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Chapter 11 - Purfling and Binding

Authors' commentary and additional suggestions

What is Vulcanized Fiber?

 

It is a dense, hard, durable composite material made entirely of natural cellulose (typically cotton rags or wood pulp). It earned the name "vulcanized" historically because the chemical transformation mimics rubber vulcanization — taking a soft, pliable material and chemically cross-linking it into a tough, rigid state.

How Vulcanized Fiber is Made

  1. Pulp Preparation: High-purity cellulose paper sheets (cotton rag or wood fiber) are passed through a bath of zinc chloride (ZnCl2​) solution.

  2. Gelatinization: The zinc chloride partially dissolves and swells the surface of the cellulose fibers, turning them into a gelatinous mass.

  3. Lamination & Bonding: Multiple layers are pressed together. The swollen cellulose fibers cross-link directly to each other on a molecular level.

  4. Leaching & Drying: The zinc chloride is completely washed out with water, and the material is dried and calendered (pressed under heavy rollers).

The result is a homogenous sheet of pure cellulose with no artificial resins, glues, or binders.

 

Key Properties & Common Applications

  • High Mechanical & Tensile Strength: Surprisingly tough, lightweight, and resistant to tearing or splitting.

  • Electrical Insulation: Excellent dielectric strength, historically making it a staple material for electrical terminal boards, transformer insulation, and arc chutes.

  • Machinability: It can be machined, punched, stamped, sanded, and bent when moist.

  • Common Uses:

    • Abrasive sanding disc backings.

    • Structural shims, washers, and gaskets.

    • Flat top and bottom flatwork for electric guitar pickups.

    • Vintage luggage, trunk corners, and knife handle liners.

Plastic bindings

1. ABS (Acrylonitrile Butadiene Styrene)

  • Status: The standard for most modern factory and custom guitars.

  • Characteristics: Extremely durable, impact-resistant, stable, and cheap. ABS doesn't shrink, warp, or off-gas over time.

  • Working Properties: Glues easily using acetone or dedicated solvent cements (like Weld-On 16 or glue made by dissolving scrap ABS in acetone).

2. Celluloid (Cellulose Nitrate)

  • Status: The classic vintage material used by Martin, Gibson, and European makers from the late 19th century through the mid-20th century.

  • Types: Commonly used for decorative patterns like grained ivoroid, tortoiseshell, mother-of-pearl (pearloid), and plain white/black.

  • Characteristics: Made from plant cellulose treated with nitric acid and camphor. It has a distinctive organic depth and grain pattern that synthetic plastics can't quite replicate.

  • Drawbacks: Highly flammable and prone to aging ("celluloid rot"). Over decades, it off-gasses nitric acid, causing the plastic to shrink, crumble, and corrode nearby metal frets and hardware.

3. CAB (Cellulose Acetate Butyrate) & Cellulose Acetate

  • Status: Developed as a safer, more stable alternative to cellulose nitrate.

  • Characteristics: Captures the warm look and feel of vintage celluloid without the extreme flammability or chemical degradation. Many modern reproduction vintage bindings (like tortoiseshell and ivoroid) are made from CAB or acetate polymers.

4. PVC (Polyvinyl Chloride)

  • Status: Used occasionally on lower-cost mass-produced instruments.

  • Characteristics: Flexible and easy to bend around tight body radii without heat, but harder to solvent-weld cleanly compared to ABS or celluloid.

How Choice of Plastic Affects Lutherie Work

PropertyCelluloid (Nitrate)ABS

Solvent WeldingDissolves instantly in pure acetone for invisible, seamless purfling seams.Melts cleanly with acetone or ABS slurry.

Heat BendingSoftens quickly with heat, but requires care due to low flashpoint.Requires higher heat, holds shape reliably once cooled.

LongevityShrinks, turns brittle, and off-gasses over 40–70 years.Dimensionally stable indefinitely.

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