When William Morris declared, “The subject of material is clearly the foundation of architecture,” he might be thought to have been saying something relatively straightforward and uncontroversial.1 Yet commonsensical though his statement might seem, it contains plenty of room for uncertainty. Are we sure that we know what “material” is? And can we agree as to what exactly it is that architecture is expected to do with materials? Architecture, as Antoine Picon writes, operates in a state of constant tension between the resistance of matter to human endeavors and the desire to animate matter, to make it communicate. Attempts to overcome the opacity of matter have a long history, one that is not over yet; and for architects, since architecture has been a significant actor in that history, the pressure on them to make matter expressive has weighed heavily. While architects have been only too aware of their obligations in relation to matter, historians and theorists have had limited success in bringing matter into the discourse of architecture. The books by Antoine Picon and Ákos Moravánszky reviewed here offer some suggestions as to how we, as historians, might do better, especially in relation to the advent of digital culture, although the problem itself is far from recent.Early in The Materiality of Architecture, Picon says that there are two kinds of architecture books: those that aspire to contribute to the discipline and those that use architectural questions as a springboard for other inquiries. His book belongs, initially, to the latter category, though in its later sections, which show signs of having been rather hastily put together, it is more addressed to practice, re-rehearsing in part some of the discussion in his previous Ornament: The Politics of Architecture and Subjectivity (2013).2 Picon distinguishes between “matter,” “materials,” and “materiality,” and his definition of “materiality,” given the confusion that surrounds the use of that term, is worth noting. “Materiality” is not matter, but “designates the way humans relate to matter and materials through the prism of their beliefs, knowledge, and practices, architecture being one of these practices” (19). This emphasis on the relational nature of materiality is helpful and promises much. It makes materiality into a historical concept, contingent on circumstances and modes of thought. It allows Picon to propose that there are “regimes of materiality,” and that we, as historians, might see materiality as a shifting scene. For architects, rather than treating material as a timeless constant, it places the onus on them to represent this relationship in architecture and to be alert to changes in it. The whole book could have been devoted to exploring these “regimes of materiality” through history, but as it stands, they are only sketched out in a rather abbreviated way.Insofar as the book is addressed to nonarchitects, Picon’s main concern is to show how architecture might reflect on the “material turn” in the humanities—a tendency toward which he, mistrustful of the desire to attribute agency to nonhuman things, is by no means sympathetic. As a move largely developed to counteract the logocentrism of Western thought, the material turn has privileged sensation over communication. Yet architecture, as Picon argues, presents in a way few other practices do the actuality of the relationship between matter and humans, the desire for matter to be made to communicate, however paradoxical it may be to try to make mute matter speak.Up to a point, the book may register with an audience outside architecture—and indeed some of the content will seem very familiar and not particularly novel to an architectural audience. But there are parts of the book that are dense with architectural material of a kind that nonarchitectural readers may well struggle with. This is particularly so when Picon writes about digital culture’s impact on the materiality of architecture. What might well be the core of the book—the undoubted but inconclusive effects of the digital on materiality, and the ways that this relationship manifests itself in architecture—turns out to be a disappointment. Unlike the measured argument and precision of the earlier chapters, a stream of consciousness takes over, with a tendency to make general statements on the basis of highly individual instances. Maybe this is the best that can be expected in the present state of uncertainty around the digital, but others, notably Mario Carpo, have achieved rather more succinct and closely argued analyses of the transitions taking place without being seduced by the rhetoric of the digital avant-garde.3 Picon seems a little too susceptible to some of its exponents’ claims, although he is, ultimately, skeptical of how far the digital has changed expectations for architecture.The digital is in some ways the perfect test for the argument that materiality lies in the relationship between the physical aspects of phenomena and the human responses to them. Picon is doubtful of the claims of the digital avant-garde to have discovered a “new materialism,” yet the merit of his definition of materiality is that it makes it possible to shift attention from the substance, which is just as necessary to architecture as it always was, to the other half of the equation, the human component of the relationship. It is in how the digital has changed human perception, creating “a networked personality that resides simultaneously within and outside the body,” that the strength of his argument might lie (115).Picon is not much interested in materials themselves, which is a pity, for there is recent scholarship that does indeed do some of the things that he would like to see introduced into the history and theory of architecture. I share Picon’s reservations about the current academic emphasis on the performative agency of materials and also his resistance to the phenomenologists’ tendency to treat materials as timeless and universal, but there has nonetheless been some recent writing about materials that recognizes and explores—in