Last year I was asked to restore a pair of carved sandstone urns on a heritage property in the Hunter Valley. The urns were original to the 1870s homestead—beautifully proportioned, with acanthus leaf decoration and gadrooned bases. But a century and a half of Australian weather had taken its toll. One urn had lost significant surface detail on its exposed western face. The other had a large section missing entirely, broken off during a storm decades ago.

Twenty years ago, I would have approached this restoration the way stonemasons have always done it: study the surviving detail, take measurements, make drawings, and carve the replacement sections by hand, using the intact portions as reference. It’s skilled work and it produces good results, but it relies heavily on the mason’s interpretation of what the original looked like.

Today I have a different tool available. I scan the stone digitally before I pick up a chisel.

What 3D Scanning Does for Restoration

There are two primary scanning technologies I use for stone restoration work.

Photogrammetry

Photogrammetry builds a 3D model from overlapping photographs. You photograph the stone from multiple angles—typically 50-200 photos for a single element—and software reconstructs the three-dimensional form by analysing the visual overlap between images.

The quality of the result depends on the quality and quantity of photographs, the lighting conditions, and the surface characteristics of the stone. Carved stone with good surface texture photographs well. Highly polished or very wet stone is more difficult.

I use Agisoft Metashape for most of my photogrammetry work. The software runs on a standard desktop computer (though processing is faster with a good graphics card) and produces detailed 3D meshes that I can examine, measure, and manipulate digitally.

For the Hunter Valley urns, I captured approximately 150 photographs of each urn, including close-up detail shots of the acanthus leaf carving. The resulting 3D models were accurate to within 1-2mm—more than sufficient for restoration planning.

Laser Scanning

Laser scanners (LiDAR) project a beam of light across the surface and measure the time it takes to return, building a point cloud—millions of individual measured points that together describe the surface geometry.

Laser scanning is faster than photogrammetry for large objects and produces highly accurate measurements (sub-millimetre in many cases). It’s less dependent on lighting conditions and surface texture. The equipment is more expensive—a good handheld laser scanner costs $15,000-$50,000—but the investment pays for itself on larger projects.

For architectural restoration work where multiple elements need scanning (an entire facade of carved capitals, for example), laser scanning is significantly more efficient than photogrammetry.

How I Used Scanning on the Hunter Valley Project

The digital scans gave me three things that traditional methods couldn’t provide.

A permanent record. Before any restoration work began, I had a precise digital record of the urns in their current state. This documentation is valuable for the property’s heritage records and provides a baseline for future conservation assessments.

Mirror-image reconstruction. Because the two urns were originally identical (as a matched pair), I could digitally mirror the intact sections of one urn to reconstruct the missing sections of the other. The broken urn was missing a large portion of its bowl section. By mirroring the corresponding section from the intact urn, I could create a precise template for the replacement carving.

CNC roughing templates. I exported the digital model of the replacement sections to our CNC router, which roughed out the basic forms from new sandstone blocks. I then hand-finished the surfaces to match the texture and character of the original hand-carved stone.

The combination of digital scanning, CNC roughing, and hand finishing produced a restoration that’s dimensionally precise and texturally authentic. The replacement sections match the originals in form and surface quality in a way that would have been very difficult to achieve by measurement and hand carving alone.

Applications Beyond Individual Restorations

Stone scanning has broader applications that I’m increasingly incorporating into my practice.

Heritage Documentation

Australian heritage buildings with significant stone carving should be scanned while they’re still in good condition. When restoration is eventually needed—and with sandstone in Australian conditions, it’s a matter of when, not if—having a detailed digital record of the original surface dramatically improves the quality and accuracy of the work.

The Heritage Council of NSW and equivalent bodies in other states are beginning to require or recommend digital documentation of heritage stone elements. This trend will accelerate as the technology becomes cheaper and more accessible.

Pattern Libraries

Over the past two years, I’ve been building a digital library of carved stone elements from projects I work on—capitals, cornices, keystones, moulding profiles, ornamental details. When a new project requires a classical element, I can reference the library for accurate proportions and detail rather than relying on printed reference books.

This library is also useful for client communication. I can show a client a 3D model of a carved element, rotate it, zoom into details, and discuss modifications before any stone is cut. This saves time and reduces the risk of misunderstandings about the finished product.

Condition Monitoring

By scanning a stone element at intervals—annually for exposed heritage stonework, for example—you can measure the rate and pattern of weathering precisely. Software can overlay successive scans and colour-code the areas of material loss, showing exactly where the stone is deteriorating and how quickly.

This data is invaluable for conservation planning. Instead of subjective assessments (“the carving is deteriorating”), you can provide quantitative data (“the exposed western face has lost an average of 0.8mm of surface material over the past three years, with the acanthus leaf tips losing up to 2.5mm”). This precision helps heritage managers prioritise conservation spending and make informed decisions about intervention timing.

I spoke with specialists in this space who work on data analysis and AI applications, and their perspective on using measurement data for predictive maintenance resonated strongly with my stone conservation work. The principle is identical—measure precisely, track changes over time, and intervene before small problems become large ones.

Practical Considerations

For stone carvers and masons considering 3D scanning, here are the practical realities.

Learning curve. Photogrammetry software is genuinely complex. Expect to spend several weeks learning the workflow and producing your first usable results. Laser scanners are somewhat easier to operate but the data processing still requires skill.

Equipment cost. A camera capable of good photogrammetry (any decent DSLR or mirrorless camera) costs $1,500-$3,000. Photogrammetry software is $200-$4,000 depending on the package. A handheld laser scanner suitable for stone work starts at about $15,000.

Processing time. A complex photogrammetric reconstruction can take 4-12 hours of processing time, depending on the number of images and the desired resolution. Laser scan processing is generally faster.

File sizes. Detailed 3D scans produce large files—hundreds of megabytes to several gigabytes. Storage and backup need to be planned for.

It doesn’t replace skill. This is important. 3D scanning is a tool. It provides better information. But the actual restoration work—cutting stone, carving detail, matching texture and patina—still requires a trained mason’s hands and judgement. The scanner tells you what shape to make. It doesn’t tell you how the chisel should feel against the grain, how deep to undercut a moulding, or when to stop refining.

The best restoration work I’ve produced has combined digital precision with traditional craft. Neither alone is sufficient. Together, they produce results that honour both the original stonework and the technology available to preserve it.