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This is the setup for photographing prism tiles. It uses the same trick used to check glass flatness: observe a reflection in it.
		When trying to determine if old window glass is rolled (the early stuff) or float (the boring modern stuff), it's easier to distinguish them by looking at a reflection in the glass, rather than by looking at something through it. The distortion is much more obvious in a "bad mirror" than in slightly wavy glass, try yourself and see. Since a tile's front is mainly flat, the same trick is used: look at a reflection of something in it. This method also makes raised surface features stand out: embossing is easy to read and patterns are clearly visible over their entire area. A light box is suspended upside-down above the tile. Background is a piece of black velvet; anything neutral colored and light-absorbing would do, but always use the same thing. The camera looks down at the tile, at the reflection of the white-lit surface of the light box. Camera is clamped to shelf with a Clamper-Pod [defunct]; I couldn't get a tripod in the right position. Aperture, f 3.5, speed 1/50 As always, use a self-timer: hands off the camera when it shoots.