Smoothing
Part of Paper Making
Surface smoothing techniques for finished paper — burnishing, calendering, and hammering to produce a writing surface that accepts ink cleanly.
Why This Matters
Even well-formed, well-pressed, and properly sized paper may have a surface texture that makes fine writing difficult. The mold screen leaves a faint grid pattern. Drying against a felt creates a slightly rough texture. Individual fibers project slightly above the sheet surface. On such a surface, a quill pen or reed catches and skips, drawing thick and thin lines erratically. Fine script becomes illegible; precision drawings develop ragged lines.
Smoothing compresses and aligns these surface irregularities, producing a paper surface that the writing instrument glides across cleanly and predictably. It is the final step in producing quality writing paper — the equivalent of planing a rough-sawn board before painting it. Without smoothing, paper is functional for rough notes and drafts. With smoothing, it becomes suitable for permanent records, careful correspondence, technical drawings, and printed books.
Smoothing also increases paper density and strength, as the compression process creates additional fiber-to-fiber bonds across the surface. A smoothed sheet is noticeably stronger in both tensile and tear tests than an unsmoothed sheet of the same paper. For documents that will be handled frequently — account books, maps consulted repeatedly, bound books — this added durability compounds the value of the smoothing step.
What Smoothing Does at the Microscopic Level
Freshly dried paper, even after pressing, has a three-dimensional surface. Fibers cross at different heights. Some fiber ends project slightly above the average surface plane. The screen texture of the mold creates a regular pattern of slight ridges and valleys. In transmitted light, these irregularities show as subtle variations in sheet translucency.
Smoothing applies compressive force to the surface, pressing protruding fibers flat and filling in the valleys with displaced fiber. The result is a surface where fiber heights vary much less from point to point — a flatter plane at the microscopic level.
Sized paper smooths better than unsized paper because the gelatin or starch creates a slightly plastic surface that deforms under pressure and retains the compressed shape when pressure is released. This is why smoothing is typically done after sizing, not before.
Tool 1: Burnishing Stone
The burnishing stone is the simplest smoothing tool: a smooth, dense, polished stone used to rub the paper surface under firm pressure.
Stone selection: The ideal burnishing stone fits comfortably in the hand, has a naturally smooth, polished surface, and is dense enough to stay cool while rubbing (heavy contact pressure generates slight heat from friction). Agate, flint, quartz, jasper, and similar hard, fine-grained stones work well. Rounded river stones of the right size and smoothness are available in most streams.
The stone should have no sharp edges or surface irregularities — run your finger over it and you should feel no catches or rough patches. Any irregularity will transfer to the paper as a scratch.
Burnishing technique:
- Lay the sized, dried sheet on a smooth, hard surface (a flat stone slab, a planed wooden board). The backing surface should also be smooth — surface texture underneath transfers through the paper to the burnishing.
- Hold the stone firmly and apply steady downward pressure while moving it in long, overlapping strokes.
- Work first in one direction (say, top to bottom), covering the entire sheet. Then work in the perpendicular direction (left to right). This cross-grain approach ensures even treatment.
- Apply moderate to heavy pressure. You should feel slight resistance as the stone compresses fibers — not sliding frictionlessly, but not dragging or catching either.
- Three to four passes in each direction is typically sufficient for writing paper. Increase passes for paper requiring maximum smoothness.
Signs of good burnishing: The surface develops a faint sheen — not a high gloss, but a subtle visual smoothness compared to unburnished areas. Run your fingernail across the surface — a burnished area should produce a slightly different sound (higher pitch) than an unburnished area.
Rate: An experienced burnisher can process approximately 20 to 30 sheets per hour. This is slow for large-scale production but adequate for small community needs.
Tool 2: Polished Bone or Ivory Burnisher
Before polished stone, many papermakers used flat, polished bone tools — the same instruments bookbinders use to crease and fold paper. A flat cattle rib bone, sanded and polished on both faces, makes an effective burnisher for smaller sheets.
The advantage over stone is lighter weight (less fatigue for the operator) and more precise edge control for burnishing specific areas of a sheet. The disadvantage is that bone is softer than stone and will eventually develop micro-scratches that transfer to paper — requires periodic re-polishing.
A knapping or bone-working craftsperson in your community can produce multiple burnishing tools from a single cattle carcass.
Tool 3: Hammer Calendering
For larger-scale production, individual burnishing becomes a bottleneck. Hammer calendering processes multiple sheets simultaneously:
- Collect 10 to 20 sized, dry sheets.
