How Weathering Masks the True Shell Content of Portland Stone
Historic Portland Stone buildings across London may appear cleaner and more refined today than they once were, a phenomenon now being attributed to the natural weathering process that dulls the shells over time.
Historically, there was no range selection when extracting Portland Stone. Stone was quarried from various sites on the island and shipped from Portland port via the English Channel up the River Thames to the heart of London. Once in the capital, the stone was worked on-site, with only the cleaner stones being set aside for intricate carving work due to their ease of use. In essence, if a stone remained intact throughout extraction, transport, and onsite manufacture, it was utilised for the project regardless of its shell content.
Over the years, natural weathering has altered the appearance of these stones. As the free calcite in the stone migrates to the surface, it naturally seals the stone and softens the visual impact of the shells. This process gives the impression that fewer shells were present in the original stone, even though many buildings were constructed using stone with significant shell content. Notable examples of this can be seen at the British Museum, Salisbury Court, St Paul’s Cathedral, and Unilever House.
British Museum
St Paul's Cathedral
Sailsbury Court
Unilever House
Unilever House, in particular, demonstrates this weathering effect vividly as it has been recently cleaned. Although the building’s overall appearance might lead some to believe that only the cleaner Basebed was used, a closer inspection of individual stones reveals the shells that were once prominent. Similarly, St Paul’s Cathedral, originally built with Heritage Portland Stone blocks, shows that the high shell content of the base stone was simply masked by centuries of natural processes. For years, Basebed was supplied for repair works, yet a detailed examination of the cathedral highlights how shelly the stone would have been when Sir Christopher Wren first set construction in 1675.
The common perception that historic buildings were constructed exclusively from the cleaner stones is now being challenged. Embracing the natural beauty of geology not only reduces the carbon footprint and cost of modern projects but also preserve the timeless charm and character of London’s architecture.
Explore London with Albion Stone
Albion Stone is pleased to offer a bespoke tour of London, tailored specifically to your needs and hosted by our Business Development Manager, Ben Levy. On this tour, you will have the opportunity to view firsthand examples of the natural weathering process on buildings near your project location. We can also highlight more recent buildings that utilise your specified stone type, providing valuable insights into the evolving application of Portland Stone in contemporary architecture.
To arrange a customised tour of London or to organise our mine/factory visit, please contact us today. Let us help you uncover the hidden legacy of Portland Stone and discover the unique characteristics that define your project’s architectural heritage.
Albion Stone, a fourth generation family business pride ourselves on having a helpful and skilled workforce as well as modern and traditional manufacturing process to enable us to produce the highest quality Portland Stone with minimal environmental impact.
