Fixing stone in time: Making and measuring consolidants for heritage futures

Abstract

Stone consolidants have been used in conservation practices for decades, with an increasingly interdisciplinary scientific attention to their composition and performance. This article is an ethnographic account of the process of testing a new consolidant's efficacy, drawn from fieldwork and interviews with scientists and heritage professionals involved in a European project in 2013. I illustrate, in line with prior scholarship on laboratory time, how time is a central tool of laboratory control, which must be managed to produce evidence of consolidant efficacy. Yet the ‘fast time’ of controlled experimental conditions is also suspect for those working in the field of heritage. By tracing the temporal tensions between scientific evidence making, laboratory practice and heritage practitioners’ values, I illustrate that the project of materially fixing stone in time means intervening on heritage futures.

Keywords

artificiality consolidation decay heritage stone weathering

A high proportion of the world's cultural heritage is built of stone, and it is slowly but inexorably disappearing (Doehne and Price, 2010: 1)

Buildings evolve and change. How do you propose to stop time? (Viollet-le-Duc, attributed, in Wells, 2007: 2)
What are the temporal politics of consolidating stone? In this article, I give an account of scientific interventions in stone decay through nano-consolidation, taking the reader into laboratory practices designed to imitate weathering as the passage of time. Focused on shifting perspectives on testing regimes and scientific knowledge, I explore how weathering is culturally and scientifically made into a materialisation of time, and interrogate the professional, aesthetic and implications of efforts to interfere with it. My account begins in the basement of an Italian manor, in 2013, in the city of Perugia, Italy, during fieldwork. Sitting on the back row of the dark space, I can see a man clicking through his Power Point slides, presenting the outcome of years of work to his colleagues. With me in the vaulted space are researchers, predominantly chemists, engineers and geologists. They are here at the 18-month review of their 48-month research project. I am attending with members of my project team based in Scotland that include geologists, archaeologists, and anthropologists like myself. The presenters have, over the past couple of days, talked us through their project's work, which is taking place at heritage sites across Serbia, Italy, Slovenia, Russia, Scotland and England.¹ Together, the partners on ‘The Protection of Cultural Heritage Objects with Multifunctional Advanced Material’ (HEROMAT hereafter) are working to research and design new materials for cultural heritage buildings, to protect them from decay without damaging the underlying stones or changing how they look (HEROMAT, 2012). While the project will run tests at two European sites, Dornova Manor in Slovenia and Bač fortress in Serbia, selected to be ‘case studies for two types of historical object’ (Ranogajec, 2016), the work is thought of as relevant to thousands of Europe's heritage buildings. They are considered to be ‘at risk’ (Rico, 2015), now and in the future from intensifying atmospheric pollution and climate induced rainfall. The presenter up there on the stage in Perugia openly admits that designing any material for conservation is a very big task. As a research team, they have to think about a lot of things. He lists them:
Compatibility, durability, aesthetics. [We have to get it right] in order to respect the style, the language of the original material, which can be altered by restoration. In an object is the patina formation, and we have to distinguish the interface between pathology and weather aging. As far as possible we have to respect the passage, the language of time.
Throughout this article, I present fieldwork conducted subsequently with geologists who were there that day, back in their home University and laboratories in Paisley, outside of Glasgow in Scotland. Drawing on interviews, observations and field trips, I seek to shed light on what it means to prevent decay while ‘respecting the language of time’, and the stakes involved. According to heritage professionals, the task of prevention is an urgent one, with anxieties about the intensification of weathering through climate change high on discussion agendas. Stone decay is a vast topic, the subject of poetry, aesthetics and, in more recent years, scientific study and intervention. Stone, interviewees told me, carries the ‘memory of industrialised atmospheres’ (see also Belfiore et al., 2013), marks acidifying rainfall and across European cities (Grossi and Brimblecombe, 2002; McGreevy et al., 1983), and has become a contested aesthetic (Ball et al., 2000; Eklund and Hummelt, 2013). At stake in its consolidation for project members here in Perugia is the ‘preservation of the material testimony’. It is their hope that ‘the use of new conservation materials and techniques gives the cultural assets a chance to last longer in order to be preserved for future generations (HEROMAT, 2015). Promotional material for the project ties the application of these new ‘advanced materials’ to the improved condition of cultural heritage, and their long-term ‘resistance’ to environmental influences (HEROMAT, 2014, translated from Slovenian). The achievement of this long-term vision, however, sits uneasily with existing philosophies and structures of governance over those ‘historic structures’. In the words of one of HEROMAT's geochemists, ‘despite you being the best chemist in the world, people might not want to use [the consolidant], or they need other things to be considered’ (Interview 5). My ethnography, as part of the interdisciplinary research project Materiality Authenticity and Value in the Historic Environment (AHRC AH/K006002/1) was about how these ‘other’ considerations met the materialist concerns of conservation. Over the course of six months, I followed work that tested the nanotechnological consolidants that, if applied to stone and other geomaterials like brick, mortar and concrete,² would provide the desired ‘resistance’ to decay and erosion of the elements. The work was part of a broader enquiry into questions of value and authenticity in the conservation of historic buildings, and the role of scientific research in heritage (Douglas-Jones et al., 2016; Jones and Yarrow, 2022).

To explore the temporal politics of consolidation, I examine the making of time in laboratories that weather and test consolidated stone and geomaterials. Two questions drive the article: first, how is weathering culturally and scientifically made into a materialisation of time, and second, what are the implications of efforts, such as consolidation, to arrest or slow weathering's effects? I address the first by introducing the problem of stone decay and consolidation as a means of remediating it, before moving the analysis into the lab. Here, we explore the broader, second question, since an encounter with practices of artificial weathering prompts questions about temporal agency, scientific knowledge, its place in heritage practices. At the same time, it brings the philosophical, policy and financial contexts in which consolidation products are being developed into relief, sharpening the political stakes of laboratory labours.

