Silicates present in marls
For dissolving the siliceous part of the marl, the
treatments. These chemical agents do not
attack the carbonated part of the matrix, and
does thus not attack the calcium carbonate of
the eggshells. We have obtained the bests
results by using Potassium Hydroxide (KHO),
which is a great alternative to traditional acid
treatments on this kind of matrix. We can
observe the microstructure of the eggshell with
clarity (Figure 4A), observing even the holes of
the oxygenation channels of the eggshell
(Figure 4C).
Ferric iron in lithified matrices
It is difficult to find a good dissolution agent for
Figure 6: Eggshell treated with Dimetilsulfoxide DMSO at
matrices rich in ferric iron. We have done tests
5% (one week). It is possible to observe the relief and
with both traditional methods and methods of
oxygenation channels (arrows).
other fields of preparation, as archeological
preparation of iron objects. For this reason we
tried Oxalic acid, which is useful to dissolve the
matrix, but also attacks the surface of the
eggshell. The best result was obtained with the
Waller Method (Figure 5A), where we could
observe a good dissolution of the matrix and
little damage on the surface of the eggshell.
The eggshells included in this type of matrix
were the most difficult to clean, due to the
hardness of the sediment. It was necessary to
use an inorganic acid because it is more
reactive. However, this poses a serious risk to
the conservation of the microstructure of the
eggshell. For this reason, we tried to find an
(DMSO; Figure 6). This method al owed us to
clean the surface of the eggshells, without
Figure 7: Eggshell treated with Hydrofluoric acid 5%. The
inducing too much damage.
eggshell relief has been completely lost.
Silicates in lithified matrices
In the last case, due to the composition and
We would like to thank researchers Dr. Bernat
hardness of the matrix, we had to use
Vila and Dr. Albert Garcia (└rea de Mesozoic of
Hydrofluoric acid (HF) 5%, but this did not
the Institut CatalÓ de Paleontologia Miquel
show satisfactory results (see Figure 7),
Crusafont) for the electron microscopy pictures,
because the surface of the eggshell was highly
as well as for their help and support regarding
damaged after this treatment. Further research
several sedimentological aspects of different
is therefore needed for this kind of matrices.
matrices. We also want to thank Judit Marigˇ
Moreover, use of this acid is not recommended
for the English corrections and the reviewers
due to its high risk for the health.
Rui Castanhinha and Femke Holwerda for their
useful corrections.
36 Journal of Paleontological Techniques