Part 4 of the Sheet Metal Series
Walk down any street of late 19th or early 20th century housing in Belgium, France, or the Netherlands, and look up. The grey-blue metal at the roofline — the gutters, the dormer window surrounds, the decorative crests and finials, the capped cornices — is almost always zinc.
Zinc is the dominant sheet metal of the urban architecture of this period in these countries, and its presence is so ubiquitous that it has become invisible. People walk past zinc dormers, zinc gutters, and zinc ornamental details every day without registering what they are looking at. They notice the stone, the brick, the ironwork. The zinc, somehow, disappears into the background.
This invisibility is partly zinc’s character — its grey-blue colour is subtle, its surface texture is quiet. And it is partly a consequence of how zinc ages: not dramatically, like copper, but gradually and unremarkably, until the moment it fails — which, if maintenance has been deferred long enough, can be sudden and consequential.
Understanding zinc — where it came from, how it works, and how to restore it correctly — is essential for anyone working on historic buildings in Belgium, France, or the Netherlands.
The Belgian origin story
Zinc as an architectural material has a specifically Belgian origin, and that origin shapes everything about how it came to define the urban architecture of northern Europe.
In 1806, the chemist Jean-Jacques Daniel Dony was granted the sole mining rights to the calamine deposits of Vieille Montagne — the “Old Mountain” between Liège and Aachen, on what is now the Belgian-German border. Dony developed the first industrial process for smelting zinc, and the company he founded — the Société Anonyme des Mines et Fonderies de Zinc de la Vieille Montagne, established in its definitive form in 1837 — became the dominant zinc producer in Europe for the next century.
From their works at Angleur near Liège, Vieille Montagne produced zinc sheet, zinc ornaments, and zinc architectural elements that were sold across Europe and beyond. Their catalogue — the Album V.M., first published in the 1870s and running to multiple editions — offered a complete range of architectural zinc: gutters, downpipes, dormer window surrounds, decorative crests, finials, ornamental panels, and the distinctive oval and circular window frames that became a defining feature of the Belgian urban roof.
In the 20th century, Vieille Montagne evolved through a series of mergers and acquisitions into VMZinc, which continues today as the leading manufacturer of architectural zinc in Europe — and which still produces ornamental zinc elements in direct continuity with the catalogue tradition of the 19th century. Vieille Montagne also eventually became part of Umicore, the global materials technology company headquartered in Brussels.
The zinc that built the Belgian streetscape came, in large part, from one company and one region. That is a remarkable fact.
The catalogue tradition — ordering your roof by post
The Vieille Montagne catalogue was the architectural zinc equivalent of the Mesker Bros. cast iron catalogue discussed in the gietijzer post in this series. An architect or a building owner could select standard dormer window surrounds, decorative crests, gutters, and ornamental details from illustrated pages, order them by number, and have them delivered by rail.
This catalogue logic explains something that anyone who looks carefully at Belgian urban housing notices: the similarity of zinc details across buildings by different architects in different streets and different cities. The same dormer window surround profile appears on a house in Antwerp and on a house in Brussels and on a house in Ghent. The same ornamental crest appears on multiple buildings in a single street. They came from the same catalogue. They were ordered from the same company.
The œil-de-bœuf — the oval or circular zinc-framed window that appears in the attic storey of countless Belgian houses — is perhaps the most characteristic example. These frames were standard catalogue items, produced in a range of sizes, and installed by the thousands across the country between roughly 1870 and 1930.
They are now disappearing.
Not because the buildings are being demolished — many are protected. But because when a zinc œil-de-bœuf or a zinc dormer surround fails, it is often replaced with a modern aluminium or plastic equivalent rather than being restored or reproduced inzinc. And because when buildings are demolished, the zinc elements are removed and sold — increasingly, they appear in antique markets and on platforms like 1stdibs, repurposed as decorative mirrors or architectural curiosities, far from the rooflines where they belong.
They are not yet rare. Walking through the older neighbourhoods of any Belgian city, you will still see them in place — some in good condition, some failing, some already replaced. But the trajectory is clear. Each one that leaves its original position is one fewer that can be studied, reproduced, or restored in place.
