Analysis of efflorescence on surface of beeswax seals.

The aim of this study was to analyse the efflorescence developed on the surface of beeswaxes of different origin, age and storage history. In order to correlate the occurrence and the composition of the efflorescence with chemical changes of beeswax, the analyses of samples of historic and recent beeswaxes were proposed as well. Such an approach would enable the generalization of the results to considerable extent and provide a reliable basis for a further research, focused on explanation and prevention of this phenomenon. 

The mechanism behind the formation of this efflorescence is still a matter of discussion. Most often, it is considered to be a product of a physicochemical process, rather than of a chemical reaction. Various factors are suspected to promote its development: extreme temperatures, fluctuations in temperature, higher cooling rates during solidification, lower or higher relative humidity  the presence of impurities in the beeswax, degradation processes  and the presence of admixtures such as stearine or resins, to name a few.

Several authors have published the results of analyses of these crystals, which were collected from the surfaces of historical seals or various types of wax museum artifacts. However, almost all of these studies dealt with only a few samples, leaving uncertain the extent to which the generalization of their results is possible.

In some cases, aliphatic hydrocarbons naturally occurring in beeswax itself were identified as the main components of the “wax bloom”. Novotná specified these compounds as alkenes containing 31, 32, 33 and 35 carbon atoms. It was suggested that their migration to the surface could be promoted by the recrystallization of beeswax at lower temperatures, especially below a “critical” temperature interval of 12 to 16 °C . Similarly, Bacílek described the efflorescence process as an outflow of more volatile unsaturated compounds characterised by the melting point about 38 °C .

However, in other samples, almost exclusively fatty acids, especially palmitic and stearic acids, have been identified. These compounds can also be detected in pure beeswax. According to some experts, their higher content can be a consequence of the hydrolysis of wax esters during the natural ageing of beeswax or due to stearine admixtures.

Some authors have also reported the occurrence of efflorescence which consists mainly of beeswax itself, sometimes in combination with a small amount of water.

Considering the variability of these results, the question arises whether the composition of crystals from similar material can actually vary: for example, whether it depends on the storage conditions, or whether it is connected mainly with a content of specific admixtures. The primary aim of this study is to gain deeper insight on the differences between the chemical composition of various samples of efflorescence on beeswax seals, and to generalize these results within a selected field of interest.

Conclusions

The composition of the efflorescence layer was found to be similar in all of the samples, regardless of their origin, age and storage history. As main components, linear alkenes containing 31 and 33 carbon atoms, more precisely (Z)-hentriacont-10-ene and (Z)-tritriacont-10-ene, were identified. The other unsaturated compounds detected were various isomers of linear alkenes containing 31, 32, 34 and 35 carbon atoms. All samples contained also linear alkanes with a chain length of 23 to 33 carbon atoms.

It was confirmed, that all compounds identified in “wax bloom” naturally occur in recent Mid-European beeswax. However, the historical beeswaxes contained only traces of unsaturated hydrocarbons, if anything. The efflorescence was observed primarily on the surfaces of those samples, which contained larger proportion of alkenes.

The presented results have been used as a basis for a further research focused on the explanation and prevention of the described phenomenon. A new material based on modified beeswax, which should be resistant to “blooming”, has been prepared and the possibility of its use for conservation purposes is being studied at present.

Bartl, Benjamin, et al. "Analysis of efflorescence on surface of beeswax seals." Journal of Cultural Heritage 13.3 (2012): 275-284.

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