Neither past nor present : Authenticity and late twentieth-century architectural heritage

It was the present moment. No one need wonder that Orlando started, pressed her hand to her heart, and turned pale. For what more terrifying revelation can there be than that it is the present moment? That we survive the shock at all is only possible because the past shelters us on one side and the future on another. But we have no time now for reflections.(Virginia Woolf, Orlando) How long does the present moment last? Where and when does the past begin and how does the present end? In physics – or more precisely in the special theory of relativity – the present can be defined as the coordinate origin in a spacetime diagram – an unextended point that separates an observer’s past and future light cones. From that point of view, the present has no duration at all; the past instantly assimilates the future without any hesitation in between. However, time perception tells us that we actually experience a ‘here and now’. Psychologists believe that the time range we perceive as the present, the socalled specious present, lasts about three seconds – the interval duration after which the brain may be said to reset its attention. This is already infinitely more than no duration at all but this recognition is still not enough to explain concepts like the present time or ‘today’ as an indicator of the contemporary. In the domain of history, the present seems to be a much more complex construction. When we speak of phenomena as contemporary, we place them in an extended present. We concede that the present encompasses the recent past and the near future – a temporal range that provides a stage for the actions and reactions that shape our world.

It was the present moment. No one need wonder that Orlando started, pressed her hand to her heart, and turned pale. For what more terrifying revelation can there be than that it is the present moment? That we survive the shock at all is only possible because the past shelters us on one side and the future on another. But we have no time now for reflections. 1

(Virginia Woolf, Orlando)
How long does the present moment last? Where and when does the past begin and how does the present end? In physics -or more precisely in the special theory of relativity -the present can be defined as the coordinate origin in a spacetime diagram -an unextended point that separates an observer's past and future light cones. From that point of view, the present has no duration at all; the past instantly assimilates the future without any hesitation in between. However, time perception tells us that we actually experience a 'here and now'. Psychologists believe that the time range we perceive as the present, the socalled specious present, lasts about three seconds -the interval duration after which the brain may be said to reset its attention.
2 This is already infinitely more than no duration at all but this recognition is still not enough to explain concepts like the present time or 'today' as an indicator of the contemporary. In the domain of history, the present seems to be a much more complex construction. When we speak of phenomena as contemporary, we place them in an extended present. We concede that the present encompasses the recent past and the near future -a temporal range that provides a stage for the actions and reactions that shape our world. It is precisely this possibility of action and intervention that differentiates the present from the past. As the past lies beyond the scope of action, we cannot alter it, though we are able to influence the way we receive and understand it as we write and rewrite its history in the present. It is this transition zone between present and past that causes trouble and which is the topic of this article. It may be difficult to define the boundaries, Neither past nor present : Authenticity and late twentiethcentury architectural heritage Tino Mager doi: 10.1017/S1359135519000125 arq (2019), 23.2, 137-148. © Cambridge University Press 2019. This is an Open Access article, distributed under the terms of the Creative Commons Attribution licence (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted re-use, distribution, and reproduction in any medium, provided the original work is properly cited. duration, and temporal distance from the now of this elusive period, but it is a crucial period, because the legacies of the just ending present are in a troubling state, suspended between currency and historicity. They are in a state of staleness. The objects of this legacy, which no longer belong to the present, do not seem to offer us any perspectives for the future. Not quite historical yet, they do not seem to connect us with a past separated from our time.
When it comes to architecture, a plethora of buildings erected in the second half of the twentieth century and especially since the 1960s currently occupy this shadowy zone between the present and past. 3 The architecture and urban planning of that decade constituted an important part of the spatial backdrop for the young baby boomer generation, influencing their living conditions and social structures, and thereby shaping them and our present, as this generation is in large part the one in charge today. At the same time, the principles of such architecture and urban planning are outdated, and the building stock is not yet a generally acknowledged part of the past -it is not yet accepted as truly historical. In addition, the buildings in question are anything but rare and they are commonly in a dilapidated condition -smoked glass has become blinded, exposed aggregate concrete has collected dirt and moss, and insensitive use and inferior maintenance have also taken a toll. So, it is not only the tricky situation in between contemporaneity and historicity that complicates our esteem for these structures, but also the degree to which they have been maintained or allowed to decay. Architecture critic Hugh Pearman aptly describes the problems accompanying this, saying: It's always the relatively recent past which is most in danger: that's when you lose some real gems, before they become more widely appreciated. It had happened to Victorian architecture, then Art Deco architecture, and it was happening to modernist architecture and its heavyweight sidekick, concrete Brutalism.
