Modify a CNC mill to carve into a wet clay tablet, for example, to draw a QR code. Fire the clay tablet, and then you have data preserved in a medium that is known to be able to last thousands of years.
Should the mill simply poke the clay, displacing clay around the indentation? This seems easy, but the displaced clay might disturb adjacent pixels. What should be done if some displaced clay sticks to the poking tool? Perhaps clean after each poke.
Alternatively, should the mill remove a small amount of clay for each indentation? This seems better but mechanically more difficult and messy.
How difficult is it to get the initial clay surface flat enough to make fine markings with the mill? Alternatively, do some 3D scanning to start with a depth model of the not-quite-flat blank tablet. This of course is what human scribes did, impressing cuneiform into only approximately flat clay tablets. Humans do depth perception visually and with pressure sensing. Will the wet clay change shape during the time it takes to carve it?
Wet clay is messy. It might be easier to start with a hard material and use a mill in the traditional way. What hard material will last at least as long as clay? Of course, fired clay, i.e., ceramic, is one possibility, but is it too brittle to mill?
Laser etching or laser engraving ceramic is another possibility. We would want to actually etch the ceramic and not just the glaze, because ceramic is what known to last a long time. Can laser tricks (i.e., focusing) engrave ceramic beneath the glaze without disturbing the glaze? If etching away the glaze first, or engraving unglazed ceramic, what is the best way to apply a protective coating afterward? Maybe just glaze again.
Laser engraving glass is another possibility. Internal engraving, i.e., bubblegram, is intriguing, as it protects the data from wear and offers the possibility of 3D encoded data. How would one read such data?
Instead of mechanically carving a material, also consider photolithography. What substrates work and will last as long as clay?
3D printing is also an alternative to milling. What materials last as long as clay?
Clay is attractive because it is basically dirt, so it is very inexpensive compared to probably anything else. Aluminum and glass are probably the most compelling long-lasting alternatives.
Can the clay tablet have a shape which protects it from damage? Of course, the thicker it is, the less likely it is to break. Maybe a lip or rim around the sides will protect from abrasion.
Slight variation:
Instead of carving data directly into a medium, carve a stamp or die which can then be used to print many copies of the data, perhaps with ink or pressing into another medium, e.g., clay or a softer metal. Previously.
One way to create a stamp of a QR code is with movable type, where the only two "letters" (sorts) are the white pixel and black pixel. Manually assembling a stamp from pixels would be tedious but movable type has always been tedious. After creating a stamp, suppose testing reveals an error. Can the error pixel be fixed without having to disassemble and reassemble the entire stamp?
Can movable type be automated? If so, it is an alternative to the CNC mill.
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