Surface Crystallisation on Beeswax Seals
by P. NOVOTNÁ & J. DERNOVŠKOVA
INTRODUCTION
Beeswax is regarded as one of the most stable natural materials'. However, a whitish bloom or even
a white layer, sometimes incorrectly regarded as mould, has been reported on seals made of pure
beeswax2,3. "Physical change through loss of small amounts of volatile material" 2 has been
suggested as a possible reason, whereas surface oxidation has been proved to take place3, based on
the FTIR identification of beeswax oxidation products. Producers of candles described a similar
phenomenon. They assigned low temperature as a reason for crystallisation and advise warming
candles in air in order to remove the whitish layer. Most authors discussing this problem4 refer to an
article5, which gives an explanation of the surface crystallisation based on polymorphic changes of
the wax or fat components.
Surface crystallisation of a mixture prepared from stearin wax, beeswax, ceresin or paraffin wax
and pine resin have been studied4 and palmitic and stearic acids identified as major components of
the crystalline layer using FTIR and MS techniques. An hypothesis explaining the crystal formation
has been described. Temperature fluctuations (evidence of a fire attack) were assumed to be the
cause of polymorphic changes in the wax mixture with a subsequent migration and crystallisation of
free fatty acids. The migration of free fatty acids was based on their function as plasticisers in the
mixture. Surface crystallisation has also affected seals in the so-called Archive of the Czech Crown
(ACK) in the State Central Archives of the Czech Republic in Prague. This archive contains the
most important and precious documents of the Czech state dating from 1158 to 1935 and its unique
character explains the increased attention paid to the stability of seals within it.
White crystals have occurred on the surface of 515 seals, about 31%, stored in the Depository I (see
Figs.l and 2). The crystals were apparent on both historic seals and on repaired areas using modern
beeswax. The degree of crystallisation and the size of the crystals were variable. Conditions in the
Depository were typi-
cally a relative humidity of 54-57% and a constant temperature of 12°C. Surprisingly, the effect was
much more pronounced on seals that had been surfaced cleaned whereas seals treated with propolis
("bee glue") on the surface did not show a significant crystallisation. The absence of crystallisation
was also observed on seals prepared from a mixture of beeswax with inorganic pigments. As no detailed study of this phenomenon occurring on pure beeswax has been reported until now, it was
difficult to estimate possible risks to the seals. In our study we aimed to determine the chemical
composition of the crystalline layer using modern analytical methods, to test the influence of
different factors on the crystal formation using model seals, to explain this phenomenon on a
molecular basis and, subsequently, to assess the harmful effect of crystallisation to seals. An understanding of the whole process was expected to help determine conditions suitable for the storage of
both historic documents and their beeswax seals.
EXPERIMENTAL
Materials
• Chemicals: Chloroform of p.a. purity (Lachema, Prague), virgin beeswax representing freshly
produced wax (Bee Research Institute at Dol, Libcice nad Vltavou, Czech Republic)
• Samples: A crystalline layer or a whitish bloom was scraped off the surface of seven seals made
of pure beeswax, all belonging to the Archive of the Czech Crown (ACK). Four samples were taken
from original historic wax (ACK 1548 - 17.3.1437, Prague, emperor Zikmund; AČK 622 8.11.1357, Prague, Fridrich from Bibrstejn; ACK 2321 - 24.9.1618, Prague, Vaclav Redelfester
from Wildersdorf; ACK 2123 - 19.11.1546, Vienna, king Ferdinand I) and three samples from
modern beeswax (ŘF52- 18.6.1473, Vienna, cardinal Marek; AČK 1590 - 6.5.1454, Prague, king
Ladislav; ŘDO46 - 25.7.1511, Budm, Vladislav II, king of Bohemia and Hungary) used for
replacing missing parts of the seal. Seals were not stored in contact with the parchment or paper
document.