Problematizing stone decay

The study of stone decay is a multidisciplinary field, the concern of chemistry and town planning, history, archaeology, geology, earth sciences, engineering and more (Hirsenberger et al. 2019; Hughes 2017; Smith et al. 2008). As such, what it is and what it means vary according to disciplinary perspective, emphasis and terminology, as scholars distinguish degradation from damage, deterioration from decay (Vergès-Belmin 2008). Where disciplines and forms of expertise encounter one another (usually around a case) contestations arise about what, if anything, to do about it. Concerned with understanding the mechanisms of a process that varies by geography, locale and stone type, different patterns of environmental decay are commonly encapsulated under the term ‘weathering’ (Douglas-Jones et al. 2016). The mechanisms are well researched and, to some degree understood: when stone is exposed to the environment, in the form of water, salts, polluting agents, microbiological growth, wind, temperature, physical wear-and-tear form humans (Smith and Turkington 2004) it ‘weathers’. Yet quite how stone decay unfolds remains the subject of considerable research: it may be nonlinear (Viles, 2005), and while stone carries the cultural symbolism of durability, seen to accomplish a ‘measure of stasis’ (Gieryn, 2002: 35, see also Cohen 2014: iii), different types of stone are differently vulnerable to decay (Steiger et al. 2010). Since the turn of the century, materials science has changed the opportunities available to researchers and practitioners for understanding stone and its interaction with weathering elements, with a huge growth in papers giving ‘special attention’ to nanomaterials over the past 20 years (David et al., 2020). Nanoparticles, matter between 1 and 100 nanometres across, are described as a ‘key enabling technology of the 21st century’ (Stylianakis, 2023). For conservation science, they are part of a suite of technologies that through which ‘the nature of historic buildings and monuments, and their dynamic relations with their physical environments, [are] altered to some degree, whether directly or indirectly’ (Douglas-Jones et al. 2016: 824).

These ‘dynamic relations’ are central to HEROMAT's focus, since the project's research was aimed at buildings exposed to the elements, otherwise known as immovable cultural heritage assets. What does it mean to intervene on these dynamic relations, to ‘fix’ (Bartolini 2020: 377) or ‘make fast’ (Jones and Yarrow 2022: 167) objects of conservational interest? Why is this desirable? This is a question HEROMAT shares with scholarship across the centuries. In Perugia, we heard the explicit desire to preserve ‘the material testimony’ of immoveable built heritage, the purpose of the research and its moral justification. As such, in this article, I regard weathering as a temporal concept, situated within a field – heritage – itself replete with material time-making. Yet there are novel temporal politics on the horizon. As HEROMAT's scientists work to find long lasting, invisible consolidants that will protect buildings ‘from the disintegrating effects of nature's forces’ (HEROMAT 2012), the field of heritage is trying to come to terms with its own ‘loss aversion’ (Holtorf, 2015). Under the umbrella of heritage futures, during the decade during which HEROMAT takes place, loss shifts from being a core aversion to being contemplated as a means of embracing ‘relinquishment’ over restoration, ‘curated decay’ (DeSilvey, 2017) over curated preservation. Reorienting the field to the long-known inevitability of loss, its politics and potential (DeSilvey and Harrison, 2020: 1), parts of the heritage field are seeking to address the times in which buildings and material, particularly those that would constitute ‘immoveable’, exist. These approaches, writes DeSilvey, ‘aim to work with change rather than arrest or reverse it’ (DeSilvey, 2017: 179), pushing for a shift from ‘managed decline to adaptive release’ (DeSilvey et al., 2021: 418).

Prior to this turn towards loss, the significance of intervening on ‘heritage futures’ (Harrison et al. 2020) has long been part of debates in conservation philosophy. As Jones and Yarrow summarise, in the nineteenth century, some preferred restoring buildings as they decayed, others preferred a less interventionist approach (Jones and Yarrow 2022). Campaigns for the latter insisted on the inherent value of decay, whether phrased as the ‘profound, atmospheric presence’ (Jones and Yarrow 2022: 166) of Ruskins’ golden stain of time’ (1880: § 10) or Riegel's ‘age value’ (1996[1902]: 58) (cited in Jones and Yarrow 2022: 167). Heritage consultant Wells’ analysis traces the incorporation, in the 33 years between the Athens Charter of 1931 and Venice Charter of 1964, of scientific research as a tool in the fight against decay, culminating in the 1964 declaration that: ‘the conservation and restoration of monuments must have recourse to all sciences and techniques which can contribute to the study and safeguarding of the architectural heritage’ (2007: 9, emphases added).

Calls on scientific knowledge for heritage purposes are today intensified by climate crises. While it is accepted that heritage sites over which organisations have stewardship ‘often consist of complex systems with multiple physical and chemical processes acting concurrently’ (Cutajar et al., 2019: 1), the speed at which weathering happens, particularly through rain and wind patterns, is changing. In Scotland, the concern is around present and projected increases in rainfall (Sesana et al., 2018, 2020)³. Following the declaration of climate emergency in Scotland in 2019, Historic Environment Scotland issued a range of policies and documents⁴ concerned with climate and its impacts on the historic environment, noting that change, whether to ‘temperature, rainfall, sunshine, snowfall [or] wind’ [ …] ‘does not have to be extreme to have a negative impact on our operations’ (HES 2020: 16). As a European research project, with intervention sites in Slovenia and Serbia, HEROMAT was operating across countries and a range of heritage jurisdictions. However, the HES report makes visible how threats to stone exceed any given site or monument. And in the process, the climate crisis, as another temporal horizon for understanding and intervening on stone decay through consolidation, has slipped into view.