The modest valuation of the architecture of the recent past is a major problem when it comes to its protection. This is not a new phenomenon. As history shows, the appreciation of the architectural and historical interest in buildings of a certain era increases with temporal distance. Thus, the importance of antique, gothic, and baroque architecture only became acknowledged after much time had passed -sometimes centuries. The majority of the buildings of any recent epoch, on the other hand, tend to have undergone fewer changes and restorations due to their young age. This means that many buildings of the late twentieth century come with a special and nowadays highly demanded characteristic: no other stock of (historical) buildings is less altered, refurbished, and converted. 5 In other words, no other stock is so undoubtedly authentic -if indeed 'authenticity' lies in this unaltered state. It is precisely this concept -'authenticity' -that has become a pivotal concern in preservation debates. Since the 1990s, it has been the subject of fierce discussion and numerous papers have appeared on the topic. In recent publications, the author of this article has dealt in great detail with the term's genesis, the overview of these scientific papers, the discursive analysis of the term and its predecessors -and will not repeat these arguments here. 6 The focus will instead be on the concept of authenticity in relation to the architecture of the second half of the twentieth century. Curiously enough, in the 'age of authenticity', this most 'authentic' of architectural legacies is one that is just being discovered by experts in architectural preservation, but still lacks far-reaching public interest. 7 Therefore, it is crucial to enquire into the meaning of authenticity in relation to late twentieth-century architectural heritage and to examine current strategies that are applied towards their preservation and conservation. Does our use of the term 'authentic' in relation to late twentiethcentury buildings differ from how we use it in relation to other building stock? In what follows, I offer a working definition of the term and a short review of the evaluation of authenticity. I will concentrate on the situation in Europe and analyse to what extent authenticity is taken into account when dealing with (potential) monuments from this period.

'Authenticity' in a nutshell
To frame a term as complex as authenticity in a few lines, even in the specific context of architectural heritage, is a challenge. It should be said in advance that it is not possible to present the term here in all its facets, and it is even less possible to define the term precisely. 8 Much has been written about the concept and there seems to be a common vague as a historical information source, analogous to a document. Authenticity can of course also be related to design, setting, workmanship, etc. But for the value of a building as a historical source, material authenticity is of paramount importance. A fresh reconstruction may well be more vivid than a half-decayed building and at first glance give a better impression of the past. However, the reconstruction works are merely a materialisation of the knowledge of the past at the time of their execution, they are not a primary historical source with regard to the restored past itself.
Since the objects of the present are in production and the ones of the very recent past are still reproducible, why should we safeguard the material authenticity of a building stock that in large part does not yet feature historical layers and that seems to be still reproducible? The nineteenthcentury restorers believed in the reproducibility and continuation of the gothic style, for instance. Of course, centuries lay in between them and the medieval workmen, but they were convinced of their ability to completely understand and perfectly finish what they saw as imperfect medieval buildings [2]. 12 Today, the differences between fourteenth-century Gothic and nineteenth-century Neo-Gothic are more than obvious. It remains uncertain how twenty-first-century restorations of late twentieth-century buildings will be received in the future. But by keeping a focus on preserving their material authenticity, we can guarantee that future generations will still be able to deal with real twentieth-century heritage, ensuring that they will be in a position to address their own questions to these built 'documents' of the twentieth centuryquestions that may differ from those of today.

