Tuesday 28th June 2011; Theory into Practice & Visit to Basilica di Sant'Andrea della Valle

Week 11 of 12 
Module 6: Synthesis


Gionata Rizzi joined us for the last time this morning to discuss putting 'Theory into Practice'. He then presented us with a case study of the archeological site of Jerash in Jordan and we separated into groups to discuss how we would approach a particular part of the site.

This afternoon we had our final site visit which was to the Basilica di Sant'Andrea della Valle to listen to a presentation from the site architect and the conservator, and then to view the result of the cleaning work carried out on the facade.

 The Basilica di Sant'Andrea della Valle.

Looking upwards at the facade of the Basilica di Sant'Andrea della Valle.

Monday 27th June 2011; Presentation of Cimitero Project Work

Week 12 of 12 
Module 6: Synthesis / Cimitero (Non-Catholic Cemetery) Project


This morning we gathered at the Non-Catholic Cemetery to present the work that we have carried out over the past week on six of the tombs to our course colleagues, Non-Catholic Cemetery staff and associates, Getty Conservation Institute staff and ICCROM staff. The additional people present were Amanda Thursfield (Cemetery Director), Nicholas Stanley-Price (Non-Catholic Cemetery), Rita Galluccio (Cemetery Conservator), Jeanne Marie Teutonico (Associate Director, GCI), Susan MacDonald (Head of Field Projects, GCI), Kecia Fong (Project Specialist, Education, GCI), Simon Warrack (ICCROM stone consultant and Stone Course Coordinator), Cristina Cabello-Briones (Stone Course Assistant), Estefania Lopez Gutierrez (ICCROM intern) and Gionata Rizzi (architect and Stone Course lecturer).


'Before treatment' photos of the tombs can be seen on 'Monday 23rd May 2011; Microbiological Deterioration'. Below are photographs showing the tombs as they appear now. Most of the tombs still require a small amount of work which will be completed over the next month or so. I will later add some details about the types of conservation interventions we employed, they included applying biocides, poulticing of various types and consolidation.

The Russian Tomb.

Tomb for Violet May Court.

Tomb for Osgood Field and Katharine Roxana Parker.

Tomb for Florence Baldwin (1918).

Tomb for Belinda Lee.

Tomb for Herman Wichmann.

Monday 20th June 2011 - Friday 24th June 2011; Cimitero Project Week

Week 11 of 12 
Module 6: Synthesis / Cimitero (Non-Catholic Cemetery) Project


This week we have the opportunity to put the theory that we have learnt over the duration of this course into practice. We will be implementing the conservation plans that we have devised for our assigned tombs at the Non-Catholic Cemetery (see various posts including 'Monday 23rd May 2011; Microbiological Deterioration' with photographs of all of the tombs being studied) along with the ICCROM, GCI and Non-Catholic Cemetery staff.

Friday 17th June 2011; Vegetation Control & Biology Laboratory Session

Week 10 of 12 
Module 5: Conservation Interventions and Treatments; Criteria for Selection and Implementation


Today we were rejoined by Giulia Caneva (see Friday 20th May 2011; Biodeterioration) who gave us a lecture on 'Vegetation Control'. Following this we had a laboratory session with Giulia and Ornella Salvadori looking at the samples of biological material that we had removed from the tombs that we're conserving in the Non-Catholic Cemetery and other samples of biology to aid our understanding and identification skills. More details to follow...

Image of moss identified on the tomb of Florence Baldwin, which Anita (Australian participant) and I are conserving, through the lens of the stereomicroscope. Image c.10mm wide.

Thursday 16th June 2011; Diagnosis & Treatment of Granite and Bioremediation

Week 10 of 12 
Module 5: Conservation Interventions and Treatments; Criteria for Selection and Implementation

This morning Jose Delgado Rodrigues, Geologist and Conservation Scientist at Laboratorio Nacional de Engenharia Civil, spoke to us on his specialist subject; granite. Granite is a holocrystalline material (entirely formed from crystalline minerals) and when formed is virtually non-porous. Its formation occurs deep within the earth at high temperature and under pressure. The processes by which the granite reaches the Earth's surface result in the alteration of some minerals, weathering and creation of a certain level of porosity due to the contraction or movement of crystals as they form. For this reason the majority of granite that is quarried and has been used in construction is already in a state of decay that has occurred over a geological timescale before being exposed in its use as masonry. The granite that is present in Scotland is one of the exceptions to this rule because the glaciation that occurred during the Ice Ages removed the upper surfaces of the granite outcrops exposing 'fresh' granite. For this reason, the types and issues of deterioration of granites that we face in Scotland are much less serious than are faced in countries where the stone was quarried in an already highly altered state.

Although it is generally unknown, granites do have a porosity, although this comes in the form of fissures and micro-fractures rather than rounded spaces connected by thin necks. The spaces are created by various processes including the different characteristics of the quartz and feldspar crystals which have different modes of elasticity and strength. The fractures are generally very well connected resulting in the granite having a notable permeability. More details to follow...