On consolidation

Stone consolidation is ‘used to improve the cohesion of weathered stone when serious decay patterns and in-depth cohesion loss are present’ (Ferreira et al., 2008: 39). Doehne and Price's (2010) definition offers a simple overview of the practice: For stone ‘severely weakened by decay’, consolidation might restore strength, and ‘one might hope to make the stone at least as strong as it was originally, so it might resist further decay, but even the strength to resist the battering of the wind or the wing of a bird may be enough to prolong survival’ (Price, 2010: 35). Using any material in a building changes its life, and how weathering impacts it. As Smith et al. put it, ‘placing stone in a building does not cut it off from natural patterns of weathering; instead it superimposes on top of natural processes, new, additional, sets of conditions and factors that interact in complex and often unpredictable ways to produce new patterns and rates of decay’ (2008: 442). Scholars following a geologic turn towards the deep-time character of stone observe the presence of ‘seemingly incompatible temporal orders’ (Farrier, on Halperin, 2014: 4, see also Reinert, forthcoming), present here too, as the deeper times of building materials – their geological formations and origins – are placed alongside architectural and skills-based social histories. But human interventions to help stone ‘resist further decay’ are legible too. Conservator Elizabeth Garrod writes that historically, ‘waxes and linseed oil were used as water repellents’ (2001: np), with the idea that keeping water– as a key driver of stone decay –away ‘halts decay and prolongs life’ (2001: np). However, Garrod's hypothetical scenario of a consolidation intervention also shows what can go wrong:
A decade of extremely wet weather interspersed with unusually low temperatures heightens the natural weathering. The atmospheric pollutant, sulphur dioxide, combines with the calcium carbonate in the stone and creates a hard gypsum layer covering the surface of the stone. This means that moisture inside the stone cannot escape and salts may crystallise behind this hard layer and eventually cause spalling, which leaves a weak exposed surface, more vulnerable to natural weathering. The owners of the building notice the problem but choose the wrong type of treatment, perhaps a water repellent treatment that does not breathe. It does not penetrate any further than the surface and the result is a hard, impervious outer surface like the gypsum. Ultimately the same problem arises as before (Garrod, 2001).
To avoid treatments that accelerate, rather than prevent, decay, heritage professionals work with material scientists towards the creation of consolidants specifically intended for buildings conservation. This work takes place in an arena where knowledge of materials, their behaviour and performance is already richly contested. In 1997, for example, the Director the Technical Conservation, Research and Education Division of Historic Scotland reflected that while ‘scientific research has provided increased understanding of the complex processes of decay’, these ‘advances in knowledge often create dilemmas for practitioners as they can directly challenge previously published statements on the philosophy and ethics of conservation work’ (Maxwell 1997: iii). Broader questions arise, as practitioners ask themselves which changes reflecting the passage of time, and patination of surface, cannot happen? If ‘age value’ (Riegl 1996[1902]) is reflected – in some heritage philosophies – by decay itself, then what time occurs to and for stone if it chemically cannot host biological growth?

Reviewing the properties of nano-consolidants, Sierra-Fernandez and colleagues justify the considerable research that has gone into by explaining that ‘consolidation treatments are the most risky conservation actions due to their irreversibility and the likeliness to cause undesired effects (Sierra-Fernandez et al., 2017: 2, emphases added).⁵ Intervention might cause the loss, they write, of that which was to be preserved (Sierra-Fernandez et al., 2017: 2). This sense of riskiness in a risk-averse field can, in practice, lead to frustration for scientists. As the conservation material scientists Doehne and Price note, a ‘scientist may be convinced of the validity and importance of his or her results, but there are others to be convinced before the results can impact on conservation policy’ (Doehne and Price, 2010: 54). At stake is the problem of ‘new’ knowledge, scientifically derived, for a discipline committed, in the words of one interviewee, to ‘keeping things fundamentally the same’.

Consolidation then, is the application of one substance onto the surface of another, usually with the intent of having that substance seep into and thereby create a barrier between the (original) material and the forces that weather it. ‘It all sounds so easy’, Doehne and Price comment, before launching into a list of challenges: the product must penetrate the stone, bind and secure it; it might additionally repel water and reduce damage from salts, thus preventing further decay. There are conditions that must be met for a product to be viable: cost, environmental, effectiveness, durability, compatibility, generalisability and invisibility (Doehne and Price, 2010: 35). Only a paragraph later, therefore, do they acknowledge that ‘it sounds absurd to attempt the task. It is like trying to find one pill that will cure all the diseases known to humankind. But that has not’, they say, ‘hindered the search for an all-singing, all-dancing stone consolidant-cum preservative’ (Doehne and Price, 2010: 35).