• Model seals: Seal castings were prepared from molten mass virgin beeswax heated to 80°, 90°,
100° and 150°C (C80-C150). Other model seals were formed from wax heated in water (W) and by
hands during kneading (H). Propolis was applied on the surface of seal castings made of molten
mass heated to 90 °C
(P90).
Fig. 3. Chromatogram of a sample AČK1590. Peaks no. 1-3 belong to n-alkanes with 25, 27 and 29
carbon atoms, peaks no. 4-7 to alkenes with 31, 32, 33 and 35 carbon atoms and peaks no.8-12 to
saturated monoesters with 40-50 carbon atoms.
Chemical analyses of the surface crystals
Gas-chromatographic (GC) analysis without preceding sample derivatization has often been used
for the analysis of waxy materials6, 7, 8. The GC technique was therefore employed for the
characterization of the crystalline surface layer, taking advantage of mass spectrometric detection
and identification of unknown compounds. However, the sample amount eluting from the column is
strictly dependent upon the volatility and polarity of the components. In order to test the presence of
polar and macromolecular compounds, additional measurements were performed.
Technical details are given in the annexe.
GC and GC/MS analysis
Seven samples were analysed using the GC technique with FID detection and chromatograms of a
similar character were observed, irrespective of the age of the beeswax substrate. A record obtained
after the analysis of the sample AČK 1590 can be seen in Fig. 3.
Fig. 4. Chromatogram of beeswax. Peaks no.1-6 belong to n-alkanes with 21, 23, 25, 27, 29 and 31
carbon atoms, peaks no.7 and 8 to alkenes with 31 and 33 carbon atoms, peaks no.9-14 to saturated
monoesters with 40, 42, 44, 46, 48 and 50 carbon atoms and peaks no. 7-7 to saturated fatty acids
with 22, 24, 26, 28, 30, 32 and 34 carbon atoms.
An identification of peaks was carried out using the literature data6, 9 and GC/ MS measurements.
The same compounds were identified in chromatograms of crystalline samples as in the
chromatogram of pure beeswax (Fig. 4). Substantially higher amounts of alkenes with 31, 32, 33
and 35 carbon atoms represented the major difference between crystalline samples and beeswax. A
sum of peak areas of these alkanes represented 42.8-91.1% (GC-FID measurements) with an
average amount of 78.5%, whereas in beeswax itself only 5.5% of alkenes were detected. The
amount of alkenes is therefore approximately 15 times higher in crystalline samples than in
beeswax.
Taking into account the limited elution of polar compounds under these conditions, derivatized
samples were prepared prior to GC analysis. Acetanhydride (hydroxyl group derivatization) and
diazomethane (carboxyl group derivati-zation) were used according to the procedure described by
Lawrence et al.10. No additional peaks were observed in chromatograms of derivatized samples. It
can be concluded therefore that the surface crystals do not contain very polar compounds, e.g., fatty
acids or higher alcohols in concentrations above their detection limits.
Fig. 5: Mass spectrum of a sample AČK 1590. Masses of m/z = 434, 462 and 490 correspond to
alkenes C31H62, C33H66 and C35H70, respectively. Masses of m/z = 592-816 belong to saturated
monoesters with an even number of carbon atoms C40H80O2 - C56H112O2. Mass peaks in the range of
m/z = 50 - 420 belong to fragment ions of hydrocarbon chains and the mass of m/z = 257 to a
fragment ion of esters (palmitic acid ion).
DTMS analysis
DTMS measurements were performed in order to test the presence of high-molecular components
in the samples. They could be detected in the mass spectrum as pyrolysis product ions of nonvolatile molecules. The mass spectrum obtained for a sample AČK 1590 can be seen in Fig.5.
Compounds identified in crystalline samples using GC and GC/MS techniques were also found by
DTMS measurements. Peaks of alkenes C31H62 and C33H66 dominated in the spectrum. No ions of
pyrolysis products, possibly belonging to macromolecular components, were observed.