This afternoon we were rejoined by Ornella Salvadori (see Monday 23rd May 2011; Microbiological Deterioration) who spoke to us on the subjects 'Control & Prevention of Biological Growth', 'Methods of Evaluating Biocides' and 'Bioremediation'. Ornella has recommended us the book; Charola, McNamara & Koestler, 2011. 'Biocolonization of Stone: Control and Preventative Methods' (free PDF download available by clicking here). Lecture details to follow...

Wednesday 15th June 2011; Desalination, Underwater Conservation & Community Engagement

Week 10 of 12 
Module 5: Conservation Interventions and Treatments; Criteria for Selection and Implementation

We continued on from yesterday (see Tuesday 14th June 2011; Desalination) on the topic of desalination today, with a lecture and then a follow-up session in the ICCROM laboratory with Veronique Verges-Belmin. We were shown how Mercury Intrusion Porosimetry can be used for identifying pore sizes in poultices although it cannot measure pore sizes over 200μm, or those that are significantly small. Tests on some poultices were carried out in a study (reference can be located if requested) that showed how vastly different the pore sizes in different poultice compositions can be and therefore the potential options for desalination of stones with particular porosities. The pore size range was from fume silica with pores 0.005-0.05μm in size to pores c.180μm in size in a 0.5-1mm sand.

We discussed the difference in water content possible in different types of poultice and looked at a graph that identified how there is generally an optimum water content in different poultice compositions. Once you cross the optimum water content you soon find that you have an unusable slurry and adhesion to your substrate is no longer possible. The water content in a poultice can also affect the level of shrinkage that occurs upon drying which is important because this is related to adhesion. If a poultice partially detaches from the stone substrate then the danger is that water migrating back towards the surface will deposit as efflorescence and subfluorescence within the stone rather than within the poultice. Although it may seem logical to have a very wet poultice, or to pre-wet your stone prior to poulticing, the danger is that you will drive the salts deeper into the stone and then will not be able to remove them with your poultice. A poultice that works by advection will really only remove the salts from the outer 20-40mm of the stone and will never result in a complete extraction of salt from the stone substrate.

We revisited our poultice samples made up yesterday in the second half of this morning, and the findings that came from the tests concurred with the theories we were taught yesterday and this morning. These include that thinner poultices result in lower levels of shrinkage, that increasing the sand content in a poultice results in a lower amount of shrinkage (same mechanism as in a mortar) and that the cellulose poultice with the longer fibres resulted in a lower level of shrinkage than the one with short fibres. Many new poultice materials are coming onto the market and each needs to be carefully assessed before it's applied for its suitability for a substrate and to identify if it may already contain salts- clearly not a desirable quality for this purpose!

The poultice samples that Rutger (Dutch participant) and I made using two types of cellulose poultices on sandstone, brick and volcanic tuff.







This afternoon we were joined by Barbara Davidde, Director of the Underwater Archaeology Operations Unit at the Instituto Superiore per la Conservazione ed il Restauro. The underwater archaeology unit was set up in 1997 and is an office of the Italian Ministry of Culture. Although historically it was common to remove archaeological finds from underwater, the current aim is always to preserve them in situ wherever possible. Lime mortars with a hydraulic set (either naturally or those which have a pozzolanic content) can be applied underwater directly onto the stonework, although different application techniques are required. The biggest problem that underwater stone objects or structures face is biological colonisation, although there are also human issues such as boat anchors damaging sites and unmonitored underwater tourists. These objects do not however, have issues with water or salts because these stay in a constant state- the salts are always in solution. Biological growth needs to be removed mechanically underwater as a biocide could not be constrained to a specific object. It is possible to protect certain stone objects from deterioration in similar ways to those above water level such as covering mosaics that have been conserved with geotextile sheeting. Despite the aim to keep as many objects in situ underwater as possible, it is common for limestone or marble sculptures to be removed because they are much more prone to serious macro-biological attack by organisms that bore into their surfaces.

Simon Warrack, ICCROM Stone Conservation Course Coordinator, gave us the last lecture of the day on 'Ta Reach- Sculpture Repair'. Simon talked us through the long and interesting history of Cambodia and the use of the Angkor Wat temple since its initial construction in the 12th Century. It was constructed as a Hindu temple but through the centuries fluctuated between use as a Hindu and as a Buddhist temple depending on the rule of the country. The change from Buddhist to Hindu use in the period 1243-1295 saw the destruction of all Buddhist symbols present at that time, or their adaptation to Hindu symbols. When the French arrived in 1860 the temple was Buddhist, but due to the conservation principles followed at the time, the hundreds (or possibly thousands) of Buddha sculptures or religious donations or offerings were removed from the temple to return it as closely as possible to its original Hindu structure. No thought seems to have been given to the thousands of Buddhists who used this temple for worship at that time.

