To be fair, if they first vocalize it they could just use Sparse Voxels which is my favorite differentiable rendering technique https://github.com/NVlabs/svraster

Resin, on one of these big expensive Stratasys machines: https://www.stratasys.com/en/3d-printers/printer-catalog/pol...

I remember seeing a 3d printer that was essentially a 2d printer which printed the surface and cut the outline and then laminated the sheets together which depending on the paper used would get you a block of something between mdf and plywood with high surface detail imagery.

I would imagine much the same approach could be done by laminating clear plastic sheets if you can maintain the transparencey without bubbles. It would get you modern colour printer resolution in two dimensions and sheet thickness in the other.

It wouldn't surprise me if some smart cookie could make a resin printer with a resin that sets in a state reflecting different wavelengths depending on how you zap it. That's a problem left for the reader.

You could easily release pigment into resin just before it gets hardened, but getting the right pigment to the right place would be hard, A print head zapping back and forth inside the liquid doesn't sound like it would be viable.

Printing in resin bottom to top part could allow a colour print head to fly over the surface printing a pigment layer then squirting the next layer of resin on top, zap and repeat.