Within HEROMAT, the search for such an ‘all-singing’ material has continued. Funded under the European FP7 scheme between 2011 and 2015, HEROMAT was one of several projects designed to be part of creating materials to solve specific problems to do with the decay of ‘heritage’ objects⁶. HEROMAT's additional challenge was to create an environmentally friendly material with ‘value added functions’, namely, consolidation, self-cleaning and anti-microbial properties (Ranogajec, 2016). ‘It is anticipated’, announced the project's launch brochure, ‘that the new materials will protect against weathering and erosion, and preserve appearance but without affecting the way that moisture moves through the building, allowing historic buildings to ‘breathe’ and control biological growth on the surface.’ In later publications, documenting the resulting ‘multifunctional advanced materials’, researchers on the project describe the project's desired contribution ‘an efficient and long-lasting solution for the prevention of degradation, keeping the authenticity, functionality and the aesthetic appearance of the cultural assets and remaining [sic] their socio-economic benefits’ (Ranogajec et al. 2012). In these statements, preventing decay is a technical problem to be solved for cultural reasons. The aesthetics of a building appear through a nod towards the preservation of appearance, a separation which initially seems to actively discard an aesthetic of decay yet to come, or the politics of a ‘protection’ that reduces or prevents weathering as evidence of the passage of time.

The first step in my enquiry into how scientific times intersect those of heritage practice is to enter the laboratory where the testing of nanotechnological consolidants is being done. By recounting stories of the laboratory practices that give rise to knowledge about how consolidating ‘new materials’ operate, I lay out some of the contrasting temporalities and visions at work in making consolidants for heritage buildings, and suggest that the politics of conservation science prompts broader questions about how the multiple times of stone should be ‘used, lived and valued’ (Temporal Belongings, 2020).

Artificial weathering: lithomimesis and making realistic decay

We are in the lab on campus in Paisley, Scotland. It is a bright, artificially lit square space, with low ceilings, small windows and a large central workbench. Standing between the bench and the array of machines plugged into walls all around the edges are the three of us – John, the geologist, Bill the technician and me, the ethnographer. It is March, 2013, and here in University of the West of Scotland, partner in HEROMAT, we are tasked with analysing samples provided by colleagues in Serbia. The samples have arrived by registered post in a large cardboard box filled with sample bags, which sits on the Lab's central bench, along with the geologist's notes on the procedures that must be undertaken. ‘Having samples allows us to experiment on them’ he explains kindly to me, gently sorting the small bags of mortar, concrete and brick. Initially we discuss whether the samples have been drawn from the actual buildings under study, Dornova Manor in Serbia and Bač Fortress in Slovenia. This would be good for scientific work, and not so good for the buildings, if they have been drilled for samples. The possibility of sampling from heritage buildings strikes the technician as a bit worrisome: he is uneasy about lopping bits off them, even if for the purposes of experiment aimed at preservation. However, what we have on the table in front of us is not sampling extractivism. In a prior round of research, the geologist received original samples from the project's ‘priceless’ trial buildings (Legan et al., 2016: 1), and sent back data ‘characterising’ the materials. This characterization led to the creation of ‘materially identical replicas’ upon which the project's range of consolidates could be tested – a kind of lithomimesis. As HEROMAT's reporting documents note, researchers ‘produced model substrates identical enough to historic materials to be perfectly suitable for testing of newly developed materials (consolidants and protective coatings) and accordingly it ensures a safe application of these materials to the selected historical sites’ (2014: 12). These lithomimetic objects are the ‘material substrates’ now sitting on the table in front of us in Paisley, standing in for the materials upon which the new products may someday be used. With decay as a threat, creating accurate weathering both of test substrates and of consolidated samples becomes a goal.

Imitation of geomaterials as samples for the testing of products is relatively recent. In interviews, conservation practitioners remarked that previously ‘we could only rely on an industry which produced a lot of products for other purposes. We could only take what could be suitable for us, but it was not produced for us. Something is changing’. They are not alone in this observation. Historians of chemistry Bensaude-Vincent and Stengers observe that part of this change is that materials are now made to solve specific problems: ‘one develops an “informed material” in the sense that the material structure becomes richer and richer in information’ (1996: 206). HEROMAT, and projects like it, are part of this shift. In the years after my fieldwork, the tea published research articles detailing the protective coating developed as a ‘nanocomposite based on anionic clay minerals (layered double hydroxides – LHDs) with incorporated Ti0 photocatalyst’ (Ranogajec et al., 2018: 1698) and its performance on the buildings of HEROMAT's study after three patient years. In the Lab, this coating – or an early version of it – has been applied the samples in the box. The informational richness of both samples and their coatings is deepened by work like John's, and the work we are about to carry out. First, we read the documents accompanying the samples, learning that some have been treated with the new consolidants, some not. Bill and John will be examining how effective the treatments have been, since all 30 samples have been exposed to what is known as artificial weathering in the Lab.

The term artificial weathering refers either to a deliberate practice of aging materials to look as though they are older, or a practice used in laboratories to test the likely performance of materials over time. In the former meaning, one might age ‘fresh’ stone (Griswold and Uricheck, 1998) by adding colour or ‘microbial rock varnish’ (Pope et al., 2002: 222), deliberately patinating for aesthetic purposes. The latter meaning, relevant to John, Bill and me, sees scientists ‘reproducing and accelerating environmental weathering processes occurring in the field’ (Franzoni et al., 2013: e86) on test materials. It is not only the substrates, then, that are imitated: it is also the processes that damage and age stone that are mimicked, at speed.

The stone samples with us now in Paisley have, following a chemical analysis of the make-up of the original materials, been deliberately manufactured as samples – or substrates – for our use. But ensuring realistic decay means artificially weathering the sample prior to its treatment with consolidant. This is because ‘the effectiveness of … consolidates significantly depends on the weathering level of the tested stone’ (Franzoni et al., 2013). Since such ‘environmentally weathered stone samples are rarely available in sufficient quantity and with suitably constant characteristics’, it has become necessary to develop ‘methods for artificial weathering of stone’ (Franzoni et al., 2013). HEROMAT's reporting documents detail the ‘simulation of degradation’, carried out through SO2 weathering of ‘20 cycles’, as well as exposure to microorganisms (HEROMAT 2016: 11).

