If I ever take on glass engraving again, smack me...

[Robert Walters]

Opened the hood and it sounded like the glass broke. Looked down, there's all my engraving.

That sounds like thermal shock (and makes sense).

The glass is hot from being lasered, and the cooler ambient air hits it when you opened the lid and BAM, shatters at it's weakest points (where if was lasered).

I wonder if that's actually a "solution" to disappearing characters?
Give them a thermal shock using air or even a can of air (upside down?).

If it's a glass, I wonder if inserting ceramic wool during lasering would make a difference?

Is it possible that you could have been lasering BELOW the surface of the glass?
Microfracturing the sub structure, so there is a solid thin layer at the surface where the laser is going through, but not being effective, and the letters you do see are when the glass is still hot, and then "fuse" back together as it cools.

Maybe not focused correctly, maybe power setting too high/low.
I wonder if the surface of glass has been "hardened" (tempered) to help prevent simple chips in normal usage.

[Dan Hintz]

Robert,

You have to be going pretty darn slow to really heat up glass in the typical machines seen here (though I've done it in a failed attempt to etch the back of a glass tile). At the CO2 wavelength, the beam only makes it about 0.5mils into beyond the surface before being fully absorbed.

[Mike Null]

Put another way, you almost have to be trying to crack the glass to make it happen.

I've engraved a lot of tempered glass with zero problems.

But, if you engrave enough glass, you will have those missed spots Steve mentioned. Usually re-running the piece will solve the problem.

All things considered I'd rather sand blast or use my diamond burnisher on glass.

[Robert Walters]

Robert,

You have to be going pretty darn slow to really heat up glass in the typical machines seen here (though I've done it in a failed attempt to etch the back of a glass tile). At the CO2 wavelength, the beam only makes it about 0.5mils into beyond the surface before being fully absorbed.

I have no idea. Just sounded good in theory =)

If it's these "cheap" mass produced glassware, who know what the chemistry make up may be to make them cheaper to produce.

Kinda like that home brewed cermarc someone came up with using plaster of paris. Mineral chemistry is kinda voodoo to me, but damn cool imo =)

I know the laser is micro-shattering, but what glass makeup/process produces the best results I don't have the foggiest idea.

[Chuck Stone]

EDIT: I find the timing of this thread somewhat amusing considering I'm currently working on my book's chapter on glass processing...

Don't mis-spell our names in the credits..

[Martin Boekers]

The first order we got at my new shop for glass, someone brought in some of those stemless wine glasses from target. They are horrible for the disappearing text. Went through the whole job and it looked like maybe 3 or 4 letters showed up. Opened the hood and it sounded like the glass broke. Looked down, there's all my engraving. Scared the hell out of me.

Another issue is stemware with a slighty crooked stem, it's usually not
a lot but just enough.

I do a fair amount of black mirror from JDS, nice product, but yes, sometimes
the letters dissapear. I believe it's because when the glass fractured it
did it at such an angle the light reflects off it differently. It is engraved
and by tilting it slightly the letters are visible.

[Dan Hintz]

I know the laser is micro-shattering, but what glass makeup/process produces the best results I don't have the foggiest idea.

Let me put it this way... the (annoyingly persistent) idea that glass etches because it contains impurities, water vapor, and a myriad of other junk that the laser boils or heats to explosion is completely false. Whomever started that idea rolling probably guessed that's what was happening (and it's a reasonable guess if you choose not to pay attention to the science behind it), and ever since then I have seen it propagated not only in online forums but in print many times over (even in mags like A&E, Sign and Digital Graphics, etc.). Now it has become like one of those internet rumors that just won't die, an internet wive's tale.

I proved that notion false the moment I started placing high-quality glass, high-end optics, etc. into my machine and pulled out great, consistent etchings with zero chipping. I've even proven the whole "leaded glass is verboten" theory false. Details of what is truly happening will be in the book, and hopefully understanding what's really happening will help others create better engravings.

I know I've said it before but I'll say it again... if people can truly understand why the laser does what it does on every substrate, they'll be able to make logical leaps to new substrates that previously would have been unlikely.

[Kathy Madan]

Put another way, you almost have to be trying to crack the glass to make it happen.

I've engraved a lot of tempered glass with zero problems.

But, if you engrave enough glass, you will have those missed spots Steve mentioned. Usually re-running the piece will solve the problem.