The crystalline layer showed the following characteristics:
• appearance: white crystals of a variable size;
• solubility: good in chloroform and benzene;
• composition: 42.3-91.1% of alkenes with 31, 32, 33 and 35 carbon atoms and 57.7-8.9% of other
components of beeswax (alkanes, esters);
Table 1. Intensity of beeswax crystallisation tested on model seals. The crystallisation was observed on seals stored for 6 months under specific climatic conditions.
*
castings made from molten mass heated to 80, 100 and 150°C resp.
** castings made from molten mass heated to 90°C and treated with propolis
+ seals formed by kneading of beeswax
++ seals made from wax heated under water
• melting point of the whole sample: 34-35°C;
• melting point of alkenes isolated by preparative TLC: 34-35°C.
Testing of factors influencing the crystal growth
Model seals were prepared in order to test the influence of different factors on the surface
crystallisation. The following factors were studied based on previous indications of their
significance:
• beeswax processing during preparation of a seal,
• physical conditions of storage (temperature, humidity),
• surface treatment with propolis as a consolidation material11.
As no oxidation products of beeswax were identified in the surface layer, the influence of oxidation
reactions on crystal formation reported by Robbins et al.3 was not tested. Model seals were exposed
to conditions specified in Table 1. After a period of six months the intensity of the surface
crystallisation on the model seals was examined.
It was observed that temperature had a significant influence. Seals staying at the lowest temperature
of 11.9°C and 55% RH displayed the most rapid and the
most intensive crystallisation; after only two months crystals had started to grow on the model
seals. In contrast, those seals stored at the same relative humidity but at 4°C higher had almost no
surface crystalline phase.
Under all tested conditions, seal castings made of 100° and 150°C hot molten mass beeswax
provided a limited surface crystallisation whereas the impregnation with propolis prevented it
completely. Other ways of converting beeswax to a plastic state (kneading, warming under water)
did not have substantially different results from the beeswax heated at lower temperatures.
RESULTS AND DISCUSSION
With the use of GC/MS and DTMS techniques, alkenes with 31, 32, 33 and 35 carbon atoms were
found to be the main (ca. 78.5%) constituents of the crystalline layer occurring on the surface of
beeswax. Their relative amounts were in the following order: C33 > C31 > C35 > C32. Alkenes
with 29, 31, 33 and 35 carbon atoms (maximum at C33) are also originally present in beeswax
itself, but in a substantially lower amount: .5.5%. These beeswax alkenes have mostly a cis-double
bond configuration, so that both hydrocarbon chains connected to atoms of the double bond are on
the same side of the double bond axis. Due to the resemblance of alkenes in crystals and in
beeswax, crystallisation of an unsaturated hydrocarbon fraction of beeswax was suggested as a
phenomenon occurring below the critical temperature, which lies in the temperature range of 12°16°C.
In order to explain the dependence of the crystallisation of beeswax alkenes on temperature,
information about the beeswax structure was collected. The most detailed papers12, 13 point out the
resemblance of beeswax to Fischer-Tropsch waxes, which mostly contain n-alkanes. Identical
difractograms and orthorombic crystals of both waxes are evidence of a similar parallel
arrangement of hydrocarbon chains12. Apart from these crystalline areas, rigid amorphous zones are
present in beeswax. They occur in the surrounding branching of the long chains, in the area of chain
ends due to a wide distribution of chain lengths, and around ester groups, which introduce
disturbances to regular hydrocarbon chains. Mono-esters have been reported to be constituents of
the crystalline phase at room temperature14 and partly of die rigid amorphous phase as found by
Basson and Reynhardt12. The same probably applies to triesters, diesters, hydroxyesters and other
molecules with long hydrocarbon chains and polar groups. The mobile amorphous phase of
beeswax contains the liquid component of the wax12. Although both alkanes and alkenes belong to
beeswax components with the lowest melting points, only alkenes were mentioned as being
possible plasticizers of beeswax15. Plasticizers are reported to be, "non-volatile solvents" of
polymers16,
which suggests the liquid character of alkenes and their presence in the amorphous mobile phase of
beeswax. However, the assumed liquid character of alkenes at room temperature does not
correspond to the melting point of 34°-35°C, which was measured for the alkene fraction after its
isolation using the preparative TLC method17.