The focus of Simon's lecture was on a single statue which many believed to be the Hindu god Vishnu (probably why it was never removed at the end of the 19th Century), but it is now generally accepted that it is a manifestation of a Buddha. This sculpture is a very important symbol for the Buddhists who visit Angkor Wat for worship. In the 20th Century the sculpture was restored and new cement arms and head were added where they had been missing. Simon was involved in the conservation of this sculpture and due to the 'living' nature of this piece of cultural heritage, community consultation was seen to be an essential part of this project. Through community consultation it was agreed that it was essential for the sculpture to retain its full set of arms and head, but that new arms were to be carved from stone and following three years of research and discussion the head was located, which had previously been removed, and it was returned to site and put in place. This is a very simplified version of the story Simon told and it was a really nice case study of the need for us to recognise 'living' heritage. It was an example of a project where it was necessary to bend some of the rules laid out in the various conservation charters (the 'restoration' of missing parts) and to appreciate the current use of the site as one of its most significant values. Simon made a video about this project that includes all of the details that I have missed out (and may correct any details that I have confused), which can be seen on youtube.com by following these links; part 1, part 2, part 3, part 4.

Tuesday 14th June 2011; Desalination

Week 10 of 12 
Module 5: Conservation Interventions and Treatments; Criteria for Selection and Implementation

Today Veronique Verges-Belmin, head of the stone department at the Laboratoire de Recherche des Monuments Historiques (one of the three state laboratories of the French Ministry of Culture), joined us to speak on the subject of desalination. Veronique started the class with two simple demonstrations to illustrate the two different ways that salt can be removed from a stone; advection and diffusion. Advection is a process whereby water is sucked from a medium by a second material with smaller capillaries. This was demonstrated by sucking up water into a small glass capillary tube and then placing a smaller tube into the end containing water- the water was immediately sucked into the smaller tube. We then did the reverse of sucking water into the smaller capillary tube and placing this at the end of the larger capillary tube- no water movement occurred. The point of the demonstration was to say that when you use an advective desalination process (e.g. poulticing), the poultice material must have smaller pores than the substrate. Diffusion is a process whereby ions move from a more concentrated solution towards a less concentrated solution; this was demonstrated by dropping a small amount of ink into a glass of water and watching the ink slowly disperse through the water and sink. An example of a diffusion desalination process is using a water bath where the higher concentrations of soluble salt move out of the stone towards the areas of lower concentrations.

The examples given above of poulticing and water baths are the two most common forms of desalination carried out but many other methods exist and are used either as stand-alone techniques or in combination with other techniques. Some of the other techniques highlighted were;
*Removal under a vacuum; water is sucked through your object by a vacuum and transporting soluble salts with it.
*Water pressure; water is pushed from one side of an object through to the other side transporting soluble salts with it.
*Dry removal; salt efflorescence is brushed from the surface of a stone.

Alison Heritage also rejoined us this morning (see Thursday 19th May 2011; Salts for details on previous lectures) to discuss the complications and risks of poultice salt extraction. Two of the issues we discussed were the potential for a poultice to leave a residue on the surface of the stone and the potential alteration of the salts that are present in the stone due to selective extraction. The poultice that provides the greatest adhesion will not always be the most appropriate poultice for a job because, especially in the case of kaolin-based poultices, there is often a problem with residues being left on a stone's surface. Cellulose poultices are generally considered to be possible to remove easily from most stones, however their capillary size may be too large for many stone substrates. The concept of selective extraction of salts is an interesting one. You will naturally remove the more highly soluble salts first, or more efficiently during a poulticing procedure and therefore you have the potential to alter the salts remaining in the stone into a more dangerous state. Alison's aim was not to put us off poulticing, but to make us aware of the issues involved, concluding that we should should not be put off poulticing, but that we should always use pre- and post-treatment assessments to inform our decisions on whether we should repeat, adapt or abandon poulticing on a case-by-case basis.

Veronique then spoke to us about the 'Influence of Components on Poultice Characteristics'. Details to follow...

This afternoon we had a practical lab session in groups of two trialling different types of poultices and different methods of application with a variety of other variables. We will be revisiting these tests in the lab session tomorrow morning to see and discuss the results of the tests.

Preparing our consolidation samples on sandstone, brick and volcanic tuff.

Monday 13th June 2011; Rock Art Conservation & Cimitero Biocide Treatments

Week 10 of 12 
Module 5: Conservation Interventions and Treatments; Criteria for Selection and Implementation


Andrew Thorn, a conservator from Australia, came to talk to us today on his specialism; rock art. One of the main focuses of these lectures was the philosophy and human understanding related to this type of conservation. Andrew's experience of this work includes a large number of cases where the rock art still belongs to a group of people or community; generally an indigenous population. This introduces many more considerations than simply rock art as a piece of a heritage long-gone and the significance of the work or surrounding environment must be treated in a very different way. Andrew believes that a strong and trusting relationship between himself and the custodian(s) of the art are necessary, along with a respect for the related culture and community, although he believes it to be necessary to take a 'professional disinterest' in the significance of the art. That is not to say that he is not interested in its origins or meanings, but that they are not required for him to do his job and in many cases they are either secret or private symbols, meanings or stories. If the information is available for him he will find this out in time, but not by asking.