As we stand looking at them in their unremarkable packaging, the geologist explains to me ‘To make experimental materials more relevant, they can’t be pristine. The stone is aged: its surface is 100 years of modifications, thousands of wet/dry events for a hundred years’. A ‘wet/dry’ event is one of a number of key weathering forces that act on the surface of stone, with greater efficacy on ‘cut’ stone, such as that used in building construction. In addition to rain and drying, wind, sunlight, temperature and microbial forces all contribute to visible and invisible ‘weathering’. The lab from which the samples have come has tried imitating the passage of time, but there are limits. As the lab technician, Bill notes,
We [in the project] should produce recognisable, realistic damage. Nothing weird that doesn’t appear on a real building. We should replicate real conditions, but it never really does: in reality you just don’t go from −20 [degrees] to +20 [degrees] in a day.
Bill remarks that you might have it over a week, it is Scotland after all. We all laugh, as the Glaswegian weather does indeed seem to cover several seasons in a single day, and John replies: ‘Yes, but here they accelerate it considerably, 300 times over 6 months, on 3–4 cycles a day’. To create artificial weathering then, ‘real’ conditions happen in ‘unreal’ time. In a video covering HEROMAT's work, ‘New Skin for Old Stones’ the viewing public learns researchers have been subjecting them to sulphur dioxide, exposing them to salt and carbon dioxide, attacking them with polluting microbiological agents and putting them through lots of freeze-thaw cycles (Euronews, 2013). ‘There is nowhere on earth’, John tells me, as he sorts the samples, ‘that stones would go through the heat cold extremes that these samples have subjected to’.

While long-term studies of the effects of consolidation on stone do exist, we cannot wait 30 to 40 years to see whether the consolidant being developed in the project is efficacious. The research has to ‘adapt and reconfigure natural processes’ in the laboratory, to ‘suit the spatio-temporal requirements of scientists’ (Knorr Cetina, 1999: 27) – and the market. Adjust time we must, for the kind of ageing these stones require far exceeds the funding duration of any European funded project. Our activities are paradigmatic of what Knorr Cetina describes as the ways scientists resist the natural tendencies and properties of an object: we have before us ‘transformed and partial versions’ of our object, it is ‘extracted’ from its environment, and we are dispensing ‘with natural cycles of occurrence and make events happen frequently enough for continuous study’ (Knorr Cetina, 1999: 27, see also Knorr Cetina, 1992). Accelerating cycles of freezing and thawing compresses weeks into hours, years into months. At the other end of this artificially accelerated time lies a future, in which the efficacy of consolidants can be seen in the present.

To see how well the consolidants slow the effects of (artificial) weathering events, we turn to the machines surrounding us in the Lab. We will ‘impregnate’ the samples with yellow fluorescent resin, a colour that will later, under the scanning electron microscope (SEM), show the sample's porosity and structure. John and Bill create smooth discs containing the samples, work specified down to the micron on a lathe. As we work, putting the samples under pressure and smoothing their surfaces, we discuss standards and protocols for artificial weathering, or accelerated weathering as it is officially known. John, however remains skeptical that the mimicry is sufficient to model how the stone of actual heritage buildings will respond over time:
Surfaces have a memory of 100 years, of coal burning society, atmospheric pollutants, they may even contain the products of reactions. They have memories of stone cleaning events, whether that was chemical or what, it changed the internal structure, it physically modified them. … Aged stone behaves extremely differently to pristine stone. It's actually a totally different thing, a completely utterly different thing.
His comments make me look again at the Slovenian samples that have travelled here to Paisley. To that point I had followed the linearity of consolidant ambition, in which an object of the past, protected from the cyclical (weathering) time of the present, is preserved for the future. But in response to John's unease, his contrast between stones with memories and stones that are pristine, perhaps we need another story. What we are doing emerges not only from a commitment to a future, but a question of temporal density in the present: How to trick a test stone into behaving as though it has lived a long life already?

Anthropologist Felix Ringel offers – as contrast with linear, circular or patterned time – a theorisation of ‘practices that manipulate, coordinate, structure or reorder knowledge about temporal processes’…. and ‘work … actually done on time’ (2016: 25). This he calls ‘tricking’ time, focusing in on the agency required to ‘trick’ the future. I suggest that what our work in the Laboratory shares with time tricking is a concern with crisis and acceleration, and a curiosity about ‘temporal agency’ (Morosanu and Ringel, 2016: 18). Will our work of accelerated weathering prevent the crisis of accelerating stone decay? Is the combination a lithomimetic substrate, an imitated surface memory, and an artificially weathered future, a successful trick?

Seeing inside: Scanning electron microscopy and optical petrography

Let us return to this key site of temporal agency, the Lab. Weeks later, I follow John into the corridors of the University housing the SEM. Here, through petrographic observation, we will look for traces of how this speedy time has advanced decay, or been slowed by the new consolidants. Time in the SEM room must be booked: this is an expensive machine, hired out commercially by the university. Unlike glass lens-based microscopes, SEMs use high energy electrons, passed through electromagnetic lenses, to produce vastly magnified images of samples. Since their invention in the 1950s, they have become a key tool for the material sciences for their high resolution. Now used across fields from quality control to forensics, and increasingly in stone conservation, where a ‘fundamental question…. is simply: ‘what is this?’ (Hughes 2017:137). Compositional information about a sample becomes available to the analyst by means of atomic contrast, another separation in observation (Hughes, pers. comm). To work this artificial eye that can see the effects of artificial time one's vision must be skilled (Grassini, 2007). As we set up, John tells me it always takes him a while to get back into practicing how to operate the university's machine.