How zinc works — and why it fails
Zinc sheet used in architecture is not pure zinc. Architectural zinc is an alloy — typically zinc with small additions of copper and titanium — that has significantly better mechanical properties than pure zinc: higher strength, better resistance to creep under load, and a more controlled patination behaviour.
Fresh architectural zinc has a bright, slightly reflective surface. Over months and years, it develops a patina of zinc carbonate and zinc hydroxide — the characteristic grey-blue colour. This patina is stable and protective, and a patinated zinc surface has good longterm weather resistance.
Zinc fails through several mechanisms:
Perforation corrosion — pinholes that develop over time, particularly in areas where water ponds rather than draining freely. Zinc gutters that have inadequate falls, or that have been blocked by debris, develop perforation corrosion in the lowest areas.
Thermal fatigue — zinc expands and contracts significantly with temperature, and installations that do not allow adequate movement will crack at stress concentration points. This is why correct bay sizing and expansion joint provision are as important in zinc work as in lead.
Contact corrosion — zinc in contact with copper, or exposed to runoff from copper above it, corrodes rapidly. The electrochemical incompatibility of zinc and copper is the most common source of unexpected zinc failure in historic buildings where different metals have been used at different periods.
The roofing felt patch — discussed in the gutters post earlier in this series. A torchapplied roofing felt patch over a failing zinc gutter is not a repair. It traps moisture, accelerates corrosion beneath it, and converts a limited failure into a comprehensive one. This cannot be said often enough or clearly enough.
The dormer window surrounds — a craft worth preserving
The zinc dormer window surrounds of the late 19th and early 20th century are more than functional objects. They are designed artefacts — the profiles, the mouldings, the decorative details were drawn by architects and draughtsmen, refined through multiple catalogue editions, and installed by craftspeople who understood both the material and the tradition.
Walking through Boom in Antwerp province, you can still see intact examples standing in their original positions — waiting, essentially, for someone to recognise what they are and restore them rather than replace them.
The question of whether these surrounds can be reproduced — when an original has failed beyond repair — is the same question as for the gietijzer rondelles. If an intact original can be found, or if sufficient documentation exists of the original profile, reproduction is possible. VMZinc continues to produce standard ornamental zinc elements. For non-standard profiles, specialist fabricators can work from drawings or surviving examples.
The knowledge of how to work with zinc — to cut, form, solder, and install it correctly — is the limiting factor. Zinc work is a specific skill, distinct from general roofing. The zinkwerker who understands the material and the tradition is a craftsperson worth knowing.
Resources for the curious
For anyone who wants to go deeper into the history of architectural zinc in Belgium and France, several resources deserve mention.
The Science Museum Group in London holds original Vieille Montagne catalogues and technical pamphlets in its collection — including the Album V.M. of 1880, with 75 pages of numbered zinc ornaments and architectural elements, and the roofing instruction pamphlets that taught a generation of zinkwerkers how to use the material.
The Museum of Technology (MOT) in Brussels holds Vieille Montagne company records and technical documentation.
The University of Liège digital archive (DONum) has digitised some Vieille Montagne exhibition catalogues.
The parallel French tradition is documented in the Bonfils & Fesquet catalogue —Ornements en zinc, cuivre, tôle plomb — and the American equivalent in the WH Mullins Architectural Ornaments Catalogue and Sargent & Co hardware catalogues.
If anyone in the Guild has access to a physical copy of an original Vieille Montagne ornament catalogue — or knows of one in a local archive — that would be a significant resource for the restoration community.
A question to the Guild
The zinc dormer surround question — how to approach the restoration of a failing original, and where to source reproduction elements when the original cannot be saved — seems like exactly the territory where Guild knowledge matters.
Has anyone worked on the restoration of zinc ornamental elements from the late 19th century catalogue tradition? And has anyone found reliable sources for reproduction zinc elements — either through VMZinc or through specialist fabricators — that match the profiles of original historic work?
The grey-blue zinc on Belgian rooflines is not background detail. It is part of the language of the architecture. It deserves the same attention as the stone and the ironwork below it.
RestoreFacade Guild — for the craftspeople who look up.
Next in the series: Tin — the forgotten sheet metal, and why its near-disappearance matters.