This topic led to a discussion about how the interaction of a community group with an object can vastly affect the approach taken. Andrew showed us an example where a termite nest had grown rapidly and concealed an area of rock art and with the agreement of the community this was carefully removed by a conservation procedure and the art work revealed. Simon Warrack at this point gave an example where a 4m high turmite nest has grown in Angkor Wat (see Friday 10th June 2011; Water repellants, Consolidants & Conservation of Paint on Stone) but which has not been removed because it has taken on a level of significance. The nest is believed by many to have grown into the form of a Buddha and is now considered to be a sacred monument and in addition, because the site has a history of Buddhism, the turmites cannot be killed. An interesting point in relation to 'living' pieces of rock art is that the markings may not be the thing which has the most significance to the custodian(s) or community; it is often the rock itself which bears the meaning and therefore conservation interventions need to be considerate of this point. A consolidation treatment may save the superficial markings but they may be considered to damage the significance of the site.

Rock art tends to fall into two categories; 1. engravings into the rock surface (hammering often used) and 2. paintings or markings applied using a different material onto natural rock surfaces. Andrew argued that the significance of a site tends not just to be in the image alone, but that the whole context of the site and its surrounding area need to be considered. Salt damage is an even more complex problem in the case of rock art than it is in buildings, because you do not have the same options of desalination or damp proof courses. If you do try to remove a salt via a poultice you face an additional danger that more salts will be transported into this area by osmosis which may enhance the previous damage.

This afternoon we visited the tombs that we're working on in the Non-Catholic Cemetery to make decisions on (and in some cases apply) biocide treatments. Anita and I assessed the tomb of Florence Baldwin that we're working on and following a debate and discussion with others took the decision not to apply a treatment. This decision was based on the fact that we could not observe any damage related to the presence of biological growth and we do not believe that the biology present detracts from the appearance of the tomb. We still have to decide if we will remove some or all of the lichens mechanically at a later stage based on damage risk and aesthetics.

Several of the various forms of biological growth present on the tomb of Florence Baldwin can be seen in this image including the darkened upper surface, yellow lichen growth on upper surface and white lichen growth on the side of the tomb.

Friday 10th June 2011; Water Repellants, Consolidants & Conservation of Paint on Stone

Week 9 of 12 
Module 5: Conservation Interventions and Treatments; Criteria for Selection and Implementation


We had our first official lecture from Simon Warrack the Stone Conservation course co-ordinator this morning discussing his experience of 'Working with 'Reversibility'- Case Study at Angkor Wat'. A huge conservation project has been underway at Angkor Wat, Cambodia, since (I believe) the turn of this century. There were about four zones, which Simon highlighted, that were considered to be in the worst state of deterioration at the start of this project, each for different reasons; water ingress, collapse and previous conservators! Simon was keen to say that many of the previous conservation 'mistakes' were simply due to the accepted conservation practice at that time, which were then considered correct. It is only since then that we have been discovering the negative aspects of many of these treatments. The main point of the presentation was the discussion about 'reversibility'. Simon showed us how a resin coating had been applied inside a temple on some very fine carved work all around the walls, which would have been justified at the time due to its ability to be reversed, i.e. if you put the resin in a solvent it can be dissolved and therefore in theory it can be removed from the stone. In practice, however, the resin caused a great deal of damage due to its impermeable nature and was causing a large amount of damage to the stone behind and serious losses in detail to the surface. Following many trials they did identify a method for removing much of the resin, but considerable loss of the stone's surface had occurred and consolidation was required. The removal, I understand, took 4 years and when you consider it probably took just a few days to apply does this really make the concept of reversibility desirable?

We received additional lectures from George Wheeler and Gottfried Hauff on 'Water Repellants', 'Evaluating the Performance of Consolidants' and on the 'Conservation of Paint on Stone'.

Details to follow...

Thursday 9th June 2011; Consolidants- Lab Tests, Evaluating Performance & Durability

Week 9 of 12 
Module 5: Conservation Interventions and Treatments; Criteria for Selection and Implementation


This morning we had a lab session with Gottfried Hauff, a professor and head of the Stone Conservation Course at the Department of Restoration, University of Applied Sciences Potsdam, investigating the effect of porosity on the use of consolidants. We carried out tests on different types of stone using Karsten tubes (Rilem tubes) and identified the wide variations in capillarity between different types of stone and between three stones of the same group (i.e. three sandstones). Gottfried highlighted the importance of always recording the size of the tube opening that you are using because you will get quite different results with a 2cm opening and with a 4cm opening. If you want your work to be repeatable or to be used by others in future for comparisons it is essential to record this information. There are also likely to be slight deviations in the opening size where the putty used for fixing the tube blocks part of the opening; a clever suggestion for accurately recording this size is by taking an imprint of the putty with an ink pad following the test and printing it beside your results from which the opening area can be calculated. Ideally you would always use the tube with the largest opening because it is supposed to be more accurate, but this is not always possible on curved surfaces. As with other test methods you need to be careful which area you select for carrying out the test because the putty tends to leave a slight mark on the stone due to its oil content.

