Exploring the Surface of Ancient Ceramics: Photogrammetry

The Surface of Ancient Ceramics

Ancient ceramics have been a significant part of human history for thousands of years, with the mass production of properly fired ceramics across the Levant taking place from the early bronze age through to the present day. The diverse range of clay recipes and firing techniques used throughout these periods makes it difficult to generalize these ceramics as a whole. Moreover, the treatment and "storage" conditions of these ceramics since their firing, as well as their treatment upon rediscovery, have a significant impact on the surface characteristics of the artifacts.

The preservation of ancient ceramics varies greatly, with some ceramics having been ground to dust over time, while others have been excellently preserved under abnormally good conditions. Even when the preservation appears equivalent between two ceramic pieces, they may have been stored in entirely different ways and thus suffered different types of damage. This damage can range from exposure to underwater environments, mechanical damage from being underground and surrounded by roots, to chemical damage from the leaching or absorption of substances such as calcium from the surrounding soil or water. In some cases, a single ceramic piece may have suffered very different types of damage, such as having one side partially buried in the soil while the other is exposed to air. The potential scenarios are virtually infinite.

Exploring the surface of ceramics is an interesting and challenging task, as visual examination, even with specialized tools, can only reveal so much. It is very difficult to conceptualize the surface in one's mind when forced to look at the colored surface of the ceramic, which may mask or accentuate details that do not exist. Scanning technologies are therefore desirable, as a 3D model allows the viewer to choose the lens through which they view the object and can eliminate distractions such as color and lighting. Although scanning technologies have advanced significantly in recent years, their use is still extremely limited, with most high-accuracy systems costing tens of thousands of dollars to achieve sub-millimeter precision consistently.

Photogrammetry Introduction

Photogrammetry is a technique that allows for the creation of 3D models from a series of photographs taken from different angles. This non-contact, non-destructive method has gained popularity in recent years due to its accessibility and affordability compared to traditional 3D scanning methods. By capturing a large number of overlapping images and using specialized software to analyze and match features across the photographs, a detailed 3D model of the object can be generated.

In the context of archeological ceramics, photogrammetry offers several advantages. First, it allows for the capture of high-resolution surface details without the need for expensive specialized equipment. Second, the non-contact nature of the technique ensures that fragile artifacts are not damaged during the scanning process. Finally, the resulting 3D models can be easily shared, analyzed, and manipulated digitally, enabling researchers to study the surface characteristics of the ceramics in great detail without the need for physical access to the artifacts.

The ability to study ceramic surfaces remotely through photogrammetry has significant implications for the field of archeology. Researchers can collaborate and share findings more easily, regardless of geographic location. The digital preservation of artifacts also ensures that their surface details can be studied for generations to come, even if the physical objects deteriorate over time. Furthermore, the interactive nature of 3D models allows for a more immersive and engaging experience for both researchers and the general public, potentially sparking greater interest in the study and appreciation of ancient ceramics.

Our Photogrammetry Setup

Our research employs a carefully calibrated photogrammetry setup designed to capture high-resolution images of ceramic artifacts. The core of our system consists of a Sony A7cII camera equipped with a Sony 35mm F1.8 lens. This combination offers a balance of image quality and versatility suitable for a wide range of ceramic sizes and shapes.

• Camera: Sony a7cII (33 megapixels, 7008 x 4672 pixels)
• Lens: Sony 35mm F1.8
• Working Distance: 25cm to 75cm from the subject
• Resolution Range: 9-27 pixels per mm, depending on distance

At the closest working distance of 25cm, our setup achieves a resolution of 27 pixels per mm, allowing for the capture of fine surface details. For larger artifacts, we can increase the working distance up to 75cm, still maintaining a respectable 9 pixels per mm resolution.

To ensure consistent, high-quality images, we use a powerful 400W flash with a custom polarizing filter. The camera lens is cross-polarized to reduce unwanted reflections, which can interfere with the photogrammetry process. This lighting setup allows us to capture clear, well-lit images even of challenging ceramic surfaces.

Each artifact is photographed from 100 to 350 different angles, depending on its size and complexity. A motorized turntable ensures consistent spacing between shots. After capture, images are post-processed in Adobe Lightroom to optimize exposure, reduce highlights, and maximize shadow detail. This step is crucial for enhancing the visibility of surface features.

The processed images are then fed into Reality Capture, a photogrammetry software that constructs the final 3D model.