The ambiguous role of authenticity
Authenticity alone is of course not a reason for the preservation of buildings. Indeed, despite an avowed high regard for authenticity among experts and lay people alike, it seems that it is actually of secondary importance in the evaluation of historic buildings. This is a topic that is closely bound up with the precarious meanings attributed to the term. The UNESCO World Heritage Centre has played a crucial role in the emergence of the concept of authenticity regarding historic buildings. Since the formulation of the Operational Guidelines for the Implementation of the World Heritage Convention by UNESCO's World Heritage Committee in 1977, authenticity is a necessary criterium for the inclusion of cultural objects in the World Heritage List. 13 This requirement has, however, caused trouble from the very beginning.
14 One-and-a-half decades after its introduction, the Nara Conference on Authenticity (1994) was scheduled to clarify the concept. 15 However, during the conference and in its aftermath, the search for the meaning and the handling of authenticity led to a relativist view of the concept, which on the one hand is needed to cope with the worldwide diversity of material objects, but which, on the other hand, prevents a verifiable application.
understanding, but there is apparently no way to fix the concept. This fact is not an unimportant part of its ongoing topicality. 9 The meaning of authenticity in architectural heritage can best be understood by looking at the foundations of the preservation discourse in the nineteenth century. Without doubt, buildings of former centuries are appreciated for many reasons, but a primary reason for their protection lies in the impossibility of their recreation -more precisely in the recreation of their age. As John Ruskin asserted in 1849: 'the greatest glory of a building is not in its stones, nor in its gold. Its glory is in its Age' [1]. 10 A building or parts of it can be reconstructed, but 'the spirit of the dead workmen cannot be summoned up, and commanded to direct other hands, and other thoughts. And as for simple copying, it is palpably impossible.' 11 Hence, every restoration work is a product of the time of its execution -and this shows. Thus, if monuments are considered as reminders -or more precisely as sources of the past analogous to original documents -they can only be considered so if they actually derive from that time. The authenticity of a monument, a historic artefact, thus lies to a large extent in the testifying realness of its materiality. This is because its material substance guarantees the building medieval building.
In comparison with the surviving condition, numerous suggestions for changes to the façade can be seen. World Heritage, it leads to the conclusion that the outstanding authenticity of many late twentiethcentury buildings is of little importance for their estimation and protection. If authenticity is officially being asserted for twenty-first-century reconstructions of sixteenth-century buildings -as in the case of Mostar -it is a minor task to assert it for a significantly refurbished building of the late twentieth century.

20
The concept of World Heritage covers a wide range of meanings. Apart from the protection of historic objects, it serves political, economic, and cultural purposes and therefore cannot be understood as a compilation of objects of historically unimpeachable informative value. But it should not be forgotten that ICOMOS and UNESCO are major global players in shaping the discourse on the concept of authenticity. While both bodies were important in initiating discussion of the concept, this discussion has not led to definition, but rather definition is implied in the practical evaluation of the monuments in question and their subsequent inclusion into the World Heritage List. Reflecting on this, we see that it is crucial to keep in mind what purpose is to be served when talking about authenticity. The concept is a different one when it comes to the designation of a memory space or a world heritage site, or when it comes to the designation and preservation of an architectural monument that is understood to be a scientific source of information. Over time, the way in which relics of the past have been regarded has changed considerably. This is reflected in a changing conception of heritage and the words used to define this concept. The architectural legacies of the past were once called 'ancient monuments', they later became 'national memories' and, in the course of time, today's 'heritage'. Astrid Swenson A closer look into the ICOMOS evaluations of objects in the World Heritage List reveals that authenticity has hardly been a subject of adequate examination. 16 In case of doubt, authenticity is arbitrarily attributed or conceded without any statement. So, for many objects included in the World Heritage List, evaluations regarding their authenticity (a necessary prerequisite for inclusion) have never been carried out, but nonetheless authenticity has been attributed (for example, for the World Heritage Sites Cologne Cathedral, Historic Centre of Morelia, and Belfries of Belgium and France) [3]. 17 In other cases, ICOMOS evaluations have attributed 'authenticity' to recent reconstructions of buildings that no longer exist. This was done without further justification, for example, at the World Heritage Sites Old Bridge Area of the Old City of Mostar, and the Tombs of Buganda Kings at Kasubi. 