The Karsten tube (Rilem tube) test for capillarity on a cube of sandstone.











We also discussed another technique for identifying the capillarity of a stone, which is a simple 'drop test' where a drop of water is put onto the surface of a stone and the time it takes (in seconds) for this to be absorbed is recorded. This test is good in that it allows you to identify how much the capillarity varies across the face of a stone. This test is most useful as a comparative test rather than as strict quantitative data. To increase the accuracy it is possible to use a 'norm pipette', which produces water droplets of fixed sizes- this is a simple but very effective piece of equipment I'd like to get for my work at the Scottish Lime Centre Trust.

The 'norm pipette'.









The second test we carried out was to trial several different alkoxysilane consolidants on cubes of a single type of sandstone. The cubes of stone were placed into small pools of each consolidant and the rate of uptake timed. These tests demonstrated the point that lower concentration alkoxysilane consolidants have a higher absorption rate, that they all have higher absorption rates than water, and that 'old' consolidant (one that was a couple of years old) is no longer as effective as it should be when new.

Gottfried Hauff comparing the different levels of consolidant absorption in the cubes of sandstone.








This afternoon George Wheeler spoke to us on the topic 'Evaluating Performance of Consolidants; Lab Methods and Protocols'. We covered all of the main techniques for analysing stone which can be used prior to carrying out a consolidation to ensure that you fully understand your substrate. These were; Mercury Intrusion Porosymmetry, Water Vapour Transmission, Flexural Strength Tests (both '3 Point Bend Tests' and Biaxial tests), Ultrasonic Velocity, Micro-abrasion, Colourimetry, X-Ray Diffraction, X-Ray Fluorescence, Scanning Electron Microscopy, Polarising Light Microscopy, Micro-chemical testing and Conductivity tests.

Three additional basic factors that need to be assessed are the presence of biology, salts and pollution/gypsum crusts. It is important to identify the types of biology present on your stone if you wish to carry out a consolidation because removal of some or all of this growth may be necessary as an initial phase; it is necessary before this occurs to also identify the 'value' of the presence of this growth. As mentioned yesterday, you need to assess the presence of soluble salts and if it is possible (or necessary) to remove them prior to consolidation. If you do wish to remove the salts it is essential to select your method carefully; we were told of an example when a stone from a dry climate was repeatedly submerged in a water bath to remove the salts (a common technique), but the stone was not properly understood and it contained a high content of expandable clay resulting in the stone experiencing a high level of deterioration.

Gottfried Hauff finished the day with discussion on a few different consolidant-based research projects that have been carried out to understand the durability of consolidants with time and the possibility for re-treating previously consolidated areas. This session proved to be an interesting critique on research methods and the reliability of data.

Wednesday 8th June 2011; Consolidants- Alkoxysilanes

Week 9 of 12 
Module 5: Conservation Interventions and Treatments; Criteria for Selection and Implementation

We started this morning with a short presentation by Jakub D'Oubal (the Czech participant) on his involvement in a project using/testing a specific type of nanolime. The main findings of the tests he has carried out are that application by syringe was more successful than by brush, that fast carbonation was achievable and that it is possible to remove the white haze which may appear on the surface of the stone. The chemical phenolphthalein is commonly used to test for the carbonation of lime mortars and in this context can be used (prior to carbonation) to test for the depth of penetration of the nanolime in test samples. The nanolime was found to have a good level of penetration following between 2-5 applications and showed a positive consolidation (tested by ultrasound transition measurements). In his experience, the higher concentrations of nanolime can also be used as a grout.

George Wheeler started today's lectures with a summary of the topics covered yesterday. Acrylic resins and epoxy resins; these are still used but in more controlled conditions due to their low UV stability, low glass transition temperature and difficulties with penetration. The main factor in their favour is that they provide good strength increases. Inorganic consolidants; these are one of the favoured groups due to their UV stability, low viscocity and ability to work in water or alcohol (and therefore compatibility with wet stone). Their downsides include that only low concentrations of active ingredients are possible in each application and only low strength increases are possible. Reactive consolidants; these are surface consolidation techniques which consume some of the stone (probably a disadvantage) and can only be used on carbonate stones.

We then moved on to the topic of 'Alkoxysilanes' (also referred to as ethyl silicate or tetraethoxysilane- each used in a different context). George told us that the alkoxysilanes have both low viscosity and a low surface tension which are excellent characteristics for a consolidant. Water has a high surface tension meaning that the water molecules are attracted to one another causing them to 'bead up', whereas the molecules in a substance with low surface tension will be more attracted to the substrate than to other molecules of the same material hence it penetrates a larger surface area of the stone.

Ethyl silicate was synthesised in 1846 and in 1861 is is known to have been suggested, and used, as a stone consolidant for the Houses of Parliament, London. It did not have a high level of success in this case but this is thought to be due to the very poor quality stone. In the 1920s several patents were then developed for ethyl silicate and the differences in its success on sandstone and limestones were recognised. It was in the 1960s that one of the products still in use today was fully developed known as 'sandstein festiger' (sandstone strengthening agent) later to be referred to as 'Wacker OH'. By the 1980s this consolidant was being used on all different types of stone although as this was developed for sandstone it was not known how much success would be achieved on other stone types.