While our current setup produces excellent results, there's always room for improvement. For even higher resolution, especially for smaller artifacts or extremely fine surface details, we could consider the following upgrades such as a higher resolution camera, for example a Sony A7rV (60.2 megapixels, 9504 x 6336 pixels) could increase our maximum resolution to 37 pixels per mm at 25cm. A specialized macro lens, such as the Sony 90mm f2.8 macro lens, focusing at 28cm, could dramatically increase our resolution up to 62pixels per mm with the a7cII or a staggering 85pixels per mm on the a7rV

While capturing the images, we make sure to capture the object from many angles. Due to using a turntable this produces a set of orbits around the object with a consistent angle between each image.

An example can be seen in this animation, where each pyramid represents a camera position and angle.

Through this methodical approach to photogrammetry, we are able to create highly detailed, accurate 3D models of ancient ceramics. These models serve as valuable resources for studying and preserving the intricate surface characteristics of these artifacts, providing insights into their manufacture, use, and post-depositional history that might otherwise be difficult or impossible to discern through traditional methods of examination.

Surface Pitting and Wear of Free Field Jug

Surface pitting is a common form of degradation found on ancient ceramic artifacts. It occurs when the surface of the ceramic is exposed to various environmental factors over time, leading to the formation of small, shallow depressions or cavities.

While many archeological pieces have surface pitting, and arguably all do to some extent, we present here an extreme case of surface pitting on a Cypriot Iron Age free field jug.

To highlight the surface textures we will present a series of images with false colors aimed at aiding the visualization of the surface details. The false colors are generated from the normal map of the 3D model, which encodes the surface orientation of the object. This allows us to enhance the visibility of surface features such as pitting, wear, and other forms of damage. Often times a true color image will be presented alongside, we invite you to compare and contrast.

In Figure 1 we show the base of a jug which has old inventory and catalogue labels attached. This is purely for demonstration purposes to provide an example of this false color view.

Figure 2 gives us a front-view of the jug, showcasing extensive pitting damage alongside its entire height and front.

Figure 1. Base of ancient Cypriot free field jug, showing old labels, demonstrating photogrammetry view.

Figure 2. Front portion of ancient Cypriot free field jug showing extensive pitting damage to the surface.

The damage appears very evenly spread across the front, and taking in the close up view of Figure 3 we can appreciate this in more detail.

When archeological ceramics suffer uneven surface pitting or damage, it usually indicates the orientation of the object during burial. In this case, the jug was likely partially buried in the soil, with the exposed portion experiencing more wear and pitting than the buried portion. The opposite could also be true if the pitting is due to submersion damage.

Figure 3.

A side view such as in Figure 4 allows us to see the stark contrast in pitting damage between the two halves of the object. It is an incredible shame that the extensive damage is also confined to the only areas with decoration. This jug is our popular Free Field Goat & Anthropomorphic Date Palm Jug.

Figure 4.

The extent and patterns of surface pitting can provide valuable insights into the burial conditions and post-depositional history of ceramic artifacts. By studying these features through photogrammetry, archeologists can gain a better understanding of the complex interplay between the artifacts and their environments over time, this can help us understand the processes that shape the degradation of artefacts in-situ.

Large Oinochoe in Excellent Condition

Ceramics come in all forms of preservation, and while some may be heavily damaged, others can be in excellent condition. In this section, we present a large oinochoe with excellent surface conditions.

This Oinochoe is rather large, at 32cm. It is a Cypro-Geometric jug likely from 1050 to 750 BCE though later dates up to 580 BCE are also possible.

The Jugs surface is incredibly clean, indicating a potentially harsh chemical treatment may have been used. Acid wash treatments were extremely common throughout the 1900s up until the early 2000s. Archeologists and institutions avoid acid washes in favour of mechanical or careful spot-acid application with barriers.

The concretions and mineral deposits left on the surface have been removed by the acid wash, and while on visual inspection the jug looks to be in excellent condition, the acid wash may have removed internal minerals and altered the structure of the ceramic.

However even such a well-preserved piece will have suffered significant surface damage upon closer inspection.

The photogrammetric analysis reveals a more nuanced picture of the oinochoe's surface condition. While the ceramic appears to be in excellent shape at first glance, the false color rendering highlights subtle imperfections and irregularities that are not immediately apparent to the naked eye.

Mechanical Wear on Ancient Ceramics

Cypriot ceramics are almost all from burial contexts, and as such have limited wear from use. However, mechanical wear can still occur from the burial environment itself. Roots, rocks, and other artifacts can rub against the ceramic surface, causing abrasions, scratches, and other forms of damage.

In this case we can see a scrape tearing through the slip of the jug revealing the structure of the clay beneath.

