I’ve been wanting to try engraving a glass mirror. I picked up several 2-inch round mirrors from the craft store for a test.

You could engrave from the front, which would be the same as engraving any kind of glass. You’d get a frosted effect. But what I wanted to try was engraving the back, through the metallized coating that turns a sheet of glass into a mirror.

For my first attempt I guessed 10 power and 100 speed, and that turns out not to be enough. It cut through the protective coating, and into the metal layer, but not through the metal. Interestingly, the metal layer appears to be copper colored from the back. I’m guessing that the white metal (do they still use silver?) reflective layer is very, very thin and copper is plated on top of it for protection.

Increasing the power to 30 created the effect I was looking for. It was immediately obvious that it was cutting through the metal, because the laser lit up the entire piece!

In the video you can see that I used some masking tape folded over to attach the mirror to a piece of scrap wood. Without the tape, the compressed air blast from the laser head was enough to float the mirror out of alignment. I engraved a circle on the wood to help me place the mirror accurately.

The final result is a little hard to visualize from a photograph, but it looks really cool in person. Sparkly! In the photo you can see the reflection of my rose gold iPhone (camera) in the parts of the mirror that are still mirror. The engraved parts appear frosted white.

Here’s what it looks like from the back:

The dark blue is the protective coating, which you can see has been removed in many places where the metal is left intact. It would probably be a good idea to re-coat the engraved mirror to keep the metal from corroding. Also, the edges are sharp, so some kind of mounting for it (or grinding the edges smooth) would be a good idea.

There were many fascinating things shown at San Diego MakerFaire recently. One of them was an Epilog laser cutter. Epilog is a U.S. brand that commands a significantly higher price than the Full Spectrum Laser we have, which is based on an imported Chinese product. Epilog lasers are known for doing very fine engraving. At MakerFaire, they were cutting and engraving a demonstration file, and handing them out, so I grabbed one. It was a detailed raster-engraved Aztec calendar about 2.1 inches in diameter, on 1/8-inch prefinished alder wood from LaserBits. I ordered the same wood (I think), found the same file online (minus the text), and tried to reproduce it on the Colaser.

Once I got the settings close, my results were actually pretty close to the Epilog sample.

I’m not sure why the engraved parts are darker on my version than on Epilog’s. Mine also needed wiping off after engraving, whereas the Epilog sample came out of the machine pretty clean. Comparing the detail closely, you can see that the Epilog held the finest detail a little better.  It’s possible I could do better by more fiddling with settings. Maybe reducing both power and speed would work better.

This kind of detail is only possible with high quality wood. This 1/8″ alder is about $10 a square foot, if you order it in 6×12-inch sheets from LaserBits. It’s much nicer to work with than any of the plywoods I’ve tried.

Here are all my attempts.

The bottom one was under powered, and the two in the middle row were done at too high a power setting: the laser engraved right through the wood. I found that the raster power setting was quite non-linear, which is why it took so many tries. The setting I liked the best was 33 power, 100 speed.

Engraving a highly detailed design all the way through makes a really cool filigree effect.

This design would be too fragile, but with some attention in the design to including a support structure, this would be sturdy enough for some purposes.

If your job looks like this, either you’re trying to cut some thick material that’s beyond the capability of our laser, or else you have chosen your settings poorly. This kind of burning generates a lot of smoke and flying embers, which can contaminate the optics and lead to expensive repairs. If you see this kind of result, please STOP right away and rethink your job.