All things considered I'd rather sand blast or use my diamond burnisher on glass.

I have never mastered the laser glass engraving thing either. We do almost all with the diamond burnisher. Even then we will find "hard spots" in the glass that the diamond simply will not cut thru on a single pass, sometimes in several passes. It is a total frustration to have perfectly clear engraving with just one missing letter. Sometimes I take my hand engraver to it, just to finish it off.

[paul mott]

Let me put it this way... the (annoyingly persistent) idea that glass etches because it contains impurities, water vapor, and a myriad of other junk that the laser boils or heats to explosion is completely false. Whomever started that idea rolling probably guessed that's what was happening (and it's a reasonable guess if you choose not to pay attention to the science behind it), and ever since then I have seen it propagated not only in online forums but in print many times over (even in mags like A&E, Sign and Digital Graphics, etc.). Now it has become like one of those internet rumors that just won't die, an internet wive's tale.

Dan,

When I look at some laser etched glass under the microscope I see hollow spheres, some broken some not. If they are not bubbles then what are they and how do you think are they formed ?.

Paul.

[Dan Hintz]

Paul,

I'll save the detail for the book (otherwise I'd be constantly cutting and pasting), but glass "etching" comes from localized surface tension. The laser heats up the surface of the glass to the melting (flow) point, and as the glass rehardens, the surface tension increases drastically in a localized fashion. Eventually the pressure is too much and the surface fractures, leading to the pits you're seeing under the microscope.

As I mentioned earlier, this is a surface phenomenon as the CO2 wavelength is absorbed completely within less than 0.5 mils (<0.0005") of the surface.

[paul mott]

Thanks Dan, I will have to study this some more.

Paul.

[Joe De Medeiros]

Paul,

I'll save the detail for the book (otherwise I'd be constantly cutting and pasting), but glass "etching" comes from localized surface tension. The laser heats up the surface of the glass to the melting (flow) point, and as the glass rehardens, the surface tension increases drastically in a localized fashion. Eventually the pressure is too much and the surface fractures, leading to the pits you're seeing under the microscope.

As I mentioned earlier, this is a surface phenomenon as the CO2 wavelength is absorbed completely within less than 0.5 mils (<0.0005") of the surface.

here's a quote from wiki.

But when a laser hits glass or stone, something else interesting happens: it fractures. Pores in the surface expose natural grains and crystalline "stubs" which, when heated very quickly, can separate a microscopic sized "chip" from the surface because the hot piece is expanding relative to its surroundings. So lasers are indeed used to engrave on glass, and if the power, speed and focus are just right, excellent results can be achieved. One should avoid large "fill" areas in glass engraving because the results across an expanse tend to be uneven; the glass ablation simply cannot be depended on for visual consistency, which may be a disadvantage or an advantage depending on the circumstances and the desired effect.

Some other info:
different glass formulas have different COE (coefficient of expansion) that's why some will mark better than others, Pyrex type glass has a COE of 32, where as typical window glass is around 82, Fusing glass comes in a few COE's 90, 96 are the most common, then there's the 104 used most to make lampworked beads, also very susceptible to thermal shock. The lower the COE the harder it is to mark, tempered glass does not alter the COE, it just aligns the structure to make it tougher. This all goes back to what Dan said about the surface tension, the higher the COE, the better chance you have of fracturing the surface, due to localized thermal shock. I have been working with glass fusion & lampworking for 11 years, as part of my art, and work with glass from 32 to 104 COE, I have also written a few pages on this for a science text book, on how art relates to science.

[Dan Hintz]

Joe,

Did you actually just quote a Wiki article as reliable info?

[paul mott]

I wonder if all Wiki articles are incorrect / inaccurate of just the ones that we don't actually agree with

(I once worked for a guy who said that all newspapers were politically biased so every day he bought two politically different newspapers, read both, believed what he wanted to believe from each and then thought he had the truth).

Paul.

[Belinda Barfield]

If I EVER think about taking a glass job to engrave, someone, please, do me the favor and smack the back of my head and ask "what are you thinking?".

Have I mentioned I hate glass?

I hate glass.

(where is that brochure for that sand carving setup????????)

OOOOH, pick me, Steve, pick me! I have the smack to head down pat, mainly because I smack myself so often for taking on jobs I should have refused. I have a glass job coming up in the next week or so for a wedding planner friend of mine.