- Stack them between two smooth, flat boards (hardwood, planed completely flat).
- Strike the top board firmly and evenly with a wooden or stone mallet. Apply blows in a regular pattern — move across the board in rows, spacing blows 3 to 5 cm apart.
- After covering the full surface, turn the stack 90 degrees and repeat.
- Remove sheets, separate, and check for sticking (the impact may have caused adjacent sheets to bond slightly along the stack edges — peel gently).
This method is faster than individual burnishing (one set of hammering processes 10 to 20 sheets in a few minutes) but produces less consistent results — sheets at the edge of the stack may be treated differently than those in the center, and local pressure variation from hammer blows creates slight texture variations.
Improve consistency by using a flat, heavy stone slab as the top pressing element instead of a board, and a mechanical press instead of a hammer — apply press pressure gradually rather than impact.
Tool 4: Roller Calendering (Intermediate Scale)
A simple roller calendar passes paper between two smooth, heavy cylindrical rollers, applying even compressive pressure across the full sheet width. This is more consistent than hammer calendering and faster than individual burnishing.
Construction: Two hardwood cylinders, 8 to 12 cm diameter, 50 to 60 cm long. The wood must be very dense and straight-grained — maple, boxwood, lignum vitae, or similar close-grained hardwood. Carve each cylinder as round as possible, sand progressively to smooth finish.
The rollers are mounted in a simple frame with bearings (smoothed wooden or stone sockets) at each end. They should be parallel and in contact along their full length. A gap-adjustment mechanism (wedges at the bearing sockets) allows controlling the nip pressure.
Operation: Feed sheets one at a time between the rollers while turning the rollers (via handles attached to roller ends). The sheet passes through the nip and emerges on the other side with a uniform surface compression.
Maintenance: Rollers must remain clean — any paper fiber or size residue accumulation creates surface irregularities. Wipe clean with a damp cloth between sessions. Re-smooth with fine abrasive (sandstone, then progressively finer stones) if surface irregularities develop.
Smoothing Different Paper Types
Writing paper (for quill, reed pen, or brush): Light to moderate burnishing. The surface should be smooth but retain slight tooth — completely smooth paper can be too slippery for comfortable writing with some tools. Test: the writing instrument should glide without catching but not slide uncontrolled.
Printing paper (for woodblock or other impression printing): Moderate burnishing. A smooth surface takes impression cleanly. However, over-smoothed paper may not hold ink in hollows of a relief print — some surface texture improves ink retention.
Drawing paper (for charcoal, chalk, pencil): Light burnishing or none at all. Drawing media require surface tooth to adhere. Heavily burnished or very smooth paper sheds charcoal and graphite. However, pen-and-ink drawing requires smooth surface — know the intended use before smoothing drawing paper.
Archival records: Maximum burnishing. The densest, most consolidated surface provides the best barrier against moisture penetration, insect damage, and mechanical abrasion over centuries.
Troubleshooting Surface Problems
Surface has parallel lines (mold texture visible): Not enough burnishing. The mold screen pattern requires 5 to 6 passes with a burnishing stone to fully smooth away. Alternatively, a brief dampening (breathe on the surface or pass briefly through steam) and immediate burnishing makes the fibers more pliable and removes the pattern more easily.
Surface has shiny irregular patches: Uneven size application before burnishing. Some areas were heavily sized (now shiny), others less so. Re-size evenly, allow to dry, re-burnish.
Paper surface scratched by burnishing stone: Stone has surface irregularities. Sand the stone with progressively finer abrasive to restore smooth surface. Check the backing surface as well — a scratch in the backing board will telegraph through the paper.
Sheets sticking together after hammer calendering: Too much moisture in the sheets before calendering. Ensure sheets are bone dry before calendering. If sticking occurs, peel sheets apart carefully; the bond is usually weak enough that careful peeling produces a clean separation. Re-dry and re-calender.
Paper stiff and boardlike after sizing and burnishing: Over-sized (too much gelatin or starch). The size layer is too thick and has hardened the sheet. For a light paper, this is acceptable — some rigidity aids ink application. For paper that needs to fold or be bound, the stiffness is a problem: reduce size concentration in the next batch.
Smoothing is the final craft step in papermaking. It requires no special equipment beyond a good stone, and the time investment is returned many times over in the usability of the finished product. A community that takes paper making seriously enough to smooth every sheet is a community that understands what permanent records are worth.