What happened
During a recent multi-year project involving a series of 17th-century legal manuscripts, conservators identified several recurring points of failure that necessitated a standardized treatment protocol. These failures were primarily located in the sewing structure and the substrate's chemical stability.
- Sewing failure:85% of the volumes exhibited broken linen threads and detached signatures.
- Acidic degradation:The paper components showed significant browning and brittleness due to high lignin content and acidic ink.
- Vellum distortion:The covers had contracted, preventing the books from closing and exposing the text block to dust and light.
Re-sewing Signatures onto Historical Cords
The foundation of a book's structure is its sewing. In the 17th century, books were typically sewn onto raised cords or alum-tawed thongs. Over time, these cords can snap under the tension of the heavy vellum covers. The restoration process requires the careful disassembly of the book block. Each signature (a group of folded pages) is cleaned and repaired before being re-sewn. Conservators use unbleached linen thread, which is traditionally treated with refined beeswax. The beeswax serves a dual purpose: it lubricates the thread, allowing it to pass through the sewing holes without tearing the paper, and it provides a protective barrier against moisture and environmental pollutants. The thread is passed around original or historically appropriate cords using a 'link stitch' or 'kettle stitch' at the head and tail of the spine, ensuring a strong and flexible support system.
The Science of Aqueous Deacidification
Before re-assembly, the paper signatures often require deacidification. This is a critical step in preserving the textual content of the 17th-century archive. As paper ages, it produces organic acids that catalyze the breakdown of cellulose chains. Aqueous deacidification involves immersing the paper in a buffered solution, such as calcium bicarbonate or magnesium bicarbonate. This process neutralizes existing acids and leaves an alkaline reserve—a 'chemical shield' that protects the paper from future acidification. However, this process must be monitored with extreme care. The conservator must ensure that the inks are not water-soluble and that the paper's physical structure can withstand immersion. In cases where aqueous treatment is too risky, non-aqueous sprays containing magnesium carbonylethyl ricinoleate are used as an alternative.
Mechanical Stabilization with Custom Book Presses
Once the signatures are re-sewn and the covers are stabilized, the entire volume must be kept under pressure to ensure it dries flat and maintains its shape. 17th-century vellum has a tendency to 'spring back' to its warped state if not properly restrained during the drying process. Conservators use custom-fabricated book presses with adjustable platens. These presses allow for the application of even pressure across the entire surface of the book. The use of 'interleaving'—placing sheets of acid-free blotting paper or polyester film between the pages—helps to draw out moisture in a controlled manner. This mechanical stabilization can take weeks or even months, as the vellum slowly acclimates to its restored shape and the adhesives fully cure.
The goal of structural restoration is to create a sympathetic repair that respects the original craftsmanship while ensuring the book survives for another four centuries.
Micro-Spatula and Bone Folder Precision
The final stages of restoration involve the meticulous detailing of the cover and joints. A micro-spatula is used to apply minute amounts of adhesive beneath delaminated layers of vellum, effectively 'knitting' the surface back together. This tool allows the conservator to reach into tight spaces without causing additional stress to the material. Following the adhesive application, a fine bone folder is used to smooth the surface and define the joints. The bone folder is essential for achieving a sharp, precise crease in the vellum, which is necessary for the book to open properly. Because bone is a natural material, it can be polished to a high degree of smoothness, ensuring that it does not scratch or abrade the historical substrate during use.
- Initial Assessment:Microscopic examination of fibers and ink stability.
- Disassembly:Careful removal of failed sewing and degraded glues.
- Stabilization:Chemical treatment of paper and physical repair of vellum.
- Reconstruction:Re-sewing signatures and re-attaching covers using archival methods.
