Sinter is what you’re looking for…
That’s the process going on here. It’s not to the point of melting, rather bonding at the molecular level.
Sorry but no I can’t see why glaze, which you say is a liquid glass, would not melt with sufficient heat. Heat is applied to make glass molton when used in glass blowing, so would it not react the same under the intense heat of a lase. Maybe it’s just my 85 year old brain can’t think clearly. All the same this is not really the place to hold a discussion on such technical matters. So I’ll accept your superior knowledge on the process of tile engraving.
My take on it would be staining the glaze. Kind of like spilling red wine on a white carpet. Sure, you get harsh enough chemicals you can get it out, well probably just most of it.
Whether “glaze = glass”, melted or sintered, or whatever… I don’t know. You folks are far more up-to-date and technically strong than me, an old man (though 9 years behind Ron at only 76 
). But I can show you what I’ve done and how I did it… even if I can’t be entirely technically correct in describing what’s really going on.
The same NWT process on ceramic tile can be used on transparent window-pane GLASS. Painted (here using Krylon flat-white spray paint)…
and, after cleaning with acetone, a fused-to-the-glass black image…
By contrast, painting with black paint (here, poorly applied tempera) and all else (power, speed, etc) being the same, the lasered image is etched (ablated?) into the glass…
Ultimately my interest is in the end product… not so much, whether I can accurately, technically describe what is going on to make it happen. So I can’t argue my position (and don’t want to try) but I can show what can be done…
Though the “recipes” are functionally similar, I know there’s a definite difference in what’s technically going on “underneath”… the black image is a raised (embossed?) image on the surface and the frosted image is a relieved (ablated?) image in the body proper of the glass.
Again, no argument here, one way or the other. Just my observations… and my $0.02.
– David
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True, but it’s the whole thing… Try heating up a glass bottle and attaching a handle on it without heating all of it …
Glass is a poor conductor of heat, when you heat a portion of it up, that part expands and the other doesn’t, so it cracks or shatters. This is how a co2 laser engraves glass, it shatters it. The uneven heating shatters the glass.
I take mine and run steel wool over them to ensure they don’t end up in someones hand or worse.
If you could melt it, you could cut it… You’ve never poured something hot into something glass and have it shatter?
@dkj4linux … Your laser cannot directly engrave glass, you are using an indirect method of engraving glass by heating something in near proximity and that heat damages the glass… You can do the same with putting something black under the glass, lase through the glass… You’ll have to flip the image since it will be on the back side.
The black image is just TiO2, again, molecularly bound to the glass.
Jack, I’m not sure why you are so insistent that we understand we can’t melt or cut glass with a laser… or why we can’t directly engrave glass with our lasers. But that’s not what we’re trying to do here, either. This thread IIRC is about using the NWT method – an indirect method – to engrave tile… and Ron’s “recipes” for using “raw” TiO2 rather than commercially available white spray paint.
I’m also aware of the no-paint, thru-the-glass, method… check it out in my thread.
– David
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Preach, brother!
This is not true.
We are not melting any glass (glaze) only TiO2.
Seems like you keep bringing it up 
I stand corrected, Jack. I apologize for my ignorance and technical inaccuracy.
No perspiration
Dear David/Ron
Thank you for the quick reply. I will definitely try again this week.
Just to double confirm. Is it OK I apply 2 or 3 coats of Ti02 on the ceramic tile surface.
I also have a Neje A40630 7.5watt Diode Laser and may try to use this instead of N40640. Will definitely sent photos of my finish work and hope it’s what I want and also to make sure both you and Ron are happy and have not wasted your time for the recommendations.
Thank you. John.
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Dear Ron
Thank you for your advice and quick reply. I’m working now and engraving is my hobby.
I will sent you information requested in your reply during the week when I have time.
Thank you again, very kind of you and David.
John
John you and any others that have followed this thread are more than welcome to my help, be it technically right or wrong, at least it has created some interest. When I first started out on this hobby there was little advice available and I learned by trial and error. I now see loads of people making a living by producing YouTube videos on the subject and many of them contain misleading inflammation. I personally enjoy trying to improve how we do things by the old “suck it and see” method. Hence the reason for starting this thread in the first place. I think it’s now known as experimenting.
Dear Ron / Jack
Hope you both are having a great weekend. I tried testing again and Ron as requested I have attached screen shots of Material Test Generator which I hope is what you want to see. I’ve also wash off the TiO2 done earlier and re paint one layer on fully dried ceramic tiles also.
Using my Neje N40640 I’ve also attached my settings and photo of engraving result as recommended by Jack. I’ve not wash the tile yet because the end result is bad. I think my Lightburn setting is incorrect but cannot figure out what is it.
Please see attached. Hope you all can help and tell me what settings to make to do ceramic tile engraving. Thank you. John
Hi David
Sorry I send email earlier to Ron and you but instead of putting your name. My sincere apologies. Jack is also one of the guys that have been helpful in the Forum.
Anyway I did follow you recommendation to change the speed and power to do laser engraving but the result is not good. See attached. Th photo showing engraving ceramic is not washed yet.
Thank you John
John have you tried this test grid that I use? Run it as is on your machine and let us see the results. I’m sue you will get something worth evaluating.
Material Test Grid.lbrn2 (137.6 KB)
Thank you Ron. I cannot open “Material Test Grid.lbn2” from my office computer. I should do it via the computer where I use LightBurn software correct. Thank you.
Hi Ron. It’s me again. Can you kindly confirm if the screenshot is correct section I have to go in to get what is required. Sorry I’m not very good with software usage and mainly use for operation when I’m in the correct place. Thank you.
John, just click on the file I sent. Then in the dropdown panel click open file. Close the forum and you should see the file already loaded into lightbruns work space. Place your material on the laser bed and press start. Don’t change any of the settings I need to see what result you get using the file as I have set it.
Material Test Grid.lbrn2 (137.6 KB)
This is what you should get. NOTE high power and low speed can give the reverse of what you would expect. So select the square to your requirements and read off the speed and power settings that produced it.
Dear Ron
Thank you. So it’s following your Speed and Power settings to do test. I’ll definitely try it when I have time or over the weekend.
Thank you
John