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Pritchard Tomb ConservationReport on the Captain Thomas Pritchard Memorial
for the
Old Cemeteries Society of Victoria, British Columbia
By Patricia Leavengood, Art Conservation Services, July 1995 This condition report with recommendations for preservation is based on information obtained during an on-site visit to the Pritchard Memorial May 9, 1995, as well as on written information gathered by Norm Truswell. This information included an analysis of the Pioneer Square sandstone completed by Martin Weaver at the Heritage Canada Foundation laboratory in 1986, excerpts from a geologic survey of Vancouver Island and the Southern Gulf Islands (the likely source of the memorial's sandstone) prepared by the Provincial Government Geology Branch, and a report for the City of Victoria prepared by the Society some years ago regarding the future of the Pioneer Square monuments. The Society also provided elevations of the four sides and top of the monument. Research included telephone conversations with chemists at the laboratories of ProSoCo (manufacturers of stone preservation products), and conservators at the J. Paul Getty Museum and the Los Angeles County Museum of Art. Present Condition of the Memorial
The base of the monument consists of twelve sandstone blocks sited on the rubble and concrete foundation. The blocks support the monument which is constructed in the form of a miniature building.
Surface deterioration of the monument, particularly of areas of the sandstone portions, is extremely severe, disfiguring, and on-going. (Please see attached photographs and drawings) The sandstone deterioration follows a particular pattern which may be crucial in understanding the degradation mechanisms at work on the monument. Most of the losses in the sandstone occur beneath or adjacent to the marble insets and plaques, while the sandstone above the marble, as in the top pediments, the pineapple ornament, and the underside of the central pediment, is in good to excellent condition. The explanation may lie in the deterioration of the marble ( calcium carbonate) into water-soluble calcium sulfate (gypsum) which is washed into the sandstone located directly beneath and adjacent.
Another, although more modest, contributor to the surface deterioration are the lichens and other microbiological growths present. These growths damage the stone mechanically by sending thalli into the pores, breaking down pore walls, and chemically, by secreting acids which break down the mineral structure of the stone. The deterioration of the stone due to other forces, as discussed above, further encourages microbiological growth, and so on in a vicious circle. While there is some surface dirt on the monument, there are no heavy black deposits (the infamous "black crust") often found in urban environments. These crusts are composed primarily of redeposited minerals and salts combined with carbon. Their absence on the monument, and the low incidence of carbon particles in general, indicates that this type of air pollution is rare in Victoria. Recommendations While the removal of the plant materials from around the base of the monument, and the redirection of the lawn sprinklers, is a step in the right direction, the internal causes of deterioration, primarily the deposition and recrystallization of soluble salts, most particularly of sulfates, has not been addressed. Protective Cover It is evident that moisture plays a significant role in the deterioration of the Pritchard monument. The first recommendation, therefore, is to limit water access to the stone. Placing a roof or canopy over the monument will go far to protect it. If the roof extends about a foot beyond the borders of the gravesite, it probably will not need protective sides. (See enclosed sketch) As this will need to be a permanent preservative measure, care should be taken in the design and execution of the protective covering. Further Testing The good news is that sandstone is a material which in many cases is amenable to chemical strengthening and consolidation. The strengthening is accomplished by the use of silicic ethyl esters. The consolidant is applied in an extremely low-viscosity liquid form, which penetrates deeply into the stone structure. A catalyst causes the liquid to gel and then solidify into silicon dioxide (a glass -like material) within the stone. This new mineral structure consolidates the damaged stone. This material has been used in Europe since the 1960's, and much has been learned during the past three decades about the factors which lead to success or failure of this consolidation system. A U.S. company, ProSoCo, has recently purchased the formulas and technology from the German manufacturer, Wacker-Chemie, and now produces silicic ethyl ester formulations in the U.S. Because of the multiple factors which affect the performance of the sandstone consolidant, including the composition of the stone, the presence of salts, the condition of the surface and interior, and the environmental conditions of the affected stone, ProSoCo requires analysis and testing of the stone before a positive recommendation can be made to. use the consolidant. (There have been cases where using the consolidant without pre-testing, where conditions were not appropriate for its use, has led to severe stone damage). The tests that were performed by Martin Weaver are of some help in this regard, because they characterize the stone fairly well. His analysis is, however, qualitative rather than quantitative (i.e. sulfates are present—but we do not know in what concentration and distribution) and ProSoCo requires quantitative analysis. In addition, a water absorbency test is required, which indicates how the consolidant should be applied in order to gain maximum penetration. Samples for these tests will seem shockingly large at first. ProSoCo requires at least two core samples, and more if possible, which are 1.5 inches in diameter and 4-6 inches long. It should be noted, however, that the tests are non-destructive for the most part, only a few millimeters are removed, and the remainder of the cores are returned for reinsertion in the monument. The cost for the basic analysis is $1500. The information gained from the analysis is crucial in determining not only whether or not the consolidant can be successfully used, but also the correct method of application, whether the stone should be cleaned before or after consolidation, how the marble insets and plaques should be treated, and which of the formulations is the most appropriate. In addition, the chemists at the ProSoCo laboratory provide help in designing a treatment plan and support during the application process and subsequent curing period. (Please see enclosed information on "Conservare" stone strengthener). I have carefully considered the possibility of having another lab, such as the Canadian Conservation Institute, perform quantitative analytic tests on the stone which could then be forwarded on to the ProSoCo lab, in order to save money and to have a second opinion. In the end, however, ProSoCo will still have to perform absorbency tests in order to determine the application method, so I doubt if much money would ultimately be saved. I would suggest, however, that an independent chemist, either at CCI, or one I frequently consult at the Los Angeles County Museum, be hired to review