18 The superficiality of the ICOMOS evaluations demonstrate that factual authenticity and its careful investigation is, in practice, often of much less importance than the assertion of authenticity. In the case of the completely destroyed Mostar bridge, the 'facsimile reconstruction' was certified to have 'a kind of truthfulness' and to give the urban landscape 'a special kind of "overall" authenticity'. 19 It is easier to simply assert authenticity than to prove it, and it is more comfortable to believe in the assertions of authentic heritage than to question the veracity of the historical narrative. If this is true for the universally acknowledged masterpieces of the tabulates some of the difficulties encountered in reconciling authenticity with repair. The lack of knowledge in preserving reinforced concrete or in handling deteriorating experimental materials plays a major role. MacDonald states: 'It is the emphasis on the honest expression of concrete that is the crux of the problem in terms of material authenticity for many postwar Modern buildings.' 27 The concrete of most postwar buildings intertwines material and aesthetic authenticity, because the surface is inseparable from the structure and the concept of the buildings. This phenomenon is not exclusive to late modernism, but it appears comparatively often here. Alongside material issues, MacDonald also outlines some cultural difficulties that complicate the discourse around preservation of late modernist buildings: 'Unrecognised nostalgia for ageing modern buildings', 'Lack of recognition/ appreciation for modern buildings', and 'Poor understanding of twentieth-century architecture (incomplete histories)'.
28 These difficulties are obviously due to the lack of historical distance and to the 'incomplete history' of the transition zone between present and past. In Europe, this transition zone issue was recognised very early in the UK. In 1987, ten years prior to MacDonald's article, the Department of the Environment Circular 8/87 had already defined the time limit between past and present and introduced the Thirty-Year Rule that grants eligibility for the listing of buildings that were begun at least thirty years ago. Moreover, a Ten-Year Rule was introduced at the same time that -under certain, action-requiring conditions -considers at least ten-year-old buildings for listing. 29 This provident law makes allowance for the problem of a lack of historical distance and underlines a valuation for the most recent past. It facilitates the implementation of forwardlooking decisions considering listing, but it does not simplify the preceding philosophical issues of recognition and appraisal. Today, the timespan of thirty years is a guideline for listing in many European countries, though some stipulate a minimum age of fifty years. 30 Twenty years after Susan MacDonald's article, the research group 'Which Monuments, Which Modernity?' produced a position paper that draws a slightly different conclusion when it comes to material aspects. 31 While the material and structural specificities of postwar buildings are acknowledged, they are seen as characteristic of the period and, in this, as no different from the buildings of any other period. Of course, the architecture of the late twentieth century developed its own unique features, but therein it corresponds to the architectures of all other periods. A brutalist concrete structure is no more unusual for global architectural history than a timbered house or a fieldstone building. But it is comparatively new and therefore there is generally less experience in maintaining and preserving it. 'Which Monuments, Which Modernity?' points out that the main highlights these conceptual shifts and describes the changing ideas of what was considered valuable in remains from the past. She also shows how the linguistic changes not only went along with such development, but in turn also influenced it. 21 The same phenomenon is seen in other languages, as Swenson demonstrates for French and German. 22 To put it bluntly, the monument -'something that reminds' as the word monument literally means -is no longer a material reminder, but has turned into something we actively select as inheritance. 23 Pierre Nora's introduction of the concept of memory space sharpened awareness of the more or less arbitrary attribution of historical meaning to things. 24 Thus, it is not the object that reminds us, but rather it is we who attribute current memories to historical things. This provides an enormous scope for designating meanings to things and classing things as monuments. That scope is larger for younger objects because they are still in the process of being appraised, and thus, of becoming historical. The word heritage reflects this freedom -it does not refer to material expressions of determined memories; rather, it refers to the willingness to accept and define an inheritance. This is precisely how heritage is defined in present position papers.  25 This valuable expression of the social and cultural openness of the notion of 'heritage' is undoubtedly pioneering, but it also entails shifts in the understanding of the authenticity of these resources from the past and therefore in the ways of preserving and transferring them. If historical objects are understood less as monuments that allow documentary insights into the past, rather than as freely associable places of remembrance, then their material authenticity -guarantor for their documentary value -becomes secondary. At the same time, the assertion of authenticity seems to become increasingly important, regardless of its presence, as can be seen in the context of the World Heritage.

