My dad told me how he made one once when he was much younger out of a scrap piece of glass. I took him a week using fine sand and water by the river, to grind down by hand.
One of his many stories, he also made a contact printer as well. My favorite of his tales is how he constructed his own quartz radio out of random parts, and how he strung up a complex antenna array on the roof of his house to get reception from around the world. All by reading instructions from books.