Someday, people will find old printer ink cartridges and have no idea what they were used for. They are a part of the technology that I'm attempting to 'fossilize' under cloth. So I took a few of my tiles to Staples, asked for a manager, and showed him what I'm doing. And asked if I could please have some of those empty cartridges that they collect.
It was one of many times when it really helps to be a little old lady. Most people don't even see you (the power of invisibility!) and will happily give you what you want to get rid of you. So I took my bag of cartridges home, sawed them each in half and washed, and washed, and scrubbed all the ink out.
After I had tightly sewn the cloth over them, the black cloth didn't show enough detail. I took a round of wax and lightly rubbed it over the top....and it whitened the edges, just enough.