I sit behind John as he works, as manipulating the machine requires him to scoot back and forth between sample and screen on a wheeled chair. I make pages of notes but in the room, I struggle to follow the relationship between what I see on the screen and John's narration of what the machine is making visible. He clicks around on parts of the vastly magnified sample, lost in a sea of mineral acronyms and corresponding graphs. In my field notebook I write that the machine produces a dim image, and in response, John mutters ‘No, that's dreadful!’. In the years to come, John's work here will travel to project meetings and conferences reporting on efficacy of the consolidants, about whether they have had a protective effect on the samples to which they have been applied. His expertise is needed because the verifiability of consolidant efficacy lies at a level inaccessible to the human eye. The images and reports knowledge will be discussed in the project, eventually emerging in academic publications. What I gradually come to realise by sitting alongside him, watching as he transfers images from the software into his own files, is that we are not looking at what the project has called a ‘new skin’ for stones at all. It is inside them.

In the early 1990s, researchers complained that ‘[l]ittle attention has been given to the distribution of consolidants within stone at the microscopic level….. Many authors have been content simply to state that a treatment “lines the pores”’ (Doehne and Price 2010: 39). Others have described a ‘supporting corset’ model, ‘consisting of an impermeable layer that coats and protects the internal surfaces of the stone, while imparting mechanical strength’ (Sasse and Honsinger, 1991, cited in Doehne and Price 2010: 39). Others still lamented that little was known about ‘the bonding, if any, that takes place between a consolidant and the substrate, and much is left to chemical intuition’ (Doehne and Price 2010: 39). The situation is considerably different now. With the advent of nanoconsolidants and close studies of how consolidants behave when applied to different types of geomaterials, ‘the use of nanomaterials in the process of conservation and maintenance of stone masonries may be considered one of the greatest contributions of nanotechnology in the last decades’ (Becerra et al. 2021: 1324), with a significant increase in publications, papers and presentations since 2013 (Becerra et al. 2021: 1325).

The SEM allows me, sitting in Scotland with John, to see at very high levels of detail how and whether HEROMAT's test products are detectable and assess their efficacy. The work thus enacts the hope that, by imposing artificial weathering on artificial substrates, our time tricking has indeed been successful, it has brought into the present, as observable, the future passage of time. The data produced depends on the trick's sufficiency, as time tricking is the closest we can get to see how the consolidants will act as protectors in unknown futures, fixing the condition of even damaged stone in a perpetual present. The question remains: even with this evidence, will the consolidants be used?

Perceiving consolidants

In my broader research, I talked with heritage professionals and conservation specialists, many of whom expressed hesitancy about so-called ‘new materials’ such as those under development in HEROMAT. Few said they would use a ‘new’ consolidant. ‘Not until at least ten years, probably more’, stated Clara, an Edinburgh buildings specialist. Her timeframes are long in terms of product development, but short when it comes to lives of buildings. Clara worries about what actually goes into consolidants, and what they will do to the surfaces to which they are applied. During an interview, as we discussed what different consolidation techniques did to materials, I asked her ‘do you think it changes what the stone is, if it's got this stuff added?’ Clara:
Yes, of course it does. I guess, for the purists, but not necessarily for the public.
RDJ:
What would the ‘purists’ see that the public wouldn’t?
Clara:
Well, they might feel that you’re isolating the artefact from the processes that created it. You know, age and environment and the conditions around it brought it to where it is now and how dare you stop it moving? But then, when do you stop holding it up?
Clara's comments echo the current debates within heritage, and raise the question of who and what counts as ‘purity’ here. Consolidants enable artefacts to remain in situ, keeping heritage buildings available to public view, in their ‘environments’. Unlike objects that can be placed in controlled environments – temperature and humidity held constant – buildings continue to face weather, and human produced pollutants (Belfiore et al., 2013). Clara reflects that consolidation changes how stone responds to ‘the conditions around it’, and she asks rhetorically: ‘how dare you stop it moving?’

This is where the relationship between conservation professionals, managing time beyond the present, and viewing publics enters. I spoke with materials scientists throughout the research, who agreed that the built heritage was not just about the ‘structure’ but the environment: ‘you can’t isolate the structure on its own’, said Simon, a materials scientist who consulted regularly for heritage organisations: ‘you have to look at it within the environment it serves’. When I asked him the same question as I asked Clara, Simon observed that who sees matters:
If something has been treated, say with a polymer, only the materials scientist will see that a material has been altered. The visitor will not see ‘behind’ it, they see it at a point in time, and that is all. A material scientist will see a material that has been altered, that will change in time. And the intervention will have an impact on that rate of change.
Simon's approach was less ambivalent than Clara's: since it was ‘only a materials scientist’ who would be able to observe any change to the materials. Not equipped with SEMs, there is no way for a visitor to know about any chemical change to the make-up of the stone: they see it ‘at a point in time’. In what way does knowing matter?

This returns us to debates within on the place of scientific work in heritage, specifically the relationship between consolidation and its role in service to materials as markers of authenticity. Interventions that aim to preserve geomaterials are desired in part through the philosophical position that ‘[a]n object can only ‘bear witness’ to the true nature of the past if its physical fabric remains unchanged’ (Wells 2007: 9). As such, the project's aim to develop its ‘long-lasting solution for the prevention of degradation, keeping the authenticity, functionality and the aesthetic appearance of the cultural assets’ (Ranogajec 2012: 255) belongs to a material-centric universe, in which to retain this ‘physical fabric’, consolidants are studied at nanoscales, to see how well they ‘isolate’ stone and geomaterials from the environment. In other words, how well they fix stone in time.