Reflecting the heritage of the recent past
Although authenticity is a popular theme, consideration of its application to the heritage of the recent past is rare. Susan MacDonald's 1997 article 'Authenticity is More than Skin Deep' is one of the earliest attempts to grasp the concept of authenticity in relation to postwar architecture. 26 MacDonald pays special attention to concrete buildings in Britain and aims to clarify the specificities of such building stock. She explains several material, design, and production issues typical for these buildings, and In practice, however, no particular emphasis is placed on the authenticity of the building stock in question when these crucial decisions are made.

The material authenticity of listed buildings
Today, while the architectural legacy of the late twentieth century is coming into focus as the potential object of preservation, many controversies are emerging, especially when it comes to the appreciation and consequent listing of unusual buildings such as the conference centre ICC problems concerning preservation are not only legal or technical; rather, they lie in the selection of buildings to be preserved; the consequent imparting of status to the buildings; and the concepts used in dealing with them. These issues were recognised in the 1990s. A careful evaluation of the building's authenticity may be helpful in the selection of potential heritage from a vast stock of buildings, for it is important to underline the information value of this young heritage and when decisions on necessary adaptions are pending. and Hans Schoszberger. 33 The commercial building is part of an architectural ensemble facing the Kaiser Wilhelm Memorial Church. The name, Bikini House, was coined soon after construction because it housed a production facility for women's garments and featured an 'air storey', separating the upper from the lower floors. Like the two parts of a bikini, the lower and upper floors of the building seemed to be disconnected but belonged together. In 1978, the gap was converted into a normal storey, but the name remained. Bikini House is registered in Berlin's heritage list, where it is recorded as a building from the 1950s. It does look like a building from the 1950s, especially from the front. Indeed, it looks even more 1950s than it used to look in the 1950s -at least that is the impression one gets when comparing it to old photographs. The reason is because the building is in fact brand new. Between 2010 and 2013, it was converted into a shopping mall, and this renovation entailed the loss of its façade, the brass-framed windows, its friezes, its characteristic stair towers, etc. In short, everything but the supporting structure was demolished. The result appears visually coherent in comparison with the new buildings within close proximity [6]. However, such treatment seems to be intolerable for a listed monument. Surprisingly, it is not, and Bikini House is still listed as a 1950s building. Curiously, the percentage of original material of most surviving temples or Romanesque churches is certainly higher; their rare material remains are painstakingly treasured. Bikini House is but one example of a twentieth-century monument whose material authenticity has been treated without due regard. Berlin (1975-9, Ralf Schüler and Ursulina Schüler-Witte) [4]. This spectacular building is one of the largest conference centres in the world -a mostly windowless and aluminium-clad structural expressionist ensemble that resembles a spaceship rather than a building. The enormous operating costs and the inflexible interior of the awardwinning venue make it increasingly unattractive and a challenge to adapt its use. So, will it be preserved? Other structures, widely acknowledged as architectural masterpieces, have not been so lucky. Take, for example, the residential estate Robin Hood Gardens (1969-72, Alison and Peter Smithson) in London, which is currently being torn down; or the already demolished University of Toulouse, Le Mirail (1961-71, Georges Candilis, Alexis Josic, and Shadrach Woods) [5]. Despite their architectural qualities and their high degree of authenticity these recent much-lamented cases show that architectural quality combined with material authenticity have often not been enough to ensure preservation. But we need not despair, for attitudes can change as time goes on. We have seen this in a positive change in attitude towards the value of industrial heritage. While the term industrial culture was only recognised by the Council of Europe in 1984, there are now a large number of registered sites of industrial heritage and, since the 1990s, many industrial sites have also been included in the World Heritage List. 32 As the buildings are contemplated from a larger temporal distance, they may eventually attract widespread appreciation. But nonetheless, numerous examples show that listed postwar buildings receive 'rougher' treatment than older monuments and that their material authenticity hardly seems to be regarded as important. We will take the example of Bikini House, a landmark building in the heart of Berlin's Zoo area, built between 1955 and 1957 by Paul Schwebes Tino Mager Neither past nor present measures comparable to the examples mentioned above will unquestionably have influence on the notion of 'historical monument' because the outcomes are designated as such. 36 Our understanding of architectural heritage is not only defined by laws and theory, but also by acts of designation. 37 In the long term, such accumulated radical interventions may affect the idea of restoration at large, because these actions are carried out officially and are committed against the listed monuments and their material authenticity.
