Author Archives: georgebevan

And We’re Back….

After a long hiatus from this blog we’re pleased to return with some reports on new projects. First, we’ll be looking at some of the results from our Coin Identification Workshop this winter in the Department of Classics, as well as some work on watermarks and reverse glass paintings in Art Conservation. The rtiican blog will also be introducing some new collaborators, including Marla Mackinnon, a fourth-year undergraduate at Queen’s who will be working on stereo photogrammetry over the course of the summer.

Stay tuned for more images and text!


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April 10 Workshop: the Final Day.

On our last official day of the workshop we returned to a operating two camera, my D300S and Alex’s new D700.  Among our first goals was to finish imaging the weathered side of a stone that we had failed to adequately image due to a poor light distribution.

Here are the results from the Victor Dupont monument:

The decoration is now clearly visible under specular enhancement and can be compared to the better preserved reliefs on the other side. Note particularly the vegetative relief at the top of the monument.

While Alex was at work on the Dupont stone, I took an experienced team to work on a heavily weathered marble monument on the other side of the stream:

Notice that we are no longer using a laptop with the D300s and are instead relying on an external IR remote to trigger the shutter. Here are the results:

While the surface normals were within bounds on the capture, the veinous character of the marble weathering made reading the inscription difficult under specular enhancement. Considerable post processing will be necessary to reveal all the characters.

Alex’s group then moved out towards Sydenham Rd. where we had early found a small immigrant plot. Hitherto we had only imaged English-language monuments but thought it was important to capture the Asian monuments at the cemetery before the end of the project.

In many cases, these small, inexpensive stones were in the most desperate need of recording. They were insecurely fixed in the ground and their low height meant that they were more subject to damage than the larger, elevated monuments elsewhere. Here are the initial results:

Despite the fact that it was virtually impossible to get a good distribution of light positions due to the fact that the stone was so close to the ground, Alex and his crew did a fantastic job. The normal visualization above shows that apart from a small area on the bottom, the surface normals were perfectly captured. Catrina Caira, a MAC student and among our most dedicated RTI students, was on hand to help us with the Chinese. She determined, with some help from a friend, that the date of death of this individual was 1926.

Here was the next stone in the plot:

In this case the script was virtually invisible to the naked eye. Again, Alex and his team did a great job of capturing the normals despite the physical constraints, as the following visualization shows:

Here Catrina again helped us with a transcription. More on these Chinese stones in the future!

My own final capture was a more traditional Cataraqui stone:

Despite some lichen on the monument the specular enhancement was especially impressive:

Some more post-processing will be necessary for a full transcription, but we were very pleased with the results. Again, the surface normal visualization proved an accurate guide to the location of the lichen growth on the monument:

This stone proved to be lots of fun in post processing.

It was definitely gratifying (and humbling) to see our students picking out names and dates from the RTIs much faster than their teachers. A very promising start to RTI at Queen’s University!


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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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