Laser Engraving Crystal

[Pat Philips]

Hi Guys

I'm sure this question has been asked a lot of times, but I am having a lot of inconsistency with laser engraving Crystal, lots of shards etc..etc..

I know its the nature of crystal that is engraves poorly, does anyone have any tips on lowering DPI, less speed, more speed power etc...etc...

I have a Trotec Speedy 100,

Thanks in advance.

Pat

[Ross Moshinsky]

Crystal engraves fine. You just have to understand what's going on and why certain things work and certain things don't. I run my crystal at 500-600dpi, full power, wet packing paper, and slowish speed. On my 30W I ran 100% black. On my 60W, I run 80% black. Focus is very important, especially with a higher wattage machine. After I engrave a crystal or glass award, I very rarely have a shard or chip out. It happens on an occasion but it's rare.

I've found soaking wet packing paper to buffer the laser beam enough where I can run at a high DPI, which gives me the detail I want. Also the water keeps the crystal cool so I don't have to worry about chipping. Other people do run crystal completely differently. They run at lower DPI, always at 70-80% black, and dial the power and speed to work. Typically pretty fast with a good amount of power. I've tried this more than once as an experiment. I've never got consistent results. I think it heats up the glass too much at times which creates shards and the text lacks definition due to the low dpi. My method works for me on nearly all glass and crystal items with little issue.

My biggest issue with crystal is how inconsistent the awards are. They are absolutely terrible. They aren't remotely symmetrical which is a real issue and adds a significant amount of time into production time. Also the surface finish on them has gone down hill the last 2 years. 1 out of 4 will have a scratch. 1 out of 4 will be so out of spec I won't use it. Between the two I'd say I reject 1 out of 3 crystals awards. I wish the vendors and manufacturers would focus on quality a bit more. It's getting ridiculous how bad they are.

[Pat Philips]

Thanks for quick response Ross

Really appreciate that.

I have lowered my dpi to 500 and I am getting a much cleaner effect.

Could you clarify ? When you say 70-80 % Black, do you mean you are sending the artwork down as a lighter shade of black to get less power, why do you do this and not just adjust the power settings ???

I've read elsewhere people recommending this.

Thanks

Pat

[Scott Shepherd]

Could you clarify ? When you say 70-80 % Black, do you mean you are sending the artwork down as a lighter shade of black to get less power, why do you do this and not just adjust the power settings ???

I've read elsewhere people recommending this.

Thanks

Pat

It's different than lowering the power because lowering the power still lets the laser hit at full coverage. When you make it 70-80% black, it dithers the image, so you get tiny spaces between the firing of the laser, meaning less heat in that area.

[Tim Bateson]

I don't waste my time with wet paper towels or anything, except on thin champagne flutes (Liq dish soap) just place the award and laser it. I have even tried the glass laser tape - waste of money. If you are getting shards, you are using way too much Power/DPI and/or too slow of Speed. Glass/Crystal doesn't need high DPI for great quality. You only want to micro-fracture/etch the very outer surface. Trying to deep engrave doesn't produce better quality and mostly leads to glass shards and bad engravings.

Steve hit reply before I did. What he says about the shade of Black also applies to DPI. High DPI is the same as 100% Black. You need that dot spacing on Glass/Crystal for a quality engraving.

[Dan Hintz]

It's different than lowering the power because lowering the power still lets the laser hit at full coverage. When you make it 70-80% black, it dithers the image, so you get tiny spaces between the firing of the laser

^^^ THIS is the major cause of chipout. When you're packing laser hits in so tightly, you're increasing the chances that one fracture will connect with several other fractures surrounding it... enough that the immediate area is no longer solid but loose material only being held on by the jagged edges of surrounding pieces. Dithering the image by reducing the black level prevents such a high concentration of fractures, thereby reducing the possibility of loose pieces.

There is not enough heat build-up in the immediate area to be cause for concern, however, so I removed that from Steve's quote...

[Scott Shepherd]

There is not enough heat build-up in the immediate area to be cause for concern, however, so I removed that from Steve's quote...

Thanks for that Dan, I still struggle with not using "heat" as the term when talking about lasers. I know it's wrong, but it still makes sense in my head :)

I assume he's talking about crystal awards that are thick. Our experience with crystal was with wine glasses and it didn't go well. It was too thin and they were fracturing and causing weak points in the glass, so if you just lightly touched it to something else, like tapping glasses together, it would break at the engraving.