A possible explanation was found in a phenomenon observed during a so-called "freeze-drying
process"18. Amorphous systems composed of a plasticizer (most often water) and polymer
molecules are subjected to cooling, which causes water to freeze which, in its solid state, is
removed by sublimation under vacuum. During the cooling stage an interesting effect of water
"supercooling" can be observed. Before freezing water reaches the temperature of -20°C. Based on
the resemblance of both systems (plasticizer and polymer chains), it may be assumed that alkenes
behave comparably. The change of a supercooled liquid of alkenes into the crystalline phase could
be observed during further cooling beeswax from room temperature to temperature lower than
16°C. Interestingly, a very similar temperature difference, i.e. ca. 20°C, between the melting point
and the crystallisation temperature was also observed with the alkenes.
The disappearance of the crystalline layer on the seals was observed after several days of storage at
room temperature. Because of the significant influence of the plasticizer on polymer properties, it
was necessary to find out whether a volatilisation or melting with a subsequent reverse sorption is
taking place after warming the crystalline layer. In the freeze-drying process, a very porous polymer
structure is created enabling a reverse sorption of water or of other plasticizers. A similar reverse
sorption of alkenes into the seal material is assumed, as their volatility is low at room temperature;
Frohlich et al.19 found the vapour pressure of C33H66 to be 2.10 14 kPa. If completely reversible, the
phenomenon of surface crystallisation could be regarded as being not very harmful for the seal.
However, the degree of reversibility is not known and therefore a temperature above 16°C would be
recommended for storing seals to prevent crystal formation.
The porous structure of polymers enabling plasticizer to leach out was also observed in
technological practice16. Surface treatment effecting the less porous character of the polymer was
reported as a possible solution. Dust particles on the seal surface or a propolis impregnation,
similarly, seem to prevent plasticizing alkenes from migrating out of the beeswax seal. However,
the exact mechanism is rather difficult to explain due to the enormous variability of components in
these materials11.
The effect of inorganic pigments inhibiting the surface crystallisation of beeswax was not
investigated in detail. A suggestion was made that pigment particles may work as an interface
between two immiscible phases of alkenes and particu-
larly esters, which are formed under cooling. Adsorption forces between pigment particles and
alkenes may limit the movement of alkenes to the surface.
Limited crystallisation on the surface of seal castings made of 100°C and especially of 150°C hot
molten mass beeswax was observed during our studies. As the effect increased with the
temperature, oxidation or other irreversible reactions were suggested as being the cause of the
degradation of alkenes with a subsequent influence on the degree of surface crystallisation.
The theory of the surface crystallisation suggested for a mixture of stearin and beeswax4 was also
collated with our observations. Changes of crystal structures, caused by the increase in temperature
(polymorphism) were assumed to promote the migration of plasticizers. However, as found by
Basson and Reynhardt12, no change of the orthorombic type of the crystalline structure of pure
beeswax was observed in the temperature range -193°C to 47°C. Moreover, the surface crystallisation of pure beeswax was found to be initiated by a decrease in temperature, in contrast to the
influence of a higher temperature in the hypothesis mentioned above.
Other components of beeswax such as alkanes and esters were also found in small amounts in the
samples. Their occurrence indicates the presence of a small amount of beeswax in crystalline
samples, which most probably originates from beeswax of the seal. A certain amount of beeswax
was possibly scraped off the seal surface together with the crystalline phase, depending on its
character. Samples from seals with well developed crystals (thick crystalline layer) usually contain
only a small amount of other beeswax components and have a corresponding white colour. Less
abundant crystallisation ("blooming") provided yellowish samples with a higher beeswax content.
