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ATR-FTIR analysis.

The spectrum for a known genuine patina sample is clearly a crystallised precipitate of carbonate: most probably aragonite or calcite. These CaCO3 minerals, which are amorphous CaCO3 exhibit only very slightly different IR absorptions, hence calcite serves as a straight-forward reference.

IR spectroscopy is a powerful tool when it comes to the analysis of chemical bonds. The incident light excites molecular vibrations and we observe a signal attenuation in the region that is characteristic for a certain molecular motion (stretching, deformation or sometimes also torsions). The absorptions in the spectra show mainly stretching motions that are due to the CO3 part of the CaCO3 molecule. However, comparing the authentic patina sample with the fake samples and the calcite reference, it is noticeable that the region around 1000 cm-1 exhibits a very clear signal in both the confirmed fake patina spectrum as well as in the spectrum of the kotyle 'patina'. Equally, a feeble band near 800 cm-1 is observed which  is missing in the genuine sample and in the calcite reference.

Let us compare the fake with the calcite and quartz spectra.

It is very noticeable, that the kotyle shows a peak that has the same characteristics as the main peak in the quartz spectrum - it is due to asymmetric stretching motions in the quartz structure. Equally, the aforementioned absorption near 800 cm-1 can clearly be attributed to symmetric Si-O-Si motions.

Here the spectra are overlaid one upon the other.

Clearly, the calcite and the quartz references indicate that the patina of the fake kotyle consists of carbonate minerals as well as of finely powered quartz sand. Of course, other Si containing substances could be present. IR spectroscopy is not particularly strong in ruling out similar compounds consisting of the same chemical bonds. For an accurate determination of the crystal structure, powder X-ray diffraction techniques are well established.

Finally, there is one absorption left to discuss that is of great importance: the three small bands just below 3000 cm-1: These are vibrations due to stretching motions of organic compounds and thus most probably originate from the glue that was used to apply the fake patina. In the first spectrum of the kotyle, you will also see these bands: they are very weak but they are definitely present.

So we come back to the piece we started with.

Similar test results would without doubt be found with this piece too.

But there is more to tell.

This is an extremely important book - buy a copy!

In  the book you wil find ...... the very same piece!

More an more appearing  on eBay.

Here is another from the same workshop and by the same hand.

More types.

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