Dalia Jonynaitė et al: Mysteries of 'cera di Spagna': Investigation of historical wax seals in 16th-19th-century Lithuanian collections.

The different kinds of wax seals are common as a feature of archival manuscripts. Beeswax or resin (so-called cera di spagna) seals applied on the paper and paper-covered paste seals usually become vulnerable, fractured, crumbled or broken with the time. For better understanding of the secrets of cera di spagna used in the Lithuanian and Russian State Chancery, historical wax seals collections from 16-19th centuries taken from historical collections of the Vilnius University Library, the Wroblewski Library of the Lithuanian Academy of Sciences and Institute of Ancient Manuscripts Matenadaran (Yerevan, Armenia) have been investigated in order to determinate the binders and pigments or fillers. The organic binders in the samples were identified by ATR-FTIR spectroscopic technique; the pigments or fillers were detected by microchemical and SEM-EDX microanalysis methods. Beeswax binders were dominated in the collection from 16th century, whereas the beeswax-resin and resins mixtures compositions were detected in the collections from the later 17-19th centuries.

Considering the recipes of the historical wax seals compositions, wax seals samples from beeswax, beeswax–resin and resins mixtures compositions were prepared. The conservation compositions were made from beeswax-dammar mixtures in various ratios. Pure samples and samples on the paper were tested in accelerated ageing conditions using cycling of relative humidity from 90 %rh to 60 %rh and temperature from 38 oC to 20 oC in the moisture chamber for 4 weeks. Changes of the samples after accelerated ageing were evaluated by ATR-FTIR spectroscopy, by measuring pH, hygroscopicity and mechanical properties of the pure samples. The most significant changes in FTIR spectra and hygroscopicity values were detected in the resin mixtures, particularly, in shellac with rosin and Venice turpentine.

Authors:

Dalia Jonynaitė, Lithuanian Art Museum P. Gudynas Restoration Centre, Gintarė Latvytė, Daina Ragauskienė, Vilnius University