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Based on your mention of electricity, and of a "welding rod", I will assume you are talking about arc welding. From Lincoln Electric: "Arc welding is one of several fusion processes for joining metals. By applying intense heat, metal at the joint between two parts is melted and caused to intermix - directly, or more commonly, with an intermediate ...


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I guess it's because it's easy to add all sorts of materials that make the surface absorptive for a broad spectrum such as for visible light. Then it'll look black. To write on a black paper you need something that really covers the paper adding material which reflects all visible light, causing a white color. As far as the human eye and its dynamical range ...



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