We briefly touched on the use of consolidants on expandable clay-bearing stones and the issues that can be faced on a stone which has a high level of contraction and expansion. As I understand it, the current belief is that the consolidant (in the case of alkoxysilanes) should be weaker than the stone and therefore expansion and contraction of the stone would cause the consolidant to break and fracture rather than the stone. If this happens you will still in some circumstances have the benefit of the stabilisation of loose grains by the additional material (even if the bonds are broken), but in other circumstances additional consolidant will need to be added and this may cause issues with closing up the porosity of the stone. There has been recent development in 'elastified ethyl silicates' with the aim of reducing the cracking of the consolidant; these are still being trialled.

In the 1980s full architectural facades were commonly consolidated, however this is now much rarer and consolidation tends to be carried out on individual elements. George does not know of evidence to say that the alterations in the charateristics of a consolidated stone should affect the surrounding stones, but an issue that may be faced is the discolouration of the consolidated stone. Dark stones tend to be more susceptible to darkening in colour following consolidation.

George finished this lecture by highlighting some of the practical problems experienced with alkoxysilanes. Alkoxysilanes are not immiscible in water and therefore a stone must be totally dry when they are applied otherwise you will have the solidification of the consolidant where it hits water and therefore blocking of the pores will occur. It is likely that this technique therefore faces some serious hurdles in countries with high levels of rainfall such as Scotland. Due to the discolouration that can occur to stone following application of a consolidant it is essential that the movement of the consolidant is well controlled to prevent ugly drips and spills discolouring surrounding untreated stone.

Gottfried Hauff joined us this afternoon and will be with us until the end of the week to add to the discussion on stone consolidation, the lecture looked at 'Structural Stone Consolidation Methods and Treatment Conditions'. We must consider extraneous factors when considering the consolidation of stone such as the presence of soluble salts. Gottfried advised that either salt extraction must come before consolidation or you must pre-consolidate the stone, then extract the salts and then carry out the full consolidation.

We discussed the depth that the consolidant needs to penetrate to to be successful, which according to Snethlage and Wendler (specific reference unknown) should be 'deeper than the mean moisture penetration depth.' This is essential because otherwise if the average rainfall penetrates the stone further than the deepest part of the consolidation you will create a stress zone which will be subject to enhanced weathering/decay. I fear that in an exposed Scottish sandstone building where there is an open porosity the rain penetrates so deep into the stone that it may be difficult to achieve this depth with a consolidant. Gottfried has recommended that I read the chapter in the book referenced yesterday 'Stone in Architecture' related to this topic.

We were shown the various techniques that can be employed for applying the consolidant to the stone including; 'flooding' which requires the capillarity of the stone to draw the consolidant in, 'poulticing' where a stone is wrapped in cellulose paper and the consolidant continuously applied to the paper so that it drains into the stone, 'immersion' which is only possible for movable elements where it is fully immersed into a bath of consolidant and finally 'vacuum impregnation' which is a new technique requiring the object to be fully sealed at its surface and then the consolidant added under a vacuum. Gottfried emphasised the need for good protection of your stone before, during and after consolidation to create the required environment for the consolidation process to be appropriate to the technique. It is possible to have some 'remigration' of the consolidant to the surface of the stone if the environment is not carefully controlled.

George Wheeler finished the day with a case study of 'Consolidating Deteriorated Marble with Alkoxysilanes at St. Trophime Cloister, Arles, France'. A wide range of consolidants were trialled on samples of a deteriorated stone similar to that found at the site and then a rigorous testing program was carried out including capillarity, water vapour transmission, micro-abrasion, ultrasonic velocity, biaxial flexure and colorimetry. The same tests were carried out on a second set of samples following time in a weathering chamber set at a low 'intensity'. There was no clear result in favour of a particular consolidant and the success of each consolidant varied with the different tests. I believe more tests will be carried out before a consolidation regime is decided upon.

Note to reader: This is an entirely new topic to me and I would particularly welcome comments or corrections on any of the notes I have made.

Tuesday 7th June 2011; Consolidation- Introduction, Water-Based Treatments and Solvent Based Treatments

Week 9 of 12 
Module 5: Conservation Interventions and Treatments; Criteria for Selection and Implementation

George Wheeler, Director of Conservation Graduate School of Architecture, Planning and Preservation Columbia University and a Conservation Consultant for several organisations, joined us today and will be with us for the next few days to discuss stone consolidation. David Odgers also rejoined us to discuss consolidation using water-based techniques.

George started by giving us a reference for a book which he said should be at the top of our reading lists; 'Stone in Architecture' edited by Siegesmund & Snethlage.

