Learn how to construct schematically a stratigraphy


The MiCorr application enables the user to digitally construct stratigraphies that he / she documents either during the visual observation and local probing of artefacts via Bertholon’s method (Bertholon 2000) or the investigation of a sample observed on cross-section.


Visual observation of an artefact under a binocular microscope, (c) Jeanneret.

Fig. 1: Visual observation of an artefact under a binocular microscope, credit Jeanneret.


By observing the artefacts surface under a binocular microscope, the conservation professional tries to understand the stratigraphies of the corrosion forms (Fig. 1).


Schematics of the artefacts cross-sections are drawn to document the strata (Fig. 2). Local probing with a scalpel can also help determine the order of strata and their characteristics (e.g. brittleness, softness).


Schematics of an artefact cross-section and selection of a stratigraphy (red square), (c) Rotzetta.
Fig. 2: Schematics of an artefact cross-section / sample embedded and observed on cross-section and selection of a stratigraphy (red square), credit Rotzetta.


These conceptual models contain information on strata thickness, texture, morphology, composition (if known), and microstructures (for metal and ghost structures). Strata interfaces and markers are also included as they are crucial for identifying the limit of the original surface (Bertholon 2001).


Conservation scientists and / or archaeometallurgists usually have at their disposal cross-sections of samples of corrosion forms. The stratigraphy to represent is deduced directly from the observation of the cross-sections.


It is at this point that the MiCorr application can be used.


Construction of the corrosion strata structure


The user clicks on the Search tool by Stratigraphy Representation as indicated on figure 3.


Screenshot of MiCorr Search tools page.jpg

Fig. 3: Screenshot of MiCorr Search tools page.


A new stratum is added by clicking on “+ Add a stratum” button (Fig. 4). A code with its number is added automatically and highlighted (with the orange rectangular shape on the left of the stratum) to specify the type of stratum: M (Metal), CM (corroded metal), CP (corrosion product), NMM (non metallic material), S (soil), D (deposit), SV (structural voids), etc. The fields of the characteristics (morphology, texture, microstructure, composition, interface) and sub-characteristics of the strata are provided in parallel. They can be filled once a stratum is created or at the end of the construction of the corrosion strata structure (see below). Each characteristic and sub-characteristic is explained by moving the mouse on it.


Screenshot of the Search tool by Stratigraphy representation showing the creation of an “M1” stratum.jpg
Fig. 4: Screenshot of the Search tool by Stratigraphy representation showing the “M1” stratum.


Any new stratum added of the corrosion strata structure is appearing below the previous one (Fig. 5). It is also highlighted with the orange rectangular shape on the left of the stratum. 


Screenshot of the Search tool by Stratigraphy representation showing “M1” and newly added “CP1” strata.jpg

Fig. 5: Screenshot of the Search tool by Stratigraphy representation showing “M1” and “CP1” strata.


Once the corrosion strata structure is completed, the user has to re-locate each stratum versus the other using the arrows included next to each code (Fig. 6). When more than one stratum of a type is considered their number progresses from the exterior to the interior of the stratigraphy.


Screenshot of the Search tool by Stratigraphy representation showing the corrosion strata structure corresponding to the stratigraphy of Fig. 2 cross-section. The thickness field of each stratum has been filled to visualise correctly the structure (ot.jpg

Fig. 6: Screenshot of the Search tool by Stratigraphy representation showing the corrosion strata structure corresponding to the stratigraphy of Fig. 2 cross-section. The thickness field of each stratum has been filled to visualise correctly the structure (otherwise it would be out of the screen).


Building the corrosion form


The next step is to characterize each stratum (Fig. 7). Each field has to be filled to make the comparison with the existing case studies / corrosion models of MiCorr database more efficient. To fill the characteristics the user has to put himself / herself in the position of the observation of the artefact / embedded sample on a cross-section.


Each characteristic / sub-characteristic is explained by moving the mouse on it. If the information under sub-characteristics is not available leave the field blank. Sub-characteristics which are made visible are indicated by an open eye. Those which are not made visible are indicated by a striped eye.


Stratum CM is considered as intermediate between stratum M below and stratum CP above (the ratio M/CP has to be selected from the composition tab). Therefore some characteristics do not need to be filled (texture, interface). New sub-characteristics might be added though (microstructures, additional element(s) in M and CP).

Screenshot of the Search tool by Stratigraphy representation showing the corrosion form corresponding to the stratigraphy of Fig. 2 cross-section once each stratum has been characterized.jpg

Fig. 7: Screenshot of the Search tool by Stratigraphy representation showing the corrosion form corresponding to the stratigraphy of Fig. 2 cross-section once each stratum has been characterized.


Comparing a new corrosion form to an existing corrosion form

The user can question the MiCorr application to find case study(ies) / corrosion models(s) similar to the corrosion form newly built by clicking on the “Find similar” button (Fig. 7). A new window shows up, that gives proposals of stratigraphies from the MiCorr database that are the closest to the stratigraphy just constructed (Fig. 8). The table provided gives for each stratigraphy proposed the score of the matching and additional information on the corresponding artefact.


Screenshot of the list of stratigraphies’ proposals from the MiCorr database that are the closest to the stratigraphy under construction.jpg
Fig. 8: Screenshot of the list of stratigraphies’ proposals from the MiCorr database that are the closest to the stratigraphy under construction.


By clicking on the drawing of stratigraphy and the additional information, the user has access to the characteristics of the stratigraphy and the artefact file of the corresponding artefact.


Saving a corrosion form

The user needs to register to save his / her stratigraphies under his / her profile.


References

- Bertholon, R. 2001. Characterization and location of the original surface of corroded archaeological objects. Surface Engineering, 17 (3): 241-245.

- Bertholon, R. 2000. La limite de la surface d'origine des objets métalliques archéologiques, caractérisation, localisation et approche des mécanismes de conservation. PhD dissertation, University Paris 1 Panthéon-Sorbonne, France. Corrosion doctors: http://www.corrosion-doctors.org/pict-type.htm (accessed 10.19.2015).