[Dave Sheldrake]

When I get stuck with a crystal engraving job (that I tend to avoid like the plague) I don't use co2/IR wavelengths, 532nm gives amazing results and at very low power too.

[Scott Shepherd]

When I get stuck with a crystal engraving job (that I tend to avoid like the plague) I don't use co2/IR wavelengths, 532nm gives amazing results and at very low power too.

Where do you get one of those wavelengths Dave? :)

[Ross Moshinsky]

I don't waste my time with wet paper towels or anything, except on thin champagne flutes (Liq dish soap) just place the award and laser it. I have even tried the glass laser tape - waste of money. If you are getting shards, you are using way too much Power/DPI and/or too slow of Speed. Glass/Crystal doesn't need high DPI for great quality. You only want to micro-fracture/etch the very outer surface. Trying to deep engrave doesn't produce better quality and mostly leads to glass shards and bad engravings.

Steve hit reply before I did. What he says about the shade of Black also applies to DPI. High DPI is the same as 100% Black. You need that dot spacing on Glass/Crystal for a quality engraving.

Someone's going to have to explain this to me. I've been in the industry for 15 years now. Why doesn't crystal need to be engraved at high DPI? If I engrave at 300dpi vs 500dpi, there is a visible difference in quality. The edges of the letters are not smooth. I'm not a big fan of the hatched look that comes with people using 70% black either, but I've found it somewhat a necessity with my higher wattage machine so I've compromised. To be perfectly honest, I find 300dpi engraving equally unacceptable to seeing minor but consistent chipping around letters.

[Tim Bateson]

...Why doesn't crystal need to be engraved at high DPI? If I engrave at 300dpi vs 500dpi, there is a visible difference in quality. The edges of the letters are not smooth. I'm not a big fan of the hatched look that comes with people using 70% black either, but I've found it somewhat a necessity with my higher wattage machine so I've compromised. To be perfectly honest, I find 300dpi engraving equally unacceptable to seeing minor but consistent chipping around letters.

I usually do use 95-100% Black, but lower DPI. Probably similar to 80% Black and Higher DPI. Which-ever, the objective is dithering or not to overlap dots as was stated by Dan/Steve. You are right about 300 DPI, but.... it does depend on the Graphics and Text being used. On Glass, I would be surprised if you can visually see any difference between 1,200 and 600 DPI. Besides the probable occurrence for shards at 1,200 DPI. Although rarely, I have even been as low as 200 DPI. I would say most are done at around 400 DPI.

I do hundreds of crystal awards every year for a local distributor. So, I have had a lot a practice at adjusting my settings and this for me produces the highest quality. As with any settings your mileage may vary as every machine is just different enough.

[Dave Sheldrake]

Where do you get one of those wavelengths Dave? :)

I have a 3d crystal engraver Scotty :) (one of the type used to make glass block trophys)

[Kev Williams]

A gal brought me a bunch of solid glass castings of miniature stair risers. With my Triumph cranked up it'll actually melt the glass as it engraves, no shards that way and the results are fantastic!

But guess what happens to a wine glass when I try that? ;)

With 3 different machines, I do know this: they're all different, and what works in one won't work in another.

F'rinstance, my 40w LS900's laser beam 'wobbles' as it rasters, each pass has rolling peaks & valleys. As rastering continues, some of those peaks overlap each other in some places more than others. One result of this is vertical banding. (BTW, it's not a mechanical issue. I can run a 25 LPI pass 20 times and the beam path is identical every time) The only fix I've found for this issue is less-than-100% black and PHOTO MODE. The dithering created by the software nearly eliminates the overlapping beam problem. The results I get engraving wine glasses are absolutely horrible in 'regular' mode, but almost perfectly mimic sandblasting at 80% black @ 400 lines per inch and 500 dots per inch. I've found no settings that work with 'regular' 100% black engraving. And for what it's worth, grayscale doesn't work either. Must be photo-mode.