The two common aims for consolidation are to increase the strength of a deteriorated stone and to limit loses by certain forms of deterioration. Consolidants were used extensively in the UK in the '70s and '80s but their use is now much less, most likely due to the ill effects being experienced since then due to the methods used. As I understand it, the technology is moving slowly, but research is continuously being carried out and new methods are being developed and old methods improved. Consolidants are able to restrengthen certain forms of deterioration, but they will never mend stones which are flaking, scaling or spalling and other techniques would be required to save these surfaces (e.g. grouting). For this reason certain types of stone such as slates which break apart in 'sheets' cannot be consolidated.

Most types of stone are receptive to consolidation, but many different factors need to be considered when deciding on the method; chemical sensitivity, water sensitivity, porosity, pore size distribution, strength and frequency of use. For this reason initial conditions surveys are essential to allow you to characterise the substrate. Consolidants should also be selected based on the type of consolidation that you wish for them to perform; the two highlighted were by a 'depositional process' whereby the spaces between grains are filled to reduce movement and by an 'adhesive process' which creates a chemical link across the grains. Throughout history a wide variety of organic and inorganic consolidants have been used and George described the use of consolidants as a 'fashion industry' where you can see the trends for use decade to decade.

We were given a list of the properties of the ideal consolidant (which doesn't (yet) exist!) including factors such as light stable, high glass transition temperature (the temperature at which a material changes from a glassy substance to a plastic one where it becomes sticky), ease of use, compatibility with other conservation activities, limits future deterioration- the list continues.

In the second half of the morning we had a session with David Odgers on 'Water and Lime-Based Consolidation'. We discussed the 5 main types of 'inorganic' consolidants; calcium hydroxide (lime water), nanolime, barium hydroxide (baryta water), colloidal silica and calcium oxalate. I have made a few observations on the lime-based techniques below.

The lime water technique is theoretically an ideal way of re-cementing a deteriorating limestone because essentially the method reintroduces a calcium carbonate cement around loose grains. The technique works by combining a lime putty with water in the same way as you would produce a limewash, however the aim of this technique is to retain the original colour of the stone rather than producing a coating layer in the way of a limewash. The water and lime putty mixture are allowed to settle out until the liquid overburden is clear; this clear over burden is the lime water which can be siphoned off. The container must remain sealed during this process to prevent any air carbonation of the lime and it is preferable to keep the container cool because lime is more soluble in cold rather than hot water. The lime water has a concentration of c.1.4g of lime per litre and for this reason multiple applications (around 40) are necessary to produce a consolidating effect. One of the serious downsides of this technique is that you must introduce a very large quantity of water into your stone which may not be desirable.

Nanolime is one of the current 'fashions' in the consolidation industry and the technique is constantly being developed and refined. Nanolime is so called because it has particles of lime which are on the nanometre scale (1 nm = 1 thousandth of a micron). The benefits of the small particle sizes are that they have the possibility to penetrate deep into the damaged stone, they have a high reactivity and a high purity. Very old (well matured) lime putty can actually be on the nanometre scale, but it differs from the nanolime due to its water content; nanolime instead uses alcohol. The concentrations of nanolime available vary from 5g/litre to 50g/litre and it can therefore be many times more concentrated than limewater.

This afternoon George Wheeler continued with an introduction to consolidants and then looked at 'Thermoplastic & Thermosetting Organic Polymers for Consolidating Stone'. We were shown various forms of 'reactive' consolidants which work by dissolving/digesting a part of the substrate to create the consolidant such as ammonium tartrate which when added to a limestone reacts with the calcium in the stone to create calcium tartrate. George explained that many such techniques are essentially surface, rather than penetrating, consolidants.

Thermoplastic resins were described as those that dissolve in organic solvents (e.g. Paraloid), and thermosetting resins as those which once set cannot be dissolved in organic solvents (e.g. epoxy or polyester resins). George listed some of the wide range of organic materials that have been applied to stone to act as consolidants from waxes and drying oils (e.g. linseed oil) to polyethylene glycol and cyclododecane. The latter is described as being a 'sublime' so it essentially 'disappears' at room temperature making it a very useful temporary consolidant, sometimes used when a deteriorating object needs to be transported.

An aside from this lecture; David Odgers described the use of 'Sheltercoat' in his lecture on 27th May and yesterday during the lab session he applied a sheltercoat to a block of sandstone. Today he showed us the results under a microscope and you can see the results below.

Two blocks of the same stone but the one on the left has been treated with the sheltercoat.

Close-up of the sheltercoat-treated stone (left) and untreated stone (right). The images are c.25mm in width.

Monday 6th June 2011; Mosaics & Mortars Testing

Week 9 of 12 
Module 5: Conservation Interventions and Treatments; Criteria for Selection and Implementation

We were back in the classroom this afternoon, after our Study Tour, for lectures on mosaics with Thomas Roby and a follow-up mortars lab session with David Odgers.

Details to follow...

Sunday 5th June 2011; Ravenna

Week 8 of 12 

Module 5: Conservation Interventions and Treatments; Criteria for Selection and Implementation 

The Study Tour: Ravenna

We arrived in Ravenna last night and this morning visited a selection of the sites famous for their mosaics. The mosaics date from the 5th Century A.D. and are incredibly stunning in both their colours and designs. Below are a selection of photographs from the visits but they need to be seen in person to see their extent spatially and in colour and design.

