I posted earlier this week about abrasion holography, a hologram technique that uses a network of simple arc shaped scratches to encode a visible, 3D hologram into a chunk of plastic. Carl was the first to comment on exactly what was on a number of peoples minds:

This is just crying out for someone to generate complex pictures using CNC.

Like many great ideas, someone has already worked this one out! William Beaty was kind enough to write back with a link:

The scratches need to be be almost perfectly smooth with no jaggies at all. Normal CNC doesn’t work, but a couple months ago Evan at found that “drag engraving” does reduce the jaggies enough.

The photo above is Evan’s cube, engraved on blackened copper. The top image is what you see in normal diffuse lighting. The bottom is one perspective of the hologram when viewed head-on under a point-source light. Evan writes:

The way this type of hologram is generated is to start with a 2d representation of the subject (the cube in this case). Then an arc is drawn using a point on the visible vertices and edges of the shape. A set of closely spaced points along all visible edges is then used to provide the anchor points for the radii of the arcs. The reason the image isn’t perfect appearing is because of slight inaccuracies in the placement of the arcs (my fault) and some waviness in the copper plate which is only 26 gauge material.

There are a lot of creative possibilities with this one. First person to engrave a HACKS hologram on a copper business card wins a standing ovation.

Synthetic Holograms With a CNC Mill – Link
DIY Hand-Drawn Holograms – Link