Another example is Park Hill in Sheffield. The Grade II* listed building complex is currently being gutted and redesigned. Everything but its shell will be replaced by the developers -a slightly awkward coalition between English Heritage and the property developer Urban Splash. 34 Yet the altered building complex is and will remain the Grade II* monument that it used to be -at least on paper. 35 In reality, it has essentially lost its material authenticity [7,8]. While there are also numerous examples of exemplary renovations of late twentieth-century buildings, the countless 7 Park Hill before reconstruction. The building is in a bad condition, but some remarkable details are still visible, such as the balcony balustrades made of filigree concrete.
8 Park Hill after reconstruction. The building, which has been gutted in the meantime, appears fresh and contemporary. Details such as the concrete balcony balustrades are lost. shipbuilding research centre. The interior contains a flow channel with 3,300 tons of water that can be circulated at ten metres per second to carry out experiments on ship models. 40 Many of the blue façade panels were in a scruffy condition and irreversibly corroded. In regard to the renovation, the question arose as to what extent the building should be allowed to age visually, and to what extent the authenticity of this pop architecture is linked to the radiance of its colourful surfaces. The appreciation of the tank's shabby look as dignified ageing seemed as difficult as the idea of replacing Leo's original façade with a new one. Whereas signs of ageing may be harmonised with the historic look of buildings from former centuries, they appear quite unfavourable in terms of the aesthetic indulgence of a four-decades-old technical building in gaudy colours.
In the case of UT 2, it fortunately turned out that the façade panels are still in production -identical in construction with the ones from the time of the tank's erection. 41 Consequently, all damaged panels were replaced and the tank retained its original look since, technically, the new façade is identical to the original one. The building thereby revealed its status in between past and present. UT 2 is a technical monument of the 1970s, but some of its components link it to current production methods. For this reason, it could be argued that the material exchange of the panels has a limited effect on the authenticity of the building. This is because the new and old panels are structurally identical and no outmoded craftsmanship was needed to install them, and hence no meaningful traces of time -or more precisely, no traces of history -were blurred [10]. Nevertheless, questions arise about the originality and historicity of the material substance. The building appears in mint condition because it was deprived of its age in certain parts. The flawless appearance therefore Authenticity of material and design As MacDonald asserted, concerning the buildings of the recent past, the relation between authenticity of material and authenticity of design is a complicated one. The materials -concrete, exposed aggregate concrete, synthetic materials, metals, etc. -offer surfaces that age differently to the surfaces of stone, brick, or wood. This is a challenge that is highly topical today and, as in the conservation of art of the late twentieth century, has by no means been mastered yet despite much attention. 38 However, this does not have to be an obstacle to the appropriate restoration of such buildings. If those responsible take the trouble to realise the value of the building and to discuss its peculiar position in history, its material authenticity can be largely preserved. To take an example, the decision of how to deal with a rusted sandwich panel façade made of sheet metal and polyurethane foam is somewhat complex but not unsolvable. This problem arose when Ludwig Leo's listed circulating tank UT 2 (Umlauftank UT 2) from 1974 became an object for renovation in 2014 [9]. 39 The unique pink and blue building houses the Technical University of Berlin's 9 Umlauftank 2 before restoration.
10 Umlauftank 2 after restoration. On the other hand, authenticity is arbitrarily attributed to buildings, as in the above-mentioned World Heritage Sites Old Bridge Area of the Old City of Mostar or the Tombs of Buganda Kings at Kasubi.
