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Fig. 4 | Heritage Science

Fig. 4

From: Micro fading test for textile single yarns: a new methodology applied to the Reformation Tapestry to assess its sensitivity to light

Fig. 4

Schematic representation of the light path with a glass slide interposed between the sample and illuminating/measuring probes. The upper glass slide has a thickness of d = 0.9 mm. n1 and n2 are the refractive index of air and the microscopic glass slide, respectively. ϑ1 is the angle formed by the normal to the surface and the receiving probe direction (45°); ϑ2 is the deviation angle inside the glass calculated through the Snell´s law. α is the complementary angle to the ϑ2 used to calculate the height necessary to the superimposition of the probes

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