Similar damage can be seen here, as well as one large concretion or other deposit still remaining on the surface.

A side view allows us to better understand some deeper pitting damage that was not as visible from visual inspection.

A different jug reveals mechanical damage and potential restoration marks with a large gash across the surface that is almost invisible in the true color image.

Studying mechanical wear patterns on ancient ceramics can yield important information about the artifact's life history. The orientation and distribution of scratches and abrasions may indicate how the object was handled, stored, or transported in antiquity. In burial contexts, these marks can also provide clues about the nature of the surrounding soil matrix and any disturbances or shifts that may have occurred over time.

Furthermore, identifying and documenting mechanical damage is crucial for conservation purposes. By understanding the types and extent of wear present on a ceramic surface, conservators can develop appropriate strategies for stabilization, cleaning, and restoration. Photogrammetry provides an invaluable tool in this process, allowing for detailed, non-invasive examination of surface features that might otherwise be difficult to discern or record.

Photogrammetry models also allow conservators and future archeologists to establish the current state of an artifact, providing a baseline for monitoring changes over time. By comparing successive scans, researchers can track the progression of mechanical wear and other forms of damage, helping to inform decisions about conservation treatments and long-term preservation strategies.

Chemical Damage on Ancient Ceramics: Surface Concretions

Ceramics are porous materials that can absorb substances from their environment over time. The environmental conditions in which these ceramics were stored for the many years since their creation can have a significant impact on their surface characteristics.

One of the most common forms of chemical damage observed on ancient ceramics is the formation of surface concretions. These concretions appear as hard, often crusty deposits adhered to the ceramic surface. They can range in color from white to brown and may cover small patches or extend across large areas of the artifact.

The primary cause of these concretions is the leaching of minerals, particularly calcium, from the surrounding soil or water. Over hundreds or thousands of years, groundwater can slowly dissolve calcium-rich minerals in the burial environment. As this calcium-laden water permeates the porous ceramic, the minerals precipitate out of solution, forming crystalline deposits on and just beneath the surface. This process is exacerbated in soils with high calcium content, such as those rich in limestone or shell.

The growth of calcium concretions involves complex chemical interactions between the ceramic material, the dissolved minerals, and environmental factors such as pH, temperature, and moisture levels. The distribution and thickness of the concretions can provide insights into the artifact's burial conditions and post-depositional history.

In this example of a Cypriot Iron Age barrel jug we can see extensive concretions covering the surface of the artifact.

Removing concretions is a delicate process that requires the expertise of trained conservators. Mechanical cleaning methods, such as scraping or abrasion, risk damaging the fragile ceramic beneath while chemical cleaning techniques such as the use of acids can damage the artifact in other ways.

In some cases, conservators may choose to leave the concretions in place, as they can provide valuable information about the artifact's history and may even help to stabilize the ceramic. However, if the concretions are causing active deterioration or obscuring important surface details, careful removal may be necessary.

Photogrammetry plays a crucial role in documenting and studying surface concretions on ancient ceramics. By capturing high-resolution 3D models of the artifacts before and after conservation treatments, researchers can better understand the extent and nature of the chemical damage, as well as the effectiveness of different cleaning methods.

Furthermore, the ability to digitally manipulate the photogrammetry models allows for detailed examination of the concretions from various angles and under different lighting conditions. This can help to reveal subtle surface features and patterns that might be difficult to discern through traditional methods of examination.

Conclusion

Photogrammetry offers a powerful, non-invasive tool for exploring the complex surface characteristics of ancient ceramics. By capturing high-resolution 3D models of these artifacts, researchers can study and document various forms of damage, such as surface pitting, mechanical wear, and chemical concretions, in unprecedented detail.

The ability to digitally manipulate and analyze these models provides valuable insights into the burial conditions, post-depositional history, and conservation needs of ancient ceramics. Photogrammetry also enables the creation of detailed, interactive visualizations that can engage both the scientific community and the general public, fostering a deeper appreciation for these fascinating artifacts and the stories they tell.

As photogrammetry techniques continue to evolve and become more accessible, we can expect to see even more exciting applications in the study and preservation of ancient ceramics. By embracing this technology, archeologists and conservators can unlock new avenues of research, collaboration, and public outreach, ensuring that these irreplaceable artifacts continue to shed light on our shared human history for generations to come.

We hope to continue our photogrammetry initiative and share the optimal setups we develop over time. We believe that even with the user of limited consumer technology, cutting-edge results can be achieved with the right knowledge and techniques.