Conversely, my 25w Optima (1997 Universal) never has had a banding or beam overlap issue at all. Running less than 100% black in halftone (there is no 'photo' specific mode with this software) isn't *usually* necessary. I say 'usually' because I hate the lack of control of the lines per inch (stupid throughput slider bar). However, I don't do much glass engraving in the thing because I don't have a rotator for it. But it does glass 'normally' 1000% better than the LS900 does...

Then there's my glass-tube Triumph. As noted above, I can get great results by roasting the glass, but otherwise I haven't had time to experiment to find a sweet-spot...

In summary, there's a reason why some machines like 70% black and others do fine just blasting away. We may be comparing apples to apples, but like apples, some are red, some are green, some yellow... ;)

[Dan Hintz]

When I get stuck with a crystal engraving job (that I tend to avoid like the plague) I don't use co2/IR wavelengths, 532nm gives amazing results and at very low power too.
Showoff... ;)


Why doesn't crystal need to be engraved at high DPI? If I engrave at 300dpi vs 500dpi, there is a visible difference in quality. The edges of the letters are not smooth. I'm not a big fan of the hatched look that comes with people using 70% black either, but I've found it somewhat a necessity with my higher wattage machine so I've compromised. To be perfectly honest, I find 300dpi engraving equally unacceptable to seeing minor but consistent chipping around letters.

As Tim mentioned, it's a tradeoff. 70% is definitely on the low side, IMO, for black level, but you're likely to get similar results with 100% black and 250dpi... not exactly, but similar. This is one of those times where a napkin-drawn picture would be significantly more clear than words, but I'll try.

The human eye is trained to look for edges and periodicity (i.e., patterns). It's why heavily compressed JPEG images look so awful... more edges, and they happen at a regular interval. When we're looking at designs on an award (for example), the text should appear crisp along the edges. But how do we achieve that with such opposing forces? Let's look at the two extremes, low dpi (with 100% black) versus low black level (with high dpi).

Low dpi, 100% black: Vertical/horizontal edges will look blah (such as the letters 'T', 'H', etc... I'm ignoring serifs and such) because despite the high black level, there are simply too few dots next to each other at a low dpi to create a non-jagged line. This will be severely amplified on curved portions (such as the letter 'O'). The pattern, however, will be periodic... close up it will have an almost scalloped appearance, but even at a reasonable distance it's noticeable.

High dpi, low black: Same situation as above in terms of overall appearance, but it's now due to a totally different reason. Lots of dots next to each other are possible, but the low black level means dithering comes into play and many of those dots will not get printed. Well-defined edges are now made of randomly-spaced dots... no discernible pattern, but now it looks fuzzy.

We know you can't do high dpi, 100% black for reasons mentioned earlier, and going the opposite way (low dpi, low black) would be a complete train wreck. So what's one to do?

Compromise... and this is material-based. For cheap soda lime glass (drinking glasses, picture frame glass, etc.), I usually go for lower dpi (250-333) and higher black (85-90%). For higher quality leaded glass/crystal, etc. I aim for higher dpi and somewhat lower black (75-85%). Experimentation on your part is advised.

If/when time permits, I'll come back and edit this description to make it more clear...

[Ross Moshinsky]

As Tim mentioned, it's a tradeoff. 70% is definitely on the low side, IMO, for black level, but you're likely to get similar results with 100% black and 250dpi... not exactly, but similar. This is one of those times where a napkin-drawn picture would be significantly more clear than words, but I'll try.

The human eye is trained to look for edges and periodicity (i.e., patterns). It's why heavily compressed JPEG images look so awful... more edges, and they happen at a regular interval. When we're looking at designs on an award (for example), the text should appear crisp along the edges. But how do we achieve that with such opposing forces? Let's look at the two extremes, low dpi (with 100% black) versus low black level (with high dpi).

Low dpi, 100% black: Vertical/horizontal edges will look blah (such as the letters 'T', 'H', etc... I'm ignoring serifs and such) because despite the high black level, there are simply too few dots next to each other at a low dpi to create a non-jagged line. This will be severely amplified on curved portions (such as the letter 'O'). The pattern, however, will be periodic... close up it will have an almost scalloped appearance, but even at a reasonable distance it's noticeable.

High dpi, low black: Same situation as above in terms of overall appearance, but it's now due to a totally different reason. Lots of dots next to each other are possible, but the low black level means dithering comes into play and many of those dots will not get printed. Well-defined edges are now made of randomly-spaced dots... no discernible pattern, but now it looks fuzzy.

