Val et al., 2014: CHEMICAL PREPARATION OF DINOSAUR EGGSHELLS
citrate,
sodium
bicarbonate
and
sodium
However, due to the hardness of these
dithionite. This method does not use acids, and
matrices, we had to test EDTA at 5% with
therefore, dissolution of the calcium carbonate
sodium hydroxide at 4% (see Figure 5C), in
of the eggshell is avoided. Dithionite reduces
order to dissolve them (Fernández et al.,
ferric iron to ferrous iron, which is soluble;
2005). Sodium hexametaphosphate (NaPO3)6,
citrate sequesters ferrous iron; and bicarbonate
when used in combination with the Waller
buffers the pH to maintain the solution neutral.
Method, had to be diluted at 15% (see Figure
Additional treatments for dissolving concretions
5D), in order to make the products more
of iron oxides, and tested herein include Oxalic
reactive. Table 3 shows the concentrations and
acid (H
2C2O4) and ethylenediaminetetraacetic
results for each treatment.
acid (EDTA; see Figure 5B; Mourey, 1987).
Table 3: mixtures for carbonate in hard matrices with ferric iron.
CHEMICAL AGENT
%
OBSERVATIONS
Waller Method:
Optimal cleaning (Figure 5A)
Sodium citrate 71 gr.
-----
Sodium bicarbonate 8.5 gr. Sodium dithionite
20 gr.
Ethylenediaminetetraacetic acid (EDTA)
C
10H16N2O8
5%
Not effective cleaning (Figure
5B).
Ethylenediaminetetraacetic acid (EDTA)
C
10H16N2O8
5%
Surface
slightly
eroded
Sodium hydroxide
NaOH
4%
(Figure 5C).
Sodium hexametaphospate
(NaPO
3)6
15%
(Figure 5D).
Waller Method
----
Oxalic acid
H
2C2O4
10%
Surface slightly eroded
Table 4: organosulfurs.
CHEMICAL AGENT
%
OBSERVATIONS
Dimetilsulfoxide DMSO
CH
3SOCH3
5%
effective cleaning (allows to do an
study of the surface) (Figure 6)
Table 5: agents for hard silicate matrices.
CHEMICAL AGENT
%
OBSERVATIONS
Hydrofluoric acid
(HF)
5%
Surface highly damaged (Figure 7)
Organosulfur:
for
Oncolitelimestones
DISCUSSION AND CONCLUSIONS
(dissolving very hard matrices)
Oncolitelimestone matrix is highly carbonated
Carbonated matrices in sandstones
and its dissolution is very difficult without using
strong acids. In this case we have used a
For this kind of matrix, the best option for its
chemical agent not used in any previous
dissolution with acids proved to be the
analysis.
It
is
an
organic
solvent
treatment with Oxalic acid (H
2C2O4; Figure 3C).
(Dimetilsulfoxide (DMSO):
CH3SOCH3) that has
This kind of chemical agent is a good
been used for the dissolution of very
alternative to the traditional organic acids used
compacted and lithified matrices (Triplehorn,
for dissolving carbonated compounds, like
2002; Triplehorn et al., 2002). Its disadvantage
acetic and formic. The effect of Acetic acid
is that it can take weeks to break up the
(CH
3-COOH (C2H4O2)) is stronger and more
matrix. However, it was the only treatment that
harmful compared to oxalic acid (Figure 3C).
worked well with this type of matrix (Figure 6).
However, oxalic acid is difficult to neutralize
Table 4 shows the concentration for obtaining
completely, and thus remains somewhat
the best result with this treatment
harmful on the surface of the eggshell (Figure
3C). The worst result was obtained with HCl
Agents for hard silicate matrices
(Figure 3B). On the other hand, the use of
It is known that hydrofluoric acid (HF) is a good
Sodium hexametaphosphate (NaPO
3)6 with a
silicate solvent. However, it did not provide
pH value of six has proved to be a good
very good results during our essays. Table 5
cleaning method. It is better than Oxalic acid,
shows the concentration and the result with
because less damage is induced to the surface
this treatment.
(Figure 3D).
35
Journal of Paleontological Techniques