Sizing solution is a liquid coating that controls how absorbent a surface is, and making one at home is straightforward with a few common ingredients. The exact recipe depends on what you’re sizing: paper, fabric, or artist’s canvas each call for different formulas. Most sizing solutions fall into three categories: starch-based, gelatin or animal glue-based, and cellulose-based. Here’s how to make each one.
Starch-Based Sizing for Paper and Fabric
Starch sizing is one of the oldest methods, used since at least the 13th century when Italian papermakers brushed thick starch paste onto finished sheets. It works by filling in surface pores, making paper smoother and less ink-absorbent, or giving fabric a crisp, polished feel.
To make a basic wheat starch sizing solution, you’ll need wheat starch (or cornstarch as a substitute) and water. Mix 1 to 2 tablespoons of starch into a small amount of cold water first, stirring until you have a smooth, lump-free slurry. Then pour this mixture into about 2 cups of boiling water while stirring continuously. Keep stirring until the liquid thickens to a consistency somewhere between milk and thin gravy. For paper sizing, you want it thinner so it soaks in evenly. For fabric stiffening, a slightly thicker consistency gives more body.
Historical recipes sometimes combined equal parts chalk and starch for a heavier fill, useful for patching uneven surfaces. For most home projects, plain starch works fine. Let the solution cool to a warm, workable temperature before applying it with a wide brush or by dipping the material directly. Starch sizing is easy to wash out, which makes it a good choice for fabrics you’ll eventually launder.
Rabbit Skin Glue Sizing for Canvas
If you’re preparing a canvas for oil painting, rabbit skin glue is the traditional choice. It seals the canvas fibers and prevents oil paint from soaking through and eventually rotting the fabric. The standard ratio is 40 to 70 grams of rabbit skin glue per quart (roughly one liter) of water. Use the lower end for a more flexible size on canvas, and the higher end for rigid panels.
Start by sprinkling the dry glue granules into room-temperature water and letting them soak for several hours or overnight. The granules will absorb water and swell into a soft, jelly-like mass. Next, heat this mixture gently in a double boiler (a pot set inside a larger pot of simmering water). Never boil the glue directly, as high heat breaks down the proteins and weakens the bond. Stir until the granules dissolve completely into a smooth, warm liquid. The solution gels as it cools below roughly 120°F (49°C), so you need to apply it while still warm using a wide, flat brush. Work it into the weave of the canvas with firm strokes. One or two thin coats is typical, letting each coat dry fully before adding the next.
Rabbit skin glue sizing does have a downside: it reacts to humidity, swelling and shrinking as moisture levels change. This can cause cracking in paint layers over time. Some artists now prefer synthetic alternatives for this reason, but for traditional gesso preparation, rabbit skin glue remains the standard.
Gelatin Sizing
Food-grade gelatin from the grocery store makes a perfectly functional sizing solution for paper, bookbinding, and light fabric work. It’s essentially a refined version of the animal glues used for centuries.
A 5% to 10% solution covers most applications. For a 10% solution, dissolve 100 grams of gelatin in 900 grams (milliliters) of water. Sprinkle the gelatin over cold water and let it bloom for 10 to 15 minutes until it swells. Then heat the water gently, stirring until the gelatin dissolves completely. Avoid boiling. For paper sizing, a weaker 3% to 5% solution is usually enough to reduce ink bleed without making the sheet feel plasticky. For a stiffer result on fabric or heavier paper, go with the full 10%.
Apply gelatin sizing warm, either by brushing it on or by briefly dipping sheets into a shallow tray of the solution. It sets as it cools, so work in a warm room and keep the solution in a warm water bath while you’re using it.
Methyl Cellulose Sizing
Methyl cellulose is a plant-derived powder popular with bookbinders, paper conservators, and printmakers. It’s acid-free, doesn’t attract mold the way starch and gelatin can, and stays flexible when dry.
The mixing process is a bit counterintuitive. Dissolve 2 tablespoons of methyl cellulose powder in half a cup of boiling (or very hot) water. Stir thoroughly until all the granules absorb water and the mixture turns thick and syrupy. Then add 1 cup of very cold water and mix well. The cold water thins it to a workable consistency and helps it hydrate fully. You can adjust the thickness by adding more cold water for a thinner size or using less for a heavier coating.
Methyl cellulose is forgiving to work with. It doesn’t gel like gelatin, so you can take your time brushing it on. It’s also reversible with water, which is why conservators favor it for archival paper repair.
Choosing the Right Type
- For sewing and fabric stiffening: Starch sizing is inexpensive, washes out easily, and gives a clean, crisp hand to cotton and linen.
- For oil painting canvas: Rabbit skin glue or a synthetic alternative provides the strong barrier needed to protect fibers from oil penetration.
- For watercolor or printmaking paper: Gelatin sizing at 3% to 5% controls how much the paper absorbs, preventing colors from bleeding.
- For bookbinding or paper conservation: Methyl cellulose is archival-quality and won’t yellow or become brittle over time.
Preventing Mold and Spoilage
Any sizing solution made from organic ingredients (starch, gelatin, animal glue) will grow mold if stored at room temperature for more than a day or two. Make only what you need for a single session when possible. If you need to store leftovers, refrigerate them in a sealed container and use within a week. Gelatin and rabbit skin glue solutions can be reheated gently in a water bath for reuse.
For longer storage, a few drops of clove oil or lemongrass oil per cup of solution act as natural mold inhibitors. Some recipes call for a tiny amount of alum (aluminum sulfate), which also hardens the sizing and improves water resistance, particularly in gelatin-sized paper. Add alum sparingly, roughly half a teaspoon per liter, since too much makes paper acidic and brittle over time. Methyl cellulose doesn’t need preservatives since it’s synthetic and resists biological growth on its own.
Application and Drying Tips
How you dry sized material matters as much as the sizing itself. Paper and fabric both tend to cockle (ripple and warp) as sizing dries unevenly, because different areas shrink at different rates. Restraining the edges during drying largely prevents this. For paper, pin or tape the sheets to a flat board, or dry them under weight between blotting sheets. For fabric, stretch it on a frame or pin it taut.
Apply sizing in thin, even coats. Multiple light applications produce a more uniform result than one heavy coat. Let each layer dry completely before adding the next. A wide, soft brush (3 to 4 inches) works well for most projects, though dipping is faster when sizing many sheets of paper at once. Work quickly with gelatin and animal glue solutions, since they thicken as they cool. If your solution gels mid-application, rewarm it gently rather than trying to brush on a lumpy coat.