Saturday and Sunday, 13 and 14 March, 2010


Unexpectedly the weather cleared in mid-March and ahead of schedule we decided to head to the cemetery with two groups of students on Saturday and Sunday. Using a single camera, battery and light we imaged four stones altogether, two per afternoon. With a group of mostly undergraduate students we managed to capture some great RTIs.

Our first candidate was a heavily weathered stone within the Sir John A. Macdonald enclosure.

We again chose to use the temporary shelter to minimize the sun on the stone. Here are the results:

The results were generally good for the stone of Professor Williamson’s first wife, Margaret Gilchrist,  but the centre of the stone was still very difficult to read, even with specular enhancement. John Granville, the National Historic Sites Program Manager (Eastern Ontario) for Parks Canada, was kind enough to give us a photo of the same stone taken in 1982. The comparison is striking…but more on that in a subsequent post.

We next turned to what we were told is the oldest stone in the cemetery, that of Mary McCrea adjacent to Sydenham Rd. Unlike many of the more expensive monuments in the cemetery, hers was made of local, Kingston limestone that has been very heavily degraded. To the naked eye much of the inscription was unreadable. Here are the results:

Although there was a small shadow at the bottom but the surface normals were still correct on the specular enhancement (image on the right).

The next day, Sunday, we brought our a group of enthusiastic students from the Masters of Art Conservation at Queen’s. We are particularly happy to have their involvement as this sort of documentation work will surely become a standard in their field. We began by imaging a stone that had quite a clear incision, but heavy lichen accumulation. Even with the lichen cleaned off, however, the mostly white granite stone of the marker made it all but impossible to read the text. Here are the results:

Again, shadows marred our final result, but the text was certainly very clear! Our second and final stone for the day was a rather sad case. A marble insert had been placed in sandstone and was buckling due to a century of thermal stress. In fact, the insert was so bowed-out that surface layers of the marble were spalling.

What became immediately clear when we processed the image was that the focus was off during the capture (mea culpa). We can see on the Surface Normal Visualization just what effect this had on the processed results (the planar surface we expect to be blue on a good capture):

We went back to this stone on a subsequent trip to the cemetery (see the next blog entry on 20 March for those results). A lesson was learned! Focus, Focus, Focus.

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Getting Started on the Cataraqui Cemetery Project


It was a sunny, but bitterly cold 6 February 2010 when Alex Gabov, Kate Sullivan and I set out to the Cataraqui Cemetery to make our first RTI captures. We had high hopes for two or three captures, but the -20 C temperatures (-4 Farenheit for our friends south of the border) kept us down to a single sequence: the tombstone of David Kemp. In order to keep down the bright sun we erected a large temporary shelter to block the sun on the stone and we lit a propane heater to keep the living humans warm.

All was going well on the first few images until our flash unit or wireless remote unit (we’ll talk about our equipment on a later post)  began failing. We just couldn’t diagnose the problem…we consulted manuals but the extreme cold meant exposed finger flipping pages were soon numb. Alex and Kate left me and the propane heater in the cemetery while they went back to the studio at Queen’s to figure out the problem. As so often happens, they texted me to assure me that as soon as the re-entered the studio our set-up began working perfectly. The problem: the cold, pure and simple. Our Opus Four-Channel remote was too cold to transmit and Alex was forced to reheat it every five shots in his work van.

So what would have normally taken us only half an hour in normal conditions took us three frigid hours. The results, however, were worth it:

The Normal Visualization feature in the HP PTM viewer disclosed to us an interesting effect we had not fully anticipated. The lichen growing on the stone cause a serious mis-estimation of the surface normals:

This unintended discovery could have real benefits…the surface normal visualization could be used to determine the lichen covering on a stone before and after cleaning by stone conservators.

At the end of the day Alex seemed unaffected by the cold while Kate and I were desperate to return to indoors and process our images.

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IRR RTI using the Osiris


After many months of waiting the new Osiris IRR camera/scanner from Opus Instruments finally arrived. We acquired a few test scans of paintings and test panels around the studio and turned to the long outstanding question of using Reflectance Transformation Imaging in the Infra Red. First a normal RTI using the flash unit in the studio and a digital SLR was obtained.

Default                                                                 Specular Enhancement

Not surprisingly one could study the surface and texture of paint, canvas, craquelure, in-fills and conservation in-painting.

Here is a movie of real time view/manipulation within the RTI/PTM viewer (first half in Default and second under Specular Enhancement)

Next a UV RTI took but an hour – sorry we are having some difficulties with the finished RTI so here is just a still

And finally the IRR RTI which took us a full day. Each scan takes about 15 minutes and thus one must have a ‘stationary’ studio light.

The results were worth the wait.

Default                                                                 Specular Enhancement

See a movie of manipulation within the RTI/PTM viewer (first half in Default and second under Specular Enhancement)

The IR sensor sensitive from 900 to 1700 nm in combination  with the RTI technique is able to compliment VL and UV RTIs and provide us with additional information on under-painting, under-drawing, new and old repairs and their sequence, and some ‘textural’ information not otherwise available. The RTI IRR has a tremendous potential for fine art conservation and historical investigations.

More tests to come…

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