the way Picon would like to see happening—the capacity of materials to “stage” encounters between people, whether in political or spiritual terms.To explore the historicity of material, though by different means, is also the purpose of Ákos Moravánszky’s Metamorphism. Neither a construction handbook nor a work of architectural history nor a treatise on the iconology of materials, it looks at the way the practice of design has advanced the discourse about material. Moravánszky is interested in materials and their use by architects, which gives his book an actuality that Picon’s lacks. Although written primarily for the discipline of architecture, Metamorphism also reaches further, aiming, by looking at architecture, to bridge the gap between material research, with its philosophically unconsidered results, and a theoretical debate about the “new materialism,” where those results are generally ignored. Metamorphism shows not only how architects have fulfilled existing notions of what materials are but how they have, in addition, sometimes modified such notions or extended them beyond the reasoning of philosophers. Moravánszky quotes Adorno’s comment about materials: “History has accumulated in them, and spirit permeates them” (16). What Adorno might have meant and the part architects have played in the process of forming how we perceive materials are underlying themes of the book.The core of Metamorphism is the nineteenth-century German architect Gottfried Semper’s theory of Stoffwechsel, the transfer of forms originally connected with the way one material was processed into other materials. As a transformative process, Stoffwechsel aligns with and partly illuminates the long-standing view of architecture as, in the words of Alvar Aalto, “the turning of a worthless stone into a nugget of gold” (9). There are more than twice as many references to Semper as there are to any other figure in Moravánszky’s index, and as an exposition of Semper, by no means always the easiest of writers to follow, Moravánszky’s betters any other that I know. A little more attention to Semper might have saved Picon much trouble in his efforts to find a way to discuss the expressivity of materials that was not reliant on analogies with language. Semper had already solved this problem with his theory of “practical aesthetics,” which allowed for a remarkably flexible way of thinking about material, drawing, like Karl Marx, with whom he had some ideas in common about metamorphism, from nineteenth-century biology. Briefly, Semper’s scheme conceived material in relation to four properties—pliability and resistance to tearing; malleability, or capability of being hardened; resistance to compression; and reactive strength, or suitability for being worked by removal of parts—and four processes—textiles, ceramics, carpentry or tectonics, and stereotomy or shaping. The movement of actual materials across these properties and processes, and their recombination in different arrangements, is what gives rise to the expressiveness of any particular material. Stoffwechsel is a dynamic theory that allows for an oscillation of matter between nature and technology, science and sensuality. In the five central chapters of his book, Moravánszky explores the implications of this, and it is his purpose to show the continuing relevance of Stoffwechsel to how we might think about materials today. At the same time, he offers a corrective to some of the representations of Semper’s thought in recent years, such as the way it has been interpreted as privileging surface, or the misappropriation of Semper’s very particular use of “tectonic” to mean structure in general.What makes Metamorphism especially engaging to read is that the exploration of ideas takes place largely through the buildings that Moravánszky discusses. These are not simply examples or illustrations; rather, it is through them that he carries the argument forward, a rare demonstration of what it means to think through buildings. Moravánszky’s extensive knowledge of Central European architecture and architectural culture gives him a different perspective from that of most recent writing on architectural theory. His stock of buildings is not altogether familiar; it contains some surprises, and one often feels that he has far more to say about them than he has allowed himself, for the sake of constraining the book’s size and coherence. Based on a lifetime of thinking about the material aspects of architecture, this book is full of insights into architecture and its potentiality as a cultural medium.When it comes to the discussion of very recent architecture, Moravánszky is critical of talk of “immateriality” and “atmospheres,” for, as he emphasizes, these effects rely just as much on materials as do seemingly more substantial works. Nor is this celebration of the supposedly ephemeral especially new. Semper saw the origins of architecture as arising out of the “haze of carnival candles,” but he did not take this to mean a virtualization of reality, any more than he thought that polychromy, about which he also wrote, implied the dissolution of material. Transformation runs through the entire history of architecture, and while the forms that these transformations take may change as a result of digital practices, the process of transformation remains broadly the same. Like Picon, Moravánszky regrets the failure of modern scientific culture to find the terms with which to talk about materials beyond their physical properties and performance, and to recognize their cultural resonances, their symbolic richness. Stoffwechsel may not lead us to new design strategies, but it does offer a way to see materials, as manifested in architecture, as products of a continuing historical interface between technology and culture.Metamorphism is a superbly produced book. Although originally written in German, its English version reads not at all like a translation but as a new text, and it is illustrated by the author’s own excellent photographs, all of them beautifully printed. It is a pleasure both to read and to handle.