Glass Engraving with Glowforge: The 7-Point Quality Check I Use Before Every Order

Who This Is For (And When You Should Use It)

If you're engraving glass with a Glowforge—especially if you're selling the results—this checklist is for you. I put this together after the third time I had to explain to a customer why their "personalized" wine glass had a ghosted image that looked like it was done in 2014.

This isn't a theoretical guide. It's the 7-point check I run on every single glass item before it goes on the machine. Takes about 4 minutes. Has saved me an estimated $2,300 in wasted materials and re-dos over the last 18 months.

Point 1: Confirm Glass Type & Coating

Not all glass is the same. I learned this the hard way when a batch of supposedly "laser-safe" drinking glasses from a new supplier shattered on the first pass.

The check: Look for a small stamp or marking on the bottom. If it says "tempered" or "heat-strengthened," put it aside. Tempered glass can crack unpredictably under thermal stress from the laser.

What I use instead: Standard soda-lime glass—the cheap stuff you get at thrift stores or bulk suppliers. I also avoid anything with a painted or metallic coating unless I've tested a sample first. That "gold rim" you see on fancy wine glasses? It's not gold; it's painted. The laser will burn it off unevenly, and you'll get a smudged, brown mess.

Quick tip: Scratch the bottom edge with a utility knife. If it scratches easily, it's soda-lime. If it doesn't, it might be tempered or borosilicate (which handles heat better but engraves differently).

Point 2: Clean the Surface Properly

I used to think wiping with a dry cloth was enough. It's not. Fingerprints and dust act as diffraction points—they scatter the laser beam, and the engraving comes out uneven, especially on curved surfaces.

My process: Wash with warm water and a mild dish soap (Dawn works well). Dry with a microfiber cloth—not paper towels, which leave lint. Then do a final wipe with isopropyl alcohol (70% or higher) on a lint-free wipe. Let it air dry for 60 seconds.

One thing I check: The alcohol shouldn't leave streaks. If it does, you didn't get all the soap off. Rinse and repeat.

Point 3: Test the Rotary Attachment Alignment

The Glowforge Rotary Attachment is a great tool, but it's touchy. If the glass isn't seated perfectly level, the engraving will be skewed. I've seen this happen on a $90 order of 20 beer mugs—all of them had the text running uphill on one side.

The check: Place the glass in the attachment and rotate it manually through a full 360 degrees. Watch the surface—if it wobbles more than about 2mm at the engraving zone, adjust the end cones. Most issues come from the glass slipping during the job, not from the initial setup.

My fix: I use a small strip of painter's tape on the glass where the drive roller contacts it. It adds friction and stops the slip. (Should mention: this only works if the tape is clean and adhered firmly—no air bubbles.)

Point 4: Set the Correct Focus (This Is Tricky)

On flat material, Glowforge autofocus works fine. On curved glass, it doesn't. The default autofocus assumes a flat surface, so it'll focus on the center of the curve, not the edge. The results? The center is crisp, but the edges are soft and fuzzy.

What I do instead: I use the manual focus tool that came with the machine. I place it on the glass surface at the point where the engraving will start, then lower the head until the tool just touches. Then I check the opposite side. If the distance is different, I split the difference. Roughly speaking, if the curve is moderate, focusing for the midpoint of the engraving area works.

Don't hold me to this—but I've found that on a standard 20oz wine glass, setting the focus about 3mm higher than the autofocus gives the best result across the full curve. I'm not 100% sure why, but I think it's because the beam cone creates a wider effective focal zone.

Point 5: Choose Your Engraving Settings (Speed vs. Power)

This is where most people go wrong. They crank the power to get a deeper engraving, but on glass, high power can cause micro-cracking. The engraving ends up looking chalky and rough, not smooth and frosty.

My baseline settings for standard soda-lime glass on a Glowforge Pro:

• Speed: 450 (out of 1000)
• Power: 80 (out of 100)
• Passes: 1

I start there, then adjust based on the glass thickness. Thicker glass (like a 12oz mug handle) can handle slightly more power—try 85. Thinner glass (like a shot glass) needs less—try 70.

A note on line art vs. filled areas: For clean text or thin lines, speed at 480 works better because the laser doesn't dwell long enough to cause heat buildup. For filled areas or solid logos, drop speed to 400 and let the laser do multiple passes if needed. One deep pass is worse than two shallow ones.

Point 6: Run a Test Engraving (Small—I Mean Small)

I know you don't want to waste material. I get it. But I've had too many experiences where the settings looked perfect on paper and the result was garbage. The test is the cheapest insurance you can buy.

What I do: I engrave a 1-inch square in the least visible spot—usually the bottom curve of the glass, near the base. I use the same settings as the final job, with a small geometric pattern (a few crosshatched lines and a circle). Then I check for:

• Even frosting (no patchiness)
• Clean edges (no blurring)
• No micro-cracks (look under bright light)

If the test looks good, I proceed. If not, I adjust power by +/- 5 and speed by +/- 20, then test again. Usually takes two tries. That's 10 minutes of test work to avoid a $30 ruined glass and the cost of reprinting packing materials.

Point 7: Final Inspection Before Packing

This is the one people skip because they're excited to ship the order. I've almost done it myself—or rather, I have done it, and then had to send a replacement at my own cost.

My inspection checklist:

• Light test: Hold the glass up to a bright light. If the engraving looks "whitish" or has a blue tint, the laser was too hot and may have caused subsurface damage.
• Touch test: Run your fingernail across the engraved area. It should feel slightly rough but not catch. If it snags, the power was too high and the glass might chip later.
• Consistency test: Look at the engraving from a 45-degree angle. The frosting should be uniform. If you see bands or stripes, the rotary attachment might have been slipping.

One more thing I check on the final glass of each production run: The last piece often gets rushed because I'm mentally already done. I always inspect the final piece as if it were the first.

Common Mistakes (And How to Avoid Them)

1. Using too many passes on glass: I know people say "multiple light passes give a better finish" for wood. On glass, multiple passes increase the risk of heat buildup and crazing (tiny surface cracks). If one pass looks light, increase power by 5-10%, don't add a second pass.

2. Ignoring the smell: When you're engraving glass, you should smell a slight "mineral" or "burnt rock" odor. If you smell burning plastic, you might be hitting a painted coating or a contaminant. Stop, clean, and re-inspect.

3. Forgetting to turn off the air assist: On some Glowforge models, the air assist can blow small glass particles into the engraving area, causing scratches. I turn it down to 50% for glass—enough to clear debris, not so much that it becomes a sandblaster.

4. Not accounting for the curvature when using a design: Text around a wine glass will look distorted if you don't use the Glowforge's cylindrical correction feature. It's in the software under "Artwork Settings" → "Wrap." I've forgotten this exactly once. The customer sent a photo. I won't forget again.

Final Thought (I'm Not a Fan of Sentimental Endings)

This checklist sounds like a lot of work. It's not—once you're used to it, it's just part of the workflow. The time you lose on verification is nothing compared to the time you lose on rework.

If you take away one thing: check the glass type first. Tempered glass, painted glass, coated glass—they all look similar and behave very differently under the laser. I keep a box of labeled samples on my shelf. Before I put anything on the Glowforge bed, I compare it to a known-good sample. That simple step has eliminated about 70% of my glass engraving failures.

Settings listed are based on Glowforge Pro firmware version 2.3. Power and speed recommendations tested on soda-lime glass sourced from a bulk supplier in Q1 2024. Your results may vary. Test first.