I found some slate coasters on the bargain shelf at Jo-Ann the other day, and tried laser engraving them. The results were pretty good! See the photo gallery below.

I first tried vector engraving some text. This worked nicely. The engraved line was wider than we usually see on wood or acrylic, but that just made the letters more legible. Full power and full speed seemed to work as well as anything. Slowing it down just made the letters look a little sloppier, without making them much deeper. It also noticeably warmed up the whole coaster.

My first raster engraving test was again at full power and full speed, at the lowest resolution (252 dpi). It successfully changed the color of the surface, except for a few tiny spots that were still black. It didn’t create any relief I could feel, though, just a subtle texture change. Turning the speed way down did create lots of relief, and I ended up choosing a setting midway between those two for a moderate amount of relief. Fine interior details were squeezed out by the greater effective line width; that could have been compensated for in the artwork.

This material reacts to the laser in ways I haven’t seen before. When hit with vectors, some of the material seems to melt and form thin glass-like bubbles above the surface. They easily wipe away with a paper towel, exposing the carved letters. When hit with the raster, though, the excess material appears in the form of very fine white dust. Much of the dust is deposited on the surface. Because of the ventilation air flow, all the dust ends up toward the rear of the engraving. The dust is easily wiped off. I didn’t see any evidence of the dust getting into the laser’s optics.

Whether vector or raster engraved, the lasered areas are lighter in color than the rest of the surface. I don’t know exactly why. The black surface removed by the laser might be the result of natural aging, or it might be a factory-applied treatment. It might also have something to do with the rougher texture of the lasered surfaces. It will be interesting to see what color the engraved areas are after some time passes.

Since the laser always starts every job at the upper left corner of the rectangle that encloses the art, it’s not so easy to precisely place the laser head in the right place relative to the round coaster. To solve this problem, I created a simple jig. In CorelDraw, I added a vector circle around the outside of the raster artwork I wanted to engrave. I placed a piece of scrap material into the laser and engraved just the circle guideline on it. Then, without moving the laser head, I placed the coaster on top of the scrap and (after refocusing) centered it in the circle. I could then run the raster job and be sure the artwork would be lined up on the coaster just as I intended.

In fairly short order I was able to make a set of four coasters. With the simple jig the engraving is consistently centered so they look good even side-by-side.