the analysis and recommendations of the ProSoCo lab once these are completed. I have sent the ProSoCo lab a spalled sample of the Pritchard monument sandstone, as well as photographs, and have been assured that this type of sandstone can be successfully consolidated. The next step in the process would be to take core samples from representative areas of the monument and forward them on to the ProSoCo lab for analysis. Treatment The treatment of the Pritchard Memorial must be approached holistically rather than piecemeal. Eliminating water from the structure by means of a protective canopy and deflection of the lawn sprinklers will do much to arrest the on-going deterioration processes which are triggered by moisture. This will not, however, prevent further erosion of the friable surfaces from wind and handling by people. This crumbling away of the monument can only be addressed by consolidation, and the consolidation must be of the entire monument. It is likely that the marble sections of the monument will be treated differently than the sandstone in terms of coatings or consolidants, depending on test results. In addition, the exposed iron pins should be sealed and the missing marble corners infilled with an appropriate fill material to further isolate the iron from moisture sources. The cleaning of the stone and removal of microbiologic growths will most likely follow, rather than precede consolidation, due to the extremely friable nature of the stone. A water repellent will most likely be applied to the sandstone after consolidation and cleaning. The final stage of treatment would be cosmetic, that is the patching, filling, or re-creation of lost areas. The degree of aesthetic restoration of the monument may be determined at a later time and as the budget allows once the monument itself is stabilized and the stone is strong enough to allow for mold-taking, should that degree of restoration be desired. Treatment Priorities Immediate:
Mid-term:
Long-term: 5 Aesthetic re-integration by patching, filling, or restoration of missing parts |
The Captain Thomas Pritchard Memorial monument was designed by Victoria architect Thomas Trounce and erected in 1872. It is composed of a local sandstone, probably quarried from Thetis Island, with marble insets and plaques. Originally the monument was surrounded by a low wrought iron fence, which has subsequently disappeared. The monument is in the high Victorian style, in the form of a four-sided square structure with pillar/pilasters, pediments, and carved lintels, surmounted by a pineapple ornament.
Structurally the monument is sited on a bed of rubble and concrete which begins about one inch below grade to a depth of 15 inches, where it then extends out from the monument about 12" on all sides. This foundation is stable and the monument is completely plumb.
Four corner pillars are infilled with large white marble insets, surmounted by a lintel, pediment and smaller pedimented cube. This smaller cube is probably formed from a solid piece of sandstone, and has one white marble plaque affixed to each face. The pediment surrounds a quarter gable roof surmounted by a sandstone pineapple ornament. The sandstone corner pillars have been set with vertical bedding planes, and consequently are much deteriorated. The marble insets on the lower section of the monument are held in place with iron cramp irons. These have rusted and expanded, breaking the marble in the upper corners of each of the four insets. The upper marble plaques show rust-colored staining but no visible iron attachments, and structurally they appear to be stable.
The interior construction of the lower part of the monument is unknown, while it is probable that the upper portions consist of solid sandstone blocks to which the pediments, ornaments, and marble plaques have been affixed. Tapping the lower portion of the monument produces a hollow sound. However, it is possible that a rubble or brick interior support structure exists, which is or has separated from the outer monument walls. In order to learn more about the interior of this part of the monument some probes should be made at the join of the sandstone and marble inset. This can be done with a long thin metal probe, and should be attempted on all sides of the monument. This might involve some drilling or mortar removal at the join line of the two stones.
As the stone dries, the newly deposited sulfate crystallizes within the pores of the sandstone, breaking apart the matrix of the stone. The deterioration of the marble into calcium sulfate is attributable to air pollution and is a phenomenon observed all over the developed world. In this instance not only do we see surface erosion and loss on the marble surfaces, but we see that the lost material, in the form of soluble salts, is contributing to the deterioration of the sandstone into which it has migrated.
Another source of soluble salts could be from a degraded gypsum plaster coating which apparently at one time was applied to the lintel and base directly above and below the marble insets, possibly as an attempt to halt the deterioration in these areas. There are only remnants of the plaster yet remaining, but perhaps old photographs will give information about the extent of the plaster work and the period of application. Migration of calcium sulfate from the plaster directly into the stone and then subsequent recrystallization would explain the particularly heavy losses in these areas.
Other degradation mechanisms are certainly at work as well. For many years there was plant material around the base of the monument. If this plant material was fertilized, soluble nitrates would be wicked into the stone from the surrounding soil, recrystallizing within the stone as in the case of the soluble sulfates described above. In addition, the watering of the plants and of the cemetery lawn by sprinklers which were not directed away from the monument no doubt contributed to the dissolution and recrystallization of soluble salts in the structure. The wetting and drying cycles, and the prolonged saturation of the base of the monument due to watering and adjacent plants, accelerates normal mineral dissolution and redistribution within the sandstone, causing further damage to the pore structure of the stone.
As mentioned above, the construction of the monument utilizing sandstone laid with vertical bedding planes, as in the corner pillars, is contributing to the monument deterioration. The vertical planes allow for easy and rapid penetration of water deep into the stone structure, where mineral dissolution occurs. As the water evaporates from deep within the stone, it brings to the surface solubilized minerals which are redeposited at or just below the surface. These minerals build up to form a surface layer with different chemical and mechanical properties than the surface immediately below. Often this surface layer is harder than the interior of the stone, and has more densely packed minerals, such as iron oxides, which have been redeposited there. Eventually this surface layer spalls off, revealing the weakened stone interior which is easily eroded by rain and wind. This type of erosion is in evidence all over the base of the monument. A further consequence of moisture trapped within the stone is that during freeze-thaw cycles water will crystallize into ice, breaking apart the pore structure just as soluble salts do.