Bubblegram

A bubblegram (a.k.a. laser crystal, 3D crystal engraving or vitrography) is a solid block of glass or transparent plastic that has been exposed to laser beams to generate three-dimensional designs inside. The image is composed of many small points of fracture or other visible deformations and appears to float inside the block.

Each point is created by a laser beam focused to high intensity at that location by a computer-controlled opto-mechanical system. A complex or highly detailed image occupying a 5 cm (2 inch) cubic volume typically requires the creation of tens of thousands of such points.

Bubblegram images may be created by intersecting laser beams in appropriately doped plastic to induce a chemical reaction via heat or photonic excitation, creating bubbles or nodes where the plastic has a different index of refraction.

Glass block bubblegrams of Russian origin entered international commerce as a novelty in the late 1990s, but high prices and the predominantly simple, inartistic subject matter severely limited market penetration. In the early 2000s, a much less expensive, more visually appealing and highly diverse array of Chinese-made bubblegram novelties achieved wide commercial success in the United States, to the extent of becoming a fad: representations of monuments, corporate symbols, religious imagery, mythical creatures and nature scenes appeared in gift shops across the land.

There also exist companies which will take custom photographs of people, convert them to a heightmap, then render that as a bubblegram memento.

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Wikipedia