The practice of regarding 'authenticity' as a freely available attribute, not strictly attached to the material authenticity of the building in question, and the practice of failing to carry out any strict evaluation of authenticity according to this criterion before listing, threatens the recognition of the importance of material authenticity as a repository of historical fact. Ignoring the potential importance of material authenticity also means that, while many late modernist buildings are authentic in this sense, the attribute is hardly beneficial to their prospects for appreciation and preservation. Unfortunately, the authenticity of late twentieth-century buildings sometimes even seems to be regarded as comparatively insignificant. This is a pity, because the high degree of authenticity that can justifiably be attributed to a large number of these buildings is unusual -we do not find it in any other building stock. It is particularly regrettable since it is difficult to promote the momentarily outdated aesthetics of these late twentiethcentury buildings. In light of the apparently infinite number of these buildings, it is equally difficult to promote recognition that we have both an urgent need and an opportunity to select and preserve the best. Monument preservation requires a consolidation of its core principles and those concerned with the preservation of our heritage urgently need to promote a deeper public understanding. The aim of historic preservation should not be the beautification of human habitat but the safeguarding of inimitable, truly authentic layers of the historical artefact. But even in this age of authenticity, the authenticity of buildings is hardly a guarantor that their value will be acknowledged. Thus, Hugh Pearman is proved right -the relatively recent past is once again the one most in danger.
To conclude, I return to the opening of this article and the curious flexibility of the conceptual present. Given the versatile ways in which we claim age-old relics for current purposes, the expansion of the present appears to be limitless. But with a view to the time-bound nature of human achievements, it should be noted that even the recent past, along with its architecture, is slowly but surely escaping from our present grasp as it becomes irreproducible and consequently historical. Therefore, the material authenticity of late twentieth-century buildings must not be regarded superficially, nor valued differently from the authenticity of buildings from other eras. By the time Orlando noticed that 'it was the present moment', that moment had already gone. Likewise, before we are aware of it, the recent past is becoming a truly historical one, which is why we should handle its legacy with appropriate respect. goes hand-in-hand with the absence of any patina and follows an understanding of monuments that is oriented towards aesthetic rather than historical aspects. Although an exchange of the corroded façade elements was indispensable in this case, it must be questioned how authenticity is to be understood in relation to buildings of the second half of the twentieth century. If, instead of monument preservation, the visualisation of the situation during the construction period is given priority, an authenticity concept that refers to historical reliability is obsolete. However, historic preservation also considers the duration of the existence of buildings. The concept of historical authenticity must therefore take this period into account, even for buildings from the recent past. If authenticity is arbitrarily accredited or if the understanding of authenticity is limited primarily to an original state, historic preservation becomes questionable when it comes to claiming authority in the safeguarding of historical sources.
At this point it is worth mentioning that Alois Riegl's renowned age value (Alterswert) is commonly mistaken as a value of age in John Ruskin's sense. 42 But unlike Ruskin, Riegl does not refer to age as a non-(re)producible component of historical buildings. He rather talks about a quasi-religious experience of genesis and demise that becomes evident through the contemplation of traces of transience. 43 In this respect, rust and neglect actually appear to be clearer marks of this process than the rather romantic signs of the ageing of ancient monuments. But due to the small time lag separating the present from the time of the erection of late modern buildings, the impression of lacking maintenance represses any kind of religious experience. Here the question arises of which parameters favour the acceptance of the patina of architecture of the late twentieth century. How is it possible to evaluate traces of time, which today are perceived as deficiencies, as testimony to a time span that connects the present with a young past that is no longer contemporary? Perhaps the increasing temporal distance to the buildings in question and the historical appreciation it entails will contribute to a new perspective on phenomena that currently appear to be more of a deficiency.

Vexed, and poorly defined
In this article, I have argued that 'authenticity' -that vexed and often poorly defined attribute of architectural heritage -could usefully put more emphasis on the material authenticity of the building, since the authentic original or historical material of a structure provides a potential scientific source. Despite the repeated emphasis on the importance of the concept of authenticity in debates and policies concerning architectural heritage conservation, we find that, on the one hand, highly materially authentic listed late twentieth-century monuments are subject to fundamental material and structural changes.