New maturities of control

If laboratory techniques makes it possible to trick time, and laboratory instruments make it possible to see the efficacy of those tricks, how does the experimental temporal setting handle ideas of ‘real’ weathering time and its passage? Late in the Materality, Authenticity and Value project, we hold a workshop in a hotel on Scotland's west coast. We have convened over 20 local conservation specialists and scientists we have worked with, most of whom are practicing professionals in the sector. Over the course of the day, discussion shifts to what happens in laboratories to generate consolidants, and the participants at this workshop develop a critique that the Lab, as a space and set of practices, is too controlled for making reliable knowledge about how consolidants will perform:
The problem is you’ll develop something using sort of a fairly standard scientific evaluation approach under controlled conditions and then you’ve got the dynamic variability in the real world…
This ‘dynamic variability’ is a recognised problem for those working to establish knowledge in materials science, in particular, research into materials failures. How materials will degrade over time, and how various environments affect their future reliability and performance, has led to significant research, standards and products for testing the futures of materials. STS scholar, Andrew Barry, writing of the testing of train track metals, writes that, ‘laboratory simulations are extraordinarily inexact. Tracks in laboratories can never be subjected to the same range of temperature variations, surface contamination and stress’ (2005: 93). John's comments above resonate strongly, although his critique is that the laboratory is sometimes too extreme. On our table at the workshop, we talk about the different kinds of ‘control’ that one can, and should, exert during laboratory testing. Martha:
In experimental circumstances we might use aggressive salts to accelerate decay. NaCl, CaCO₃ are common. But they don’t give you big, impressive data.
Ben:
Yes, the solution has bigger impact on pore structure, but the temperature: you can’t replicate the site in the lab.
Martha:
You can learn processes of the mechanism, so if you put stone with moisture and salt and cycle, it’ll break down: that gives you a general level of understanding. But if you take it out of the lab to a building, the stone [there] is aged, there is render, mortar. That's my 2p worth: the whole mechanics changes.
Ben:
Well, that's the temptation: if you’re only in the lab, with a white coat on, you forget what's going on. You have nice machines. You step away from the reality of the situation. You get a data set, it is beautiful rather than explicit. You always have to question yourself. I am using this salt, is it too much? Is it realistic? If not, why use it? What is your rationale? You have to go through these questions.
Martha:
We still have BRE⁷ standard durability, and to get it you use a very high concentrate of sodium sulphate. That is not something you would ever get in reality, yet people buy stone on the basis of that test. Yes. You’ve got to be very disciplined.
This discussion adds a new dimension: what Martha is referring to as ‘discipline’ keeps the scientific experiment tied to a ‘reality’ beyond the lab, known to the scientist. Salts that produce significant scientific results may not come from a fair time tricking - the data set is ‘beautiful’ rather than ‘explicit’. Martha and Ben's concern with ‘realistic’ decay returns us to the ‘specific kind of knowledge’ (Knorr Cetina 1999: 27) sought about the products they are testing, and the worlds they are managed within. This is not a durability test of car paint, pipe metal or cable plastics. The accountabilities are not primarily product safety, but the durability of the ‘cultural assets’ HEROMAT is tasked with protecting. While we have seen how consolidants, and their temporal politics are ever richer in information, heritage objects are already very information rich (Barry 2005). Indeed, it is the significance of heritage objects that is both the reason for research into consolidants, and hesitancy about their use. As Clara made evident above, there is considerable wariness about ‘scientific fixes’, as practitioners have spent time dealing with the consequences of earlier solutions (Ginnel 2010[1996], Jones and Yarrow 2022: 169–170, 183–184).⁸ While the funding imperative for HEROMAT is to produce a commercially viable new product, and the evidence of its efficacy, those at whom the product is aimed operate with quite different timeframes in mind. In this case, ‘evidence’ does not always translate. Discussing the project's ambitions with a conservator in Scotland, we asked what it would take for her to consider the product. How much reassurance would she need to have? ‘Huge amounts’, she replied – and my scientist colleague asked her to quantify what that meant: ‘I’d like to see, probably, it be in place at every other heritage organization for at least the last ten years or something’. The orientation of the field is towards the tried and tested, the evidence of generations of experience, ‘We wouldn’t just sort of say, oh, that's new, let's try that’.

Throughout this work, I observed different ways of managing the temporality of evidence. Hesitation – the desire for not just scientific evidence but collegial testing and word-of-mouth trust – was incorporated into HEROMAT. Scientists recognised practitioners’ desire for precedence of use, incorporating in their research a ‘decision-tool’ that considers ‘peer recommendation’: ‘basically, stakeholders may simply like to know if past experiences exist or not, and if they do exist, what are these experiences’ (Turk et al. 2019: 51). One practitioner calls for the union of ‘anecdotal evidence and the knowledge of practitioners’ in order to ‘marry practitioner knowledge to studies of material properties’ (Kennedy 2016 : 215), and there are calls for far deeper training and communication between ‘disciplines in conservation and a development of the theory of conservation science by practicing scientists’ (Hughes 2017: 143). Yet there remains the conditionality of material science, the scientific relation to the past as being one of rejection, a 'rectification' of knowledge (Bachelard 1984 [1934] 297 in Rheinberger 2012: 110). In short, advance in scientific work depends on change over time, not fixity. Just over ten years ago, Doehne and Price pointed to ‘signs of a new maturity’ in stone conservation, resulting from ‘an awareness of the unintended consequences of some earlier interventions’ (2010: 79–80). They indicate ‘caution’ and an ‘incremental approach’ in the current generation, with less likelihood of ‘heavy-handed use of biocides, waterproofing agents and consolidants’ (Doehne and Price 2010: 80), practice turning more towards ‘careful documentation, monitoring, regular maintenance, control of moisture, selective use of waterproofing agents and consolidants, stone replacement, and the design of minimally invasive treatments’ (2010: 80).⁹ Incrementality sounds considerably closer to contemporary descriptions of all the considerations that conservation practitioners already balance as they seek to ‘stabilise’ the ‘unruly forces of erosion and deterioration, as well as complex histories of modification and former campaigns of conservation’ (Jones and Yarrow 2022: 184). Here, for practitioners, there are not games of time-tricking. Instead, a skilled working-with, in perhaps a growing acceptance of impermanence.