This is probably because it was difficult to obtain a sample of only the "bloom", without taking
some of the beeswax from the wax of the seal beneath.
CONCLUSIONS
The surface crystallisation of beeswax was studied with respect to historic seals. Alkenes with 31,
32, 33 and 35 carbon atoms were identified in crystalline samples together with other components
of beeswax, e.g., alkanes and monoesters. Alkenes were present in the amount of 42.3-91.1%, and
this variable amount most probably results from the character of the crystalline layer. As the same
alkenes are also present in the beeswax itself, a crystallization of the beeswax fraction of alkenes
was observed on the surface of seals when cooled.
From tests with model seal castings a significant dependence of this phenomenon on the
temperature of the environment was found, with a critical temperature
between 12°-16°C. A moderate crystallisation was observed in the temperature range of 16°-27°C
whereas at 12°C and below an intense and swift crystal formation was observed on the beeswax
surface.
An attempt was made to explain this phenomenon using the information about the structure of
beeswax and comparing beeswax with other systems composed of a polymer and a plasticizer.
Alkenes were suggested to work as plasticizers in the complex beeswax mixture, which are in the
liquid state at room temperature. However, a melting point of 34°-35°C was measured after their
isolation. The difference between the melting and crystallisation temperature was explained by a
supercooled liquid state of alkenes. Under further cooling, a change of this supercooled liquid into a
crystalline solid state takes place. Although this phenomenon is supposed to be reversible to a
certain extent, a temperature of 16°C is advisable as a minimum for storing seals, in order to avoid
large surface crystallisation and to keep the original appearance of beeswax seals.
ANNEXE: ANALYTICAL MATERIAL AND TECHNIQUE
GC measurements
A PU 4600 (Unicam, Great Britain) gas chromatograph with a flame ionisation detector, a split
injector (1/100) and an EC-1 capillary column (Alltech, USA; 0.32 mm i.d., a film thickness of 0.25
μm, a length of 2 m) were used in the measurement. Hydrogen as a carrier gas (lOml/min), air
(16ml/min) and nitrogen as a make-up gas (7ml/min) were employed. The detector and injector
temperatures were set to 350°C and 340°C respectively. The temperature was changed according to
the following program: from 120°C to 340°C at a rate of 10°C/min, 15 min isothermally at 340°C.
Volumes of 0.25-1.0 μl of samples dissolved in chloroform were injected.
GC/MS measurements
GC/MS measurements were performed at the Chemical Institute of the Faculty of Sciences,
Comenius University, Bratislava, Slovakia.
Capillary gas chromatography (Trace GC 2000 Series Thermoquest CE Instruments) with a splitless
injection (after 2min followed by splitting of the flow, 320°C, injection volume of l μl.) onto a 6m
OV-1 fused silica column (0.53 mm i.d., film 0.0002 mm, Ohio Valley Specialty Chemical, USA)
and mass selective detection (Voyager GC/MS Thermoquest Finnigan; ion source temperature of
250 °C, emission current of 30 μA, detector voltage of 250 V, scanning speed of 1.5 Hz and a mass
range of 45-785 Da) was carried out using the following temperature program: injection at 60°C,
15°C/min up to 330°C, 10 min at 330°C. Carrier gas (helium) pressure was adjusted to 20 kPa and
the interface temperature set to 330°C. Samples were dissolved in chloroform. Mass spectra of
peaks were compared with the NIST spectral database.
Direct temperature-resolved mass spectrometry (DTMS) measurements
Analyses were performed in the FOM institute for Atomic and Molecular Physics (Amsterdam, the
Netherlands) on a four sector JEOL SX 102A tandem (B/E-B/E) mass spectrometer (JEOL Ltd.,
Japan). Desorption and pyrolysation of sample on a platinum/rhodium filament (0.5A/min
corresponding to ~20-800°C/2 min) was followed by an ionisation of molecules at 16eV and an acceleration of ions to 8kV. The mass spectrometer was scanned over an m/z range of 20-1000Da
using a cycle time of 0.9 s, with the resolution of the MS system set at 1000. Data acquisition and
processing was carried out using JEOL MSMP9020D data system.