We know you can't do high dpi, 100% black for reasons mentioned earlier, and going the opposite way (low dpi, low black) would be a complete train wreck. So what's one to do?

Compromise... and this is material-based. For cheap soda lime glass (drinking glasses, picture frame glass, etc.), I usually go for lower dpi (250-333) and higher black (85-90%). For higher quality leaded glass/crystal, etc. I aim for higher dpi and somewhat lower black (75-85%). Experimentation on your part is advised.

If/when time permits, I'll come back and edit this description to make it more clear...

This is the premise I reject. My point really is that you can absolutely tell the difference between low DPI and higher DPI engraving and statements suggesting otherwise are misleading. Crystal can be engraved at 500-600dpi and there is a distinct difference between that and 300dpi engraving.

At this point I don't mind laser engraving crystal because of the process. I have my process down. I've grown to really dislike it because the product is near crap. At least that's the case from JDS and PDU.

[Dan Hintz]

This is the premise I reject. My point really is that you can absolutely tell the difference between low DPI and higher DPI engraving and statements suggesting otherwise are misleading. Crystal can be engraved at 500-600dpi and there is a distinct difference between that and 300dpi engraving.

I didn't say, or even suggest, that there is no difference between low- and high-dpi engravings. My statements are in reference to reducing chip out in a manner that still allows for a quality image.

Engraving at high dpi and 100% black runs a high risk of chip out. It's not guaranteed, and a high-quality crystal certainly helps in that regard... but if you were to try that with soda lime glass, I have a shiny new nickel that says you have multiple chip out areas. Nature of the beast. You could lower the power to the bare edge and reduce chip out, but are you really fracturing at every dot you were before? Unlikely, which means the process is little different than using dithering or reduced dpi.

[Ross Moshinsky]

I didn't say, or even suggest, that there is no difference between low- and high-dpi engravings. My statements are in reference to reducing chip out in a manner that still allows for a quality image.

Engraving at high dpi and 100% black runs a high risk of chip out. It's not guaranteed, and a high-quality crystal certainly helps in that regard... but if you were to try that with soda lime glass, I have a shiny new nickel that says you have multiple chip out areas. Nature of the beast. You could lower the power to the bare edge and reduce chip out, but are you really fracturing at every dot you were before? Unlikely, which means the process is little different than using dithering or reduced dpi.

I really understand. The disconnect is you're replying to something I directed towards Tim. Your reply went into the practical theory of engraving crystal which is very important to mention to someone new. But it doesn't really address his statement which was that you don't need to engrave crystal at a high dpi. That statement implies that there is no real difference in quality between lower and higher dpi engraving, which I regard as misleading to put it nicely.

As for glass vs crystal, the biggest issue I've come across is focal point changing. If I get out of focus because of the inconsistency of the product, I'll get chipout. Otherwise, my process is very consistent. I won't say it's perfect, because it isn't. I just find that if I get a chippy piece, 9 times out of 10 it's because the focal point has changed.

[Tim Bateson]

I stand by my quote "On Glass, I would be surprised if you can visually see any difference between 1,200 and 600 DPI."... and also "You are right about 300 DPI, but.... it does depend on the Graphics and Text being used."

My customer uses mostly PDU and I can't recall any chip outs/shards in the past several years. I do have the usual micro-fracture of glass that needs to be cleaned out of every engraving, but no chip outs. I will try to find some photos tonight, but I doubt that I have anything to show great detail - this customer frowns on me taking pictures as they feel I may compete with them for their end customers. No chance of that, this is easy money - drop shipped here, I engrave, they pickup, then mails me a check.

[Keith Winter]

I agree with Ross inconsistency in the glass is the main cause of chip-out. It's the nature of the beast. Ross said it perfectly here:



As for glass vs crystal, the biggest issue I've come across is focal point changing. If I get out of focus because of the inconsistency of the product, I'll get chipout. I just find that if I get a chippy piece, 9 times out of 10 it's because the focal point has changed.

As to the argument of 100% vs 80% black I throw my hat in with the 80% black folks. Seems to help control the fracturing.

[Tim Bateson]

Just as a side note - I get more broken crystal upon delivery from PDU than I do from JDS.