Thread Count Analysis

Thread analysis in art conservation entails examining the threads in a canvas or textile to understand its weave structure and material properties. This analysis typically measures thread density based on averages drawn from a limited number of areas, for both warp (vertical) and weft (horizontal) directions.

Vincent van Gogh, Elimar, 1889, Saint-Rémy-de-Provence, oil on canvas, 45.7 x 41.9 cm, Inscribed lower right, “ELIMAR.” Owner, LMI Group International, Inc., SPV Number 0719 LLC.

An Advanced Methodology

Historically, thread analysis has relied on visual examination. While this approach provides an average thread count, it is inherently subjective and can be influenced by factors such as lighting conditions, magnification limitations, and human error. Additionally, it is limited to sampling, meaning only small portions of the canvas are analyzed, and it cannot offer a comprehensive view of the entire artwork.

In order to analyze the canvas weave of Elimar, we developed a more precise, objective method to enhance the accuracy of thread analysis.

Building on the work of the Van Gogh Museum's Automated Canvas Analysis Project, which relies on x-radiography, we developed a methodology that integrates specialized camera calibration, high-resolution visible light imaging, frequency domain analysis, and Radon transformation. This approach improves the resolution at which we can perform analysis, enabling accurate, non-invasive measurements of thread density and angle across the entire canvas.

Pre-Processing

Using visible light imaging technology, we captured every detail of the canvas at exceptionally high resolution. A calibrated target ensured accurate pixel density and magnification, while the image underwent a series of processing steps, from cropping the image to focus on the weave, to converting to grayscale to eliminate color distortions, and finally applying a high-pass filter to remove shadows and lighting inconsistencies. This enhanced the clarity of the thread patterns and allowed for precise analysis.

2.5 Million Frequency Captures

We use frequency domain analysis to ensure a comprehensive and representative sample across the entire canvas. The image is divided into overlapping 10mm square sections, each capturing thread density from various points across the canvas. This process resulted in the case of Elimar in a total of 2.5 million individual frequency captures, ensuring that both the horizontal (weft) and vertical (warp) threads were systematically analyzed.

Once the thread counts are gathered, statistical methods are applied to refine the data. Any outliers caused by thread irregularities or environmental factors are removed using the Interquartile Range (IQR) method, ensuring the data reflects the true thread density.

8,001 Angular Steps

To calculate the angle of the threads, we applied Radon Transformation, a technique that converts linear features, such as threads, into distinct peaks in a transform domain. By rotating the image, we align it with the threads which allows for precise angle measurement with sub-step accuracy. Using 8001 angular steps, this method was used to measure both the warp threads (ranging from -5º to 5º) and the weft threads (ranging from 85º to 95º), ensuring highly accurate thread angle determination.

Results and Thread Signatures

Thread Density:

Warp: 11.0 threads/cm
Weft: 10.4 threads/cm

Thread Angle:

Warp: 1.5º CW from North
Weft: -0.05º CW from East

The thread density analysis shows a warp density of 11.0 threads/cm and a weft density of 10.4 threads/cm, with slightly more vertical (warp) threads. The thread angles reveal that the warp is tilted 1.5º clockwise from North, while the weft is almost perfectly horizontal, deviating just -0.05º from East.

Building on earlier research that uses heat maps to visualize thread density and angle, we have developed this by accumulating values across rows and columns. This method creates an exceedingly detailed and robust thread signature against which to compare and differentiate artworks effectively.

Historical Comparisons

Our findings align with the SAFA report, which recorded an average thread density of 10 x 10 threads per cm across seven randomly selected and measured locations. Literature on other van Gogh paintings, such as Sunflowers, shows denser thread counts, with measurements of 11.5 x 17.2 threads per cm.

As detailed in the Elimar report, the process and analysis LMI undertook reveals variability and gaps in thread density data for van Gogh paintings, and a lack of comprehensive data makes it difficult to draw definitive conclusions about van Gogh’s canvas and other material practices across his body of work.

A New Benchmark for Thread Analysis

The pioneering methodology that LMI employed in analyzing Elimar marks a significant advance in thread analysis for paintings, offering exceptional precision, and transforming the ways we understand and study the canvas weave of paintings. Through its technology subsidiary, NC3, LMI will continue to enhance this technology and advance others in the arts and broader cultural heritage sectors.