Best Practices For Engraving Glass

Typically you want to use as little power as possible to make a mark — kinda like when doing edge lit acrylic.

The laser beam doesn't actually ablate the glass; it creates microfractures in the glass when the water molecules are converted to steam. The spalling usually occurs due to too much power.

Glass varies a lot (as do most substrates) so you may have to sacrifice a piece or two to get the settings dialed in right. Also, the cheaper the glass the better it engraves typically (cheap glass has a higher moisture content, among other things, which lends itself to higher contrasting engraves). Glass has more water content so when the laser hits the water molecules, they turn to steam and expand 1000x (explode), which causes the microfractures.

How CO2 Lasers Interact With Glass

When engraving glass with a CO2 laser, if you get fracturing and chunks coming out, that's an indication of too much power usually.

CO2 cannot ablate glass like it can other things, so it makes microfractures in the glass and looks frosted. The water molecules in the glass are heated by the laser and turn to steam and expand 1000x, so tiny explosions at the molecular level cause the frosting.

These fractures should never be aggressive enough to cause the glass to delaminate and spall. Higher speed, lower power, very low air assist, and defocus a few mm to 'soften' the beam. Also make sure your line interval isn't too high or it basically just engraves parts that have already been engraved and blows it out.

Settings Video (Nova 63-130)

Here is a video with settings for a Nova 63-130:

Masking, Soap, and Other Techniques

As far as masking, soap, etc. — this is an attempt to mitigate the spalling and chipping that happens, but spalling is a symptom of not using the correct settings for the material most times.

Below is an example of severe spalling and delamination (the darker areas of the engraving).

And, if you have it dialed in right, none of that is needed — just a quick buff with fine steel wool to knock down any 'burrs'.

Glass Types and Compatibility

There are lots of types of glass. Borosilicate glass, like Pyrex®, does not engrave well with a CO2 laser.

Other engineered performance glass, and glass with different tempers, all have vastly different properties and may not lend themselves well to CO2 laser engraving.