There’s an irony to the idea that glass could be a currency in a world covered in sand. But all glass is not created equal.

Glass is valued based on purity: the clearer and more brilliant the glass, the more it’s worth. The investment of skills, tools, and time required to create pure glass is formidable to say the least, and so the highest grades—those used for things like jewelry, palace windows, or suneater devices—are rarely seen in possession of the general population.

One application of high-quality glass is for spectacles, which are as much a means of vision correction as they are a status symbol. Spectacles are an icon of affluence and respect—and thus, it’s not uncommon to see the poor fashion lensless, ‘false’ spectacles to create, if only at a distance, the illusion of wealth.