Glowforge Engraving Glass: What Works, What Doesn't, and How to Clean That Lens

I'm a quality compliance manager at a small manufacturing company. I review every laser-cut or engraved item before it ships—roughly 800 pieces a month. In 2023 alone, I rejected about 12% of first deliveries because of spec issues. So when I bought a Glowforge for our engraving work, I brought that same picky mindset.

This isn't a tutorial that assumes everything works perfectly. It's a checklist for getting clean engravings on glass with a Glowforge, based on about 200 hours of testing and a few expensive mistakes. There are six steps, and one of them—the one about the lens—is the one most people skip. Don't skip it.

Before You Start: Does This Apply to Your Project?

This checklist is for engraving images, text, or logos on flat or gently curved glass items—think wine glasses, drinking glasses, mirrors, and flat panels. It's not for cutting glass (laser cutters can't cut glass) or for deep carving. If you need deep carving or 3D effects in glass, you need a different process entirely.

I've tested this with both the Glowforge Pro and the Glowforge Aura. The steps are the same for both. If you're using a third-party laser like a Boss or Epilog, the principles still apply, but the settings will differ.

Step 1: Pick the Right Glass

Not all glass engraves the same. I learned this the hard way when I ran 20 identical designs on 20 different glasses from a thrift store haul. Maybe five came out looking good. The rest were blotchy, cracked, or barely visible.

Here's what I've found works best:

• Clear, uncoated glass with a smooth surface produces the most consistent white frosted engraving.
• Colored glass works, but the contrast might be lower depending on the color. Dark green and dark blue are particularly tricky.
• Frosted glass can work, but the results are less visible because the glass is already diffuse.
• Glass with coatings (like some drinking glasses with a shiny, metallic-feel coating) may not engrave at all, or the coating might peel or discolor.

If you're not sure about a glass item, run a test on a small, hidden area first. The bottom of the base is usually a good spot.

One more thing—avoid glass with bubbles, seams, or visible inclusions. Those weak points can crack under the heat of engraving (more on that in Step 5).

Step 2: Clean the Glass (More Than You Think You Need To)

This seems obvious, but I can't tell you how many times I've seen a reject because someone skipped this. Glass handling oils from your fingers are enough to cause uneven engraving.

Method:

• Wash the glass with warm water and dish soap. Rinse thoroughly.
• Dry with a lint-free cloth or microfiber towel. Paper towels can leave fibers.
• Wipe the engraving area with isopropyl alcohol (70% or higher) on a lint-free wipe. This removes any remaining oils.
• Let it air dry completely before placing in the Glowforge. Alcohol residue can leave a faint mark.

I use these steps every time, even if the glass looks clean out of the box. It takes 2 minutes and saves a lot of frustration.

Step 3: Apply Transfer Tape or a Damp Paper Towel

This is the controversial step. Glass has a reflective surface that laser beams don't like. The laser can bounce off the glass and back into the machine, or simply fail to leave a mark because the energy is reflected away.

The most common solution is an interface layer. Two options I've tested:

Option A: Transfer tape (the pros' choice). Apply a piece of transfer tape—the same stuff used for vinyl decals—over the area to be engraved. The laser burns through the tape and marks the glass. The tape also helps reduce heat stress on the glass surface. After engraving, just peel off the tape. This gives the cleanest, most consistent results I've seen.

Option B: A damp paper towel (the budget hack). Lay a damp (not soaking) paper towel over the glass. It needs to be fully flat and in contact with the surface. This does reduce reflections and can help distribute heat. However, I've found the results are less consistent, and you have to be careful about the towel drying out or curling up during the engrave.

I use transfer tape for production runs. I've used the paper towel trick for one-off gifts. It works, but it's not as reliable.

Step 4: Set the Right Glowforge Settings

Here's where a lot of people end up with burned-in marks or barely-visible frosting. The Glowforge default settings for glass are a good starting point, but I've found they need adjustment for most real-world glass.

My baseline settings (Glowforge Pro, 100% power, speed 1000):

• Engrave: 100% power, speed 800 — This gives a distinct white frosted finish on most clear glass.
• Lines per inch (LPI): 270 — Lower LPI can look too heavy; higher LPI can look too faint. 270 is the sweet spot I keep coming back to.
• Number of passes: 1 — You almost never need more than one pass. Two passes can cause excessive heat buildup and cracking.

If your results are too faint, try slowing down the speed to 700 or 750 before increasing power. If the engraving is too heavy (looks burned or has a dark center), try increasing the speed to 900 or 1000.

I always run a small test on the bottom or on a scrap piece of the same type of glass first. Write down the settings that worked. I keep a notebook (yes, a physical notebook) in my studio for this.

Step 5: Manage the Heat (The Cracking Prevention Step)

Glass cracking during engraving is the number one reason items get trashed in our quality review. The laser heats a tiny, concentrated area. If the glass expands there and the rest of the glass doesn't, you get a crack.

How to prevent it:

• Pre-warm the glass — Not on the Glowforge! Set the glass on the machine's own heating bed (if it's already warm) for 5-10 minutes first. Or just let it sit in a warm room (above 70°F / 21°C). Cold glass is much more likely to crack.
• Engrave thin designs first. If you're doing a large solid area, the heat will build up. Start with thinner lines or small text to warm the glass gradually.
• Work in sections. If your design is large, break it into multiple smaller engrave jobs with a few minutes' cool-down in between. On the Glowforge UI, you can just run the same job on different areas of the bed.

I've cracked three wine glasses and one mirror before I learned this. The mirror was a $80 piece of furniture. Now I pre-warm everything for at least 10 minutes.

Step 6: Check and Clean the Glowforge Lens (The Step Everyone Forgets)

Here's the step I've learned the hard way. Your lens gets dirty over time, especially when you're engraving glass. Glass engraving creates debris—tiny glass particles and vaporized coating material—that settles on the lens. A dirty lens scatters the laser, which means:

• Your engraves get weaker and less consistent (you need more power or speed to compensate)
• Your designs lose detail (the edges blur)
• Your glass is more likely to crack (uneven energy distribution)

I went through a period where my glass engravings were just getting worse. I couldn't figure out why. I changed settings, changed glass types, cleaned the glass more carefully... nothing. Then I remembered a Glowforge support article I'd skimmed months ago: check the lens.

How to check: Most Glowforge models have a lens you can inspect. Open the access panel, and look at the lens. If you see dust, debris, or a cloudy film—clean it. (Glowforge has an official guide for this, and the specific type of cleaning solution they recommend is important—don't just use any glass cleaner, as some can damage the lens coating.)

After I cleaned my lens for the first time, my glass engraving quality jumped back to where it had been when the machine was new. The issue wasn't the settings or the glass. It was a $10 cleaning kit and 5 minutes of my time.

I now inspect the lens every 20-30 hours of operation, especially after glass engraving jobs. It's not hard, but it's easy to forget.

What to Do When It Doesn't Work

If you follow all six steps and still get poor results, here are the three most likely culprits:

1. The glass is coated. Some modern glass (especially from discount stores) has a very thin protective coating that the laser can't penetrate. Try engraving on the bottom or under a label for a few seconds. If nothing happens, it's coated.

2. The lens is still dirty. I've seen lenses that looked clean to the naked eye but were still compromised. Use a bright light and magnification to check.

3. Your Glowforge needs calibration. This is less common, but if you've had the machine for a while or it's been moved, the laser beam might be slightly off-axis. Glowforge support can walk you through a calibration test.

Honestly, most problems I've seen come down to the lens or the glass type. If you start there, you'll save a lot of time and glass.