Paper Finishing

Part of Paper Making

Final treatments applied to dried paper — sizing, calendering, and surface treatments that improve writing quality, durability, and appearance.

Why This Matters

Raw dried paper is useful for some purposes but falls short for others. Unsized paper absorbs ink immediately and spreads it sideways — a phenomenon called “feathering” — making precise writing impossible and causing fine lines to bleed into fuzzy edges. Rough paper surface makes ink application uneven. Paper made from reactive plant materials may be acidic and will yellow and become brittle within decades.

Finishing addresses all of these problems. Sized paper accepts ink without feathering. Calendered (smoothed) paper provides a consistent surface for fine writing and drawing. Properly treated paper lasts centuries — the reason we can still read documents from medieval Europe and ancient China is that those papermakers understood finishing.

For a rebuilding community, paper finishing is what separates functional record-keeping from a frustrating process that wastes expensive ink and produces illegible documents. If your community is investing effort in producing paper, investing additional effort in finishing it properly makes every subsequent use of that paper more effective.

Sizing: The Most Important Finishing Step

Sizing adds a substance to paper that fills the pores between fibers, creating a surface barrier that prevents ink from wicking deeply into the sheet. Sized paper allows ink to sit on or just below the surface, where it dries in place without spreading.

Animal Glue Size (Traditional Western Method)

Animal glue size — made from hide, bone, or hoof — is the traditional sizing for European writing paper and produces excellent results. The gelatin in animal glue fills fiber pores and creates a firm, consistent surface.

Preparation: Make a stock solution by soaking dried animal glue (or fresh scraps of skin and connective tissue) in cold water for several hours, then heating gently until dissolved. Do not boil — boiling degrades gelatin and produces a weaker size. Target concentration: 2 to 4 percent gelatin by weight (2 to 4 grams of dry glue per 100 ml of water). The solution should be liquid at 60°C and gel at room temperature.

Application — dipping method: Heat the size solution to 40 to 50°C, keeping it liquid. Hold dried paper sheets by one corner and dip them fully into the warm size, ensuring complete coverage. Hold briefly to allow size to penetrate (5 to 10 seconds), then remove and hang to dry. Sheets are usually dipped individually and hung on rope or racks.

Application — brush method: For large sheets or when a dipping vat is not available, brush warm size onto both surfaces of the sheet with a broad, soft brush. Work quickly and evenly — size gels fast on cold paper. Brush once in each direction (horizontal then vertical) to ensure even coverage.

Drying after sizing: Hang sized sheets in a warm, well-ventilated space. They will feel stiff and slightly shiny when dry. Allow to dry completely before use — partially dried sized paper tears easily.

Testing: Write a test line with your ink on a small scrap. If ink absorbs without spreading, sizing is adequate. If ink feathers, the size concentration is too low or penetration was insufficient. If ink beads on the surface, size is too heavy — dilute and retry.

Starch Size (Alternative Western / Traditional Eastern Method)

Cooked starch makes an effective size that is easier to produce than animal glue. Wheat starch, rice starch, or potato starch all work well.

Preparation: Mix starch powder with cold water (approximately 5 percent concentration). Heat while stirring constantly until the mixture thickens and becomes translucent — this is gelatinization, where starch granules burst and form a gel. Thin with additional water to the consistency of thin cream. Strain through fine cloth to remove lumps.

Application: Brush onto one or both surfaces of dried paper sheets while warm. Work quickly. Allow to dry completely. Unlike animal glue size, starch size does not need to be kept warm during application, though warm starch spreads more easily than cold.

Results: Starch size works well for calligraphy inks and writing brushes. It is slightly less effective than animal glue for quill or pen writing with liquid iron gall ink, as starch is somewhat more absorbent than gelatin. Japanese and Chinese papermakers traditionally used starch size with excellent results.

Alum-Rosin Size (Modern Equivalent)

If pine rosin is available, an alum-rosin size works well. Dissolve rosin in hot water with a small amount of soda ash or wood ash lye, then add alum (potassium aluminum sulfate, available from mineral sources or dye-fixing processes). The alum precipitates rosin onto the fiber surfaces.

This method sizes paper during or just after sheet formation rather than after drying — the size is added directly to the pulp vat. Every sheet pulled from the size-laden vat is uniformly treated. However, alum-rosin sizing is acidic and causes paper to deteriorate faster over decades than neutral-pH sizing. For archival documents, prefer animal glue or starch size.

