no visible strands, the pulp is well-beaten and ready for sheet forming.

Additives and Sizing

Internal Sizing

Sizing makes paper resistant to ink absorption (prevents ink from bleeding and feathering). Add sizing materials to the pulp before forming sheets:

• Rosin (tree resin) — Dissolve in hot alkali, add to pulp. The most effective internal size.
• Starch (from cooked rice, wheat, or potato) — Mix cooked starch into pulp at 2-5% by weight.
• Gelatin (from boiled animal bones and hides) — Add dissolved gelatin to pulp.

Fillers

Fillers improve opacity and smoothness:

• Kaolin (white clay) — 5-15% by weight makes paper whiter and smoother
• Chalk (ground calcium carbonate) — Whitens and buffers against acid
• Talc — Improves smoothness

Colorants

• Natural dyes — Add indigo, turmeric, berry juice, or other natural dyes to the pulp for colored paper
• Bleaching — Spread pulp on screens in direct sunlight for several days to whiten it. Alternatively, brief soaking in very dilute lye lightens the color.

Storing Pulp

Prepared pulp can be stored for weeks or months:

1. Drain excess water from beaten pulp
2. Press into blocks or balls
3. Store in a cool, dark place
4. Rewet and re-beat briefly before use
5. In warm weather, add a splash of vinegar to prevent mold growth

Common Mistakes

1. Skipping the cooking step — Uncooked wood and straw fibers still contain lignin. The resulting paper is weak, stiff, and yellows rapidly. Always cook fiber-heavy materials in alkaline solution.
2. Under-beating — The most common pulp preparation error. Under-beaten pulp makes weak, lumpy paper that falls apart. Beat until no individual fiber strands are visible in the water.
3. Inadequate washing — Residual cooking chemicals degrade paper over time. Rinse until the water is clear and neutral.
4. Too little water — Pulp should be beaten in plenty of water — a soupy consistency. Beating dry or thick pulp damages fibers by cutting rather than fibrillating them.
5. Inconsistent beating — Beat all the pulp evenly. Mixing well-beaten and under-beaten fiber produces sheets with inconsistent strength and texture.

Summary

Pulp Preparation — At a Glance

• Soak fiber 24-72 hours, cook in wood ash lye for 2-8 hours to dissolve lignin
• Wash in 5-7 changes of clean water until rinse water runs clear and neutral
• Beat the washed fiber until no individual strands are visible in water (the jar test)
• More beating produces stronger, denser, more translucent paper
• Add sizing (rosin, starch, or gelatin) to prevent ink bleeding
• Cotton rags need minimal cooking; wood chips need 6-8 hours
• Handle lye with care — caustic to skin and eyes
• Pulp can be stored as pressed blocks for months if kept cool