The Basilica di San Vitale (with our group). 

Mosaics inside the Basilica di San Vitale.

The Mausoleo di Galla Placidia.

Close up of some of the mosaics within the Mausoleo di Galla Placidia.

An agate window within the Mausoleo di Galla Placidia.

The Baptistero degli Ortodossi (o Neoniano).

The central ceiling mosaic in the Baptistero degli Ortodossi (o Neoniano).

A crack observed in the wall of the building which goes through bricks indicating that the mortar used here was too hard; the break should run through the mortar and not the masonry.

A lime mortar present on the wall of the 

Baptistero degli Ortodossi (o Neoniano) showing the apparently typical wide joints and large aggregate. This appears to be an area of recent repointing but it ties in very well to the original mortar.

The Basilica di San Apollinare Nuovo.

The interior of the

 Basilica di San Apollinare Nuovo with mosaic wall decoration.

Many of the columns within the

 Basilica di San Apollinare Nuovo were strapped with iron which I assume indicates that the marble columns had been showing stress. This column was particularly well strapped.

On our route into and out of the town we observed this steeple on the Basilica San Giovanni Evangelista which was of the same construction as the steeple we visited on site in Parma. It was particularly surprising to see this as we had understood that this construction technique was only really used in the South of Italy where the climate was milder.

The Basilica di San Apollinare in Classe which we stopped at on our journey out of Ravenna.

Some of the mosaics within the Basilica di San Appolinare in Classe. In the enlarged image you may just about be able to make out three red lines (one running along the backs of the sheep, one running across from the hand on the right-hand side of the image and one encircling a tree third from left in the centre of the image. This technique was often used in the past (less now I believe) for indicating areas of reconstruction. We were debating which side of the line was the reconstruction but the common consensus was that the smaller areas were the original (e.g. the encircled tree) and the rest the reconstruction.


We arrived back in Rome this evening having covered 2100km since when we left last Sunday (29th May).

Saturday 4th June 2011; Venice

Week 8 of 12 

Module 5: Conservation Interventions and Treatments; Criteria for Selection and Implementation 

The Study Tour: Venice

This morning we took a boat to the Piazza San Marco where we met Paolo Pagnin again (see Friday 3rd June 2011; Venice) to discuss and visit the site he is currently working on in the Piazza; Procuratie Vecchie. We were given a presentation on the work being carried out on site by a member of Paolo's team and by the site architect. The building spans 54m along the northern side of the piazza and is 19m high. Construction began from the eastern end in 1513 and was completed at the western end in 1538; it is the oldest building in the piazza and is very unusual in that it has structural stonework which can only be found in one or two other Venetian buildings.

View of Piazza San Marco from the Canale della Giudecca.

The Procuratie Vecchie in the centre and right-hand side of the photograph.

View of  Basilica Cattedrale Patriarcale di San Marco at the eastern side of the piazza from the scaffolding on the Procuratie Vecchie, which is also visible extending along the left-hand side of this photograph.






The project currently underway is to conserve the historic facade of the structure and the architect described the aim of the work as 'to conserve the first layer of patina below the crust'. Extensive documentation has been carried out prior to the start of any work. The method being used on site for removal of the black crust (following tests) and as specified by the architect is a biological poultice which is a combination of urea, glycerine and water. The use of this technique has to be well timed because the pH of the poultice has to be controlled and kept below 10; after 10 days the pH of the solution can rise rapidly to 12. Some thicker areas of black crust are being scraped back using a scalpel as an initial stage. After the poultice is removed the surface of the stone is being brushed and sponged with water and some focussed laser cleaning is being carried out in specific areas. The facade is tied into the building by chains and iron fixings around some of the columns. Where possible these are being retained and treated with an anti-rust treatment but some are too decayed and will have to be cut through and replaced. In some areas it was possible to look into the ceiling space and observe the back of a lath and plaster ceiling. Paolo told us that on the other side is a fresco ceiling. The lath is made from a type of bamboo that can be found in the lagoon.

One of the capitals following removal of the black crust. A red-brown patina was discovered on all of the capitals at one level and it was decided that this was the desired level of cleaning. An iron tie which is attached to a chain holding the facade in to the floors is visible in this image.

A capital still in it's original state prior to cleaning.

View inside the structure into a space above a ceiling showing the lath and plaster rivets.








After the site visit we had a few hours free time to walk around the city, a couple of observations are below.

The water-side facade of a building showing the large amount of damage caused by the rising water from the constantly saturated part to the salt deposits and damaged brickwork and the almost total loss of render.

A beautiful example of the location and formation of black crusts. We have been told that black crusts develop in areas that are protected from water (rain fall) and it is quite clear here that the exposed parts of the building are white and the sheltered parts below the cornices are black. The faces must protrude just far enough that they have been washed clean and stand out in great contrast to the sheltered areas of black crust.