The structural restoration of 17th-century books requires a profound understanding of the mechanical forces acting upon the text block and its binding. Over centuries, the original sewing supports—often made of vegetable fibers or alum-tanned leather—undergo significant degradation. The animal glues used to coat the spines become brittle, leading to the cracking of the spine and the detachment of signatures. Restoration protocols focus on the re-establishment of these mechanical connections using historically appropriate materials and modern engineering principles.
Traditional hide glues and parchment pastes, while historically accurate, present specific degradation pathways. As these protein-based adhesives age, they lose their plasticizers and become acidic, which can lead to the "burning" of the paper at the hinge. Modern conservators must carefully remove these degraded adhesives using mechanical means, such as scraping with micro-spatulas, or through the application of localized moisture via poultices to soften the glue for safe removal.
What changed
Historically, book restoration often involved "over-restoration," where original bindings were discarded in favor of modern, tight-back structures. This led to the loss of significant historical evidence regarding 17th-century binding practices. Today, the philosophy has shifted toward minimal intervention and structural stabilization. The focus is no longer just on making the book look new, but on preserving the "archeology" of the book. This includes keeping original sewing holes, reusing original boards when possible, and employing reversible adhesives like wheat starch paste or methyl cellulose instead of permanent synthetic glues.
Re-sewing Protocols and Thread Treatment
Once the text block has been cleaned and the signatures have been reinforced with Klucel G or Japanese tissue, the re-sewing process begins. This is a critical phase in restoring the book’s functionality. 17th-century books were typically sewn onto raised cords or recessed bands. Conservators replicate this by selecting high-quality linen thread that matches the weight and twist of the original material.
- Thread Preparation:The linen thread is passed through a block of refined beeswax. This coats the fibers, reducing internal friction and preventing the thread from tangling or cutting through fragile paper signatures.
- Support Alignment:New cords are aligned with the original sewing stations (holes) to avoid creating new points of stress in the paper.
- Tension Management:The book is placed on a sewing frame, which keeps the supports under uniform tension. The conservator sews each signature individually, ensuring a consistent link-stitch that allows the book to open flat without straining the spine.
Adhesives and Spine Consolidation
The choice of adhesive for spine consolidation is critical. Traditional hide glue is a collagen-based adhesive derived from animal connective tissues. While it provides a strong bond, its brittleness over time is a known failure point. In modern conservation, purified wheat starch paste is often preferred for its longevity and total reversibility. For applications requiring more flexibility, a mixture of starch paste and a synthetic polymer like ethylene vinyl acetate (EVA) may be used, though this is less common in high-level conservation of 17th-century artifacts.
The objective of spine lining is to provide support to the text block while allowing for the necessary flexibility to accommodate the movement of the vellum cover, which expands and contracts with atmospheric changes.
The lining materials—usually layers of Japanese paper or fine linen—are applied to the spine to distribute the stresses of opening and closing. This prevents the concentration of force on the sewing threads, thereby extending the life of the repair.
Evaluation of Historical Inks and Pigments
The chemical profile of 17th-century inks, particularly iron gall ink, must be considered during any structural repair. Iron gall ink contains iron(II) sulfate, which can undergo oxidation to form iron(III) ions and sulfuric acid. This process, known as ink gall, leads to the perforation of the paper. When re-sewing or consolidating signatures, the conservator must ensure that any moisture introduced does not trigger the migration of these acidic ions.
Comparative Analysis of Binding Supports
| Support Material | Historical Period | Durability Profile | Conservation Recommendation |
|---|---|---|---|
| Hemp/Linen Cords | 16th-18th Century | High tensile strength; prone to acidic rot | Replace with unbleached linen thread |
| Alum-Tanned Leather | 15th-17th Century | Extremely durable; resistant to acid | Retain if intact; supplement with linen if failed |
| Parchment Slips | 17th Century | High stiffness; can become brittle | Reinforce with new parchment or Japanese tissue |
By analyzing these materials, conservators can tailor their approach to the specific needs of the volume, ensuring that the mechanical repairs do not introduce new chemical vulnerabilities. The result is a stabilized artifact that retains its historical context while regaining the structural integrity necessary for scholarly consultation.