Stone time and lab time

At the outset, I sought to better understand the temporal politics of consolidating stone by exploring how weathering is culturally and scientifically made into a materialisation of time. Stone time is produced by human decisions to use materials in buildings, subjecting them to new forms of weathering. The interventions described in this article are oriented towards a future in which decay is slowed or stopped, through work that takes place in labs. However, we have seen how weathering is already part of cultural frameworks tasked with managing heritage futures, and how heritage philosophies themselves constitute relationships to the passage of time. For inheritors of the romantic movement, weathering is already seen and valued as time's material trace (Jones and Yarrow 2022: 167). This contextualises consolidation as a practice as belonging to the contested culture of conservation of the now, both revealing and constituting how national and European frameworks direct funds aligned to heritage philosophies that foreground the preservation of stone and other geo-materials. For conservation practitioners who must daily ‘negotiate the fine balance between decay and intervention’ (Jones and Yarrow 2022: 171), novel research into nanoconsolidants is occurring in Clara's gap between ‘how dare you stop it moving’ and ‘when do you stop holding it up’?

This is where my argument shifts to the implications of efforts like consolidation, to arrest or slow weathering's effects. When scientific work is enrolled in creating products that uphold these philosophies, laboratory labours intersect both times of the market and times of climate. To catch a glimpse of market time, we might return to Perugia, to the Power Points and conference with which I started this article. There is a rustle to the side of the presentation, and some murmuring. It seems one of the slides is not ready for view, it is in the slide deck by mistake. It contains images of how the consolidant will enter the pores of stones, and chemical formulas for the consolidants which have proven to resist key forces of decay. The image, and its surrounding equations, make the consolidant's language of time visible. Originating in the lab, this language is a competitive advantage, something ‘not ready’ for market, it is too soon for its formula to enter the circulation of capital. It is a small error; we move on quickly. But it reminds us that the temporal labour in the lab, providing evidence of likely performance over (accelerated) time, is in the service of ‘materials adapted to industrial demands’ (Bensaude-Vincent and Stengers 1996: 206). As for the presence of climate times within decay-prevention-oriented science, when geomaterials are put through accelerated and artificial weathering, the question arises as to whether projected future embedded artificial rain, salt and sulphur patterns will hold true to future conditions. Within the cultures of science, work in HEROMAT's Labs temporally compress weathering ‘events’ that happen over decades – freeze thaw cycles, salts, sulphurs – into frames of lab-managed time. Artificially subjecting stones and geomaterials to conditions they would only experience over the passage of many years, if at all, is how researchers make material weathering processes of an unknown future.

Anthropologist Laura Bear has argued that ‘our understanding of future-oriented action is still underdeveloped’ (2016: 126). If we regard artificial weathering as a case of ‘time tricking’ (Moroşanu and Ringel 2016) then it is also one of agency, an ‘attempt to modify, manage, bend, distort, speed up, slow down or structure the times they are living in’ (Moroşanu and Ringel 2016: 18). Accelerated weathering is done in labs to achieve delays to weathering in the world. Tricking time, speeding through years of winters, winds and storms, produces data necessary to assess, in the dark rooms of SEMs, whether consolidated materials may better survive into the future. While artificial weathering is a relatively mundane, even standardised practice within scientific worlds, for scholars of time, it opens up reflections on how knowledge about change over long timespans can be brought into the present. Seen from inside the testing process in Paisley, attempts to fix stone in time illuminate not only the role of scientific work in fields that work explicitly with temporal concerns, but also the contestations around slowing, interrupting or stopping weathering as material evidence of its passage.

Footnotes

Acknowledgements

This research was supported by the Arts and Humanities Research Council (AHRC) in the United Kingdom, AH/K006002/1 through the Materiality, Authenticity and Value project, hosted by John Hughes at the University of the West of Scotand, along with CI-s Siân Jones, and Tom Yarrow. The conceptualization of the project was part of these colleagues’ larger and ongoing enquiry into heritage cultures, and I thank them deeply for the opportunity to work within their networks and for introductions to their peers, and all research participants who took the time out for interviews and discussions that made this work possible. I thank John Hughes for his hospitality in Paisley and his perspicacious comments to this article in its development. The Material Life of Time conference, March 15–17 2021 provided the impetus for the paper, and I acknowledge the organizing force of Michelle Bastian as well as comments of co-panelists Emil Flatø, Anne Kveim Lie and Kristin Hussey, who suggested we develop the laboratory theme. Finally, I thank Carlijn Ruers for her gift of Ruskin's Lamp of Time which oriented this work many years before the fieldwork took place.

Declaration of conflicting interests

The author declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was supported by the Arts and Humanities Research Council (grant number AH/K006002/1), PI John Hughes, CIs Siân Jones, and Tom Yarrow.

ORCID iD

Rachel Douglas-Jones

Notes

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