Calendering and Surface Smoothing

Calendering compresses paper fiber under pressure to create a smoother writing surface. Even well-formed, sized paper has microscopic surface irregularities from the screen texture of the mold. Calendering reduces these irregularities.

Stone Burnishing (Simplest Method)

Rub the sized, dried sheet repeatedly with a smooth, polished stone — agate, quartz, or any dense smooth river stone works. Apply firm, even pressure in long strokes in one direction, then the perpendicular direction. The stone compresses surface fibers and fills in microscopic depressions.

This is the simplest and most widely available method, though it is slow. A skilled burnisher can process 10 to 20 sheets per hour. The result is noticeably smoother than unburnished paper — suitable for fine pen work and detailed drawing.

Hammer Calendering

Stack dry, sized sheets between flat wooden boards and hammer the stack firmly with a wooden mallet. The impact compresses all sheets simultaneously. More efficient than individual burnishing for bulk production.

After hammering, separate sheets and check for sticking (sheets may bond slightly — peel apart gently). Lightly dampening sheets before hammering and using boards with a very smooth surface improves results.

Post-Press Calendering

After the final pressing (which uses felt-padded surfaces), pass sheets through a simple calendar — two heavy, smooth rollers, one above the other, with the sheet fed between them. The rollers press the sheet flat and smooth with even, continuous pressure. This is the most effective method for large-scale production.

Building wooden rollers requires a lathe or careful hand-shaping of a hardwood cylinder. The rollers must be perfectly round and smooth — any surface defect transfers to every sheet passing through.

Surface Treatments for Specific Uses

Map Paper

Maps require paper that does not expand or contract significantly with humidity changes — dimensional stability prevents map distortion. After standard sizing, brush one side with dilute paste (starch or animal glue) and allow to dry under tension. This creates a slightly stiff surface that resists humidity-driven movement.

For permanent maps, consider sizing with a mixture of gelatin and a small amount of alum (slightly acidic, but increases water resistance significantly). Laminate particularly important maps by pasting two sheets together, cross-grained if possible (orient fibers at 90 degrees to each other), to reduce warping.

Tracing and Drawing Paper

Thin paper made semi-transparent for tracing requires a heavy oil treatment. After drying and sizing, brush linseed oil (or any drying oil) thinly onto both surfaces. Allow to cure for one to two weeks. The oil fills fiber pores and makes the paper translucent. Oiled paper is water-resistant but cannot be written on with water-based inks — use charcoal, graphite, or oil-based inks only.

Waterproof Paper

For paper used in wet conditions (labels on storage jars, outdoor signs, receipts handled in rain), a heavy wax treatment provides waterproofing. Melt beeswax and brush over both surfaces of dried, sized paper. Buff with a warm stone while wax is still soft. The resulting paper is somewhat stiff and cannot be written on after waxing — stamp or mark before waxing.

Writing Paper for Iron Gall Ink

Iron gall ink (made from tannin-rich plant galls and iron sulfate — see writing ink articles) is slightly acidic and corrosive. Paper intended for permanent records written in iron gall ink should be sized with alkaline or neutral sizing rather than acidic alum-rosin size. Calcium carbonate added to the pulp or applied as a light chalk layer provides an alkaline buffer that neutralizes any iron gall acidity over time, extending document life.

Quality Assessment

Before distributing finished paper to your community, assess each batch:

Writing test: Write several lines with the primary inks your community uses. Check for feathering (ink spreading sideways), bleed-through (ink visible on the reverse), and uneven absorption (ink looks different in different areas).

Strength test: Tear a small corner strip. Good writing paper should tear with moderate resistance in either direction. Paper that tears very easily has weak fiber bonding (under-beaten or under-pressed). Paper that tears with a ragged, branching tear line has long, well-beaten fiber — this is a good sign.

Surface test: Run a fingernail lightly across the surface. A properly sized and smoothed surface should feel faintly resistant — not rough, not slippery. A squeaky resistance indicates good gelatin sizing.

Aging test: Store a test sheet near a candle or in direct sunlight for a week. Compare color to a stored sheet. Rapid yellowing indicates acidic content in the fiber or size — investigate the pulp source and cooking method.

Finished paper that passes these tests is ready for the most important uses in your community: preserving knowledge, recording decisions, transmitting information across distance and time.