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.

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.

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.

Figure 3.

Figure 4

Figure 4.

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.

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

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Mechanical Wear on Ancient Ceramics

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.

Mechanical Damage on Ancient Ceramics

Mechanical Damage: Root damage