Fig 1.
Measurement of the three-dimensional shape of cracks on the surface of artworks through OCT and analysis of the evidence that can be used for authenticity judgment.
(a, b) OCT system set-up to measure the crack area of the artwork. This system can fix artworks on the stage to prevent unwanted movement while the artwork is being evaluated. The stage moves them in units of at least 10 μm along the XY-axis and the focused beam on the crack area to accurately measure the desired area. (c, d) Acquired 3D data of art objects and (e, f) cross-sectional images extracted to compare the width and depth parameters of the original and forged artworks.
Fig 2.
Original oil painting (a, b, and c) and counterfeit works (d, e, and f). They were prepared for an analysis of the three-dimensional forms of cracks used for authenticity identification of art works. The forgeries were completed by checking the color combination of the original work, the artist’s brushstroke style, and the thickness of the paint layer as much as possible.
Fig 3.
Images of Artwork 1 (a, b) and Artwork 2 (c, d) showing the area selected by the OCT system and enlarged views of the cracks in each area. The cracks were selected because the paint characteristics of each work were prominent. They were then analyzed with the OCT system. Enlarged images of original cracks (a’, b’) and fake cracks (c’, d’) at the selected location in Artwork 1 and Artwork 2.
Fig 4.
Comparison between the cross-sectional characteristics obtained from the cracks in the original artworks and the counterfeit cracks using the OCT system.
(a) Cracks in Artwork 1 caused by the small amount of medium in the upper layer but formed with a wide rectangular shape. The forged cracks in Artwork 1 appear similar in depth to the original cracks, but unlike the original cracks, which are rectangular, they have an inverted triangle shape. (b) Original cracks in Artwork 2 caused by the small amount of medium in the under layer. The cracks were formed in a thin and very deep rectangular shape. Unlike the original cracks, the forged cracks in Artwork 2 are very shallow in depth. (c) Quantitative analysis of the OCT cross-section images of the original and forged cracks of Artwork 1 and Artwork 2. The representative values of the dimensions of the original and forged cracks selected for analysis, were compared by (d) width, (e) depth, (f) width/depth, and (g) depth/width.
Fig 5.
Images showing the location of cracks in (a) the original and (b) forged oil paintings. The enlarged images of cracks selected as the OCT measurement area in (a’) the original artwork and (b’) the forged artwork. In various areas of this artwork, cracks were created by (Ⅰ, Ⅱ) canvas aging, (Ⅲ, Ⅴ) paint layer drying, and (Ⅳ) physical impact on the layer. The forged cracks were created considering the characteristics and causes of the original cracks.
Fig 6.
Comparison between the OCT cross-sectional images of (a) the original and (b) forged artworks for art authentication. (c) Quantitative analysis of the OCT cross-section images of the original and forged cracks of Artwork 3. The representative values of the dimensions of the original and forged cracks selected for analysis were compared by (d) width, (e) depth, (f) width/depth, and (g) depth/width. (Ⅰ) Cracks caused by the aging canvas made in areas covered in a thin layer of paint. (Ⅱ) Cracks caused by the aging canvas made in areas where the paint layer was relatively thicker. (Ⅲ) Cracks caused by the drying paint layer and made in areas with a thin layer. (Ⅳ) Cracks made by applying a physical impact to the paint layer. (Ⅴ) Cracks caused by the drying of the paint layer and made in area with a thick layer. The side paint layer of the forged cracks protrudes and has a much shallower inverted triangle shape than the original cracks.