ACKNOWLEDGEMENTS
The authors are grateful to Dr. R. Kubinec (Comenius University, Bratislava, Slovakia) for the
GC/MS measurements and Prof. J. J.Boon and Ing. J. van der Horst (AMOLF, Amsterdam, The
Netherlands) for enabling the DTMS measurements. This work was supported by the Grant Agency
of the Charles University (grant No. 245/1999/B).
SUMMARIES
Surface crystallisation on beeswax seals
Surface crystallisation occurring on seals made of pure beeswax was investigated. The composition
of crystals was determined using gas chromatography (GC), gas chromatography/mass spectrometry (GC/MS) and direct temperature resolved mass spectrometry (DTMS). Alkenes with 31,
32, 33 and 35 carbon atoms and one double bond were found to be the main components. As the
same compounds are also present in beeswax itself, the crystallization of a beeswax fraction of
alkenes was observed. Model seal castings were used for testing different factors, which may
influence crystallisation. A strong dependence of crystallisation on temperature was found and a
hypothesis was proposed explaining these observations.
La cristallisation a la surface des cachets fabriques a base de pure cire d'abeille
Le phenomene de cristallisation se produisant a la surface de cachets fabriques a base de pure cire
d'abeille a fait l'objet d'investigations. La composition des cristaux a ete analysee au moyen de la
chromatographie en phase gazeuse (GC), de la chromatographie gazeuse avec detecteur a
spectrometrie de masse (GC/MS) et de la spectrometrie de masse avec detecteur a ionisation de
flamme (DTMS). Les principaux composants qui ont ete identifies sont des alcenes avec atomes de
carbone 31,32,33 et 35 presentant une double liaison. Etant donne que ces substances sont
egalement presentes dans la cire d'abeille on peut deduire qu'une partie de la cire d'abeille se
cristallise en alcenes. Des experiences ont ete faites avec des moulages de cachets afin de determiner les differents facteurs susceptibles d'influencer la cristallisation. II s'est avere qu'une forte
dependance existait entre la cristallisation et la temperature ambiante. Une hypothese expliquant ce
phenomene a ete proposee.
Die Bildung von Kristallen an der Oberfläche von Siegeln aus Bienenwachs
Die Bildung von Kristallen an der Oberfläche von Siegeln, welche aus reinen Bienenwachs bestehen, wurde durch Gaschromatographie (GC), Gaschromatographie mit Massenspektrometrie
(GC/MS) und temperaturgesteuerter Massenspektrometrie (DTMS) untersucht. Als Hauptkomponenten wurden Alkene mit 31, 32, 33 und 35 Kohlenstoffatomen und einer Doppelbindung
identifiziert. Diese Substanzen sind in Bienenwachs enthalten und kristallisieren aus. Es wurden
Versuche mit Modellsiegeln bei verschiedenem Umgebungsklima durchgeführt, und es zeigte sich
eine sehr starke Abhängigkeit der Kristallbildung von der Temperatur. Es wird eine Hypothese zur
Erklärung dieses Phänomens vorgeschlagen.
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MSc P.Novotná*
Dept. of Analytical Chemistry
Faculty of Sciences,
Charles University,
Hlavova 2030,
128 00 Prague 2
Czech Republic
Tel.+420 2 2195 2300
E-mail: novotna@natur.cuni.cz
Ing. J.Dernovšková
State Central Archives
Milady Horakové 133
160 00 Prague 6
Czech Republic
tel.+420 2 24311509
E-mail: sual@mvcr.cz
* Author to whom correspondence should be addressed