I am more certain we are talking “carbon in the cracks” after more tests. even down to 8 pews to get all the way through the paint the more layers of paint the better as the more carbon the better, but the paint holds the temps up so no paint will not leave much of a mark at no pews.
However I think if you try the sharpy trick on the under darkened tests it will darken up like any other tile,
Well at least we have a new method. And I think if you have the time to spare, you get a more durable image. And white spray paint isn’t very expensive. Not as cheap and just using a sharpie, but still pretty cheap. 
The other thing is that sharpie is not archival so it will fade over time and in sunlight. I think the next test will have to be to stick a tile with this white paint method in the sun and see how lightfast it is.
Found the source.
Thanks for finding that. All I could remember was that it was called the Norton White Tile Method. I knew I saw it on facebook somewhere and just made a mental note to try it. So once I had bought some supplies to try it, I brought it here.
I think black paint is an alternative to sharpie but more a pain to do. In the end it is not so different as it is still doing the same process with smaller cracks. If we used a binder like Gum Tragacanth and Boric acid and a safe mineral colorant it would be really different. as it would have a chance to bind to the material and show a color. Cobalt carbonate at less than 0.01% will make an intense blue.
There are also glass paints but traditionally they are high in lead, though nonlead is possible, @Jules might want to try a bit of her medicinal silver as long as the rest is safe,
Interesting that it says
"AIR ASSIST.. will reduce “Blacks” (but on some Co2 Lasers you will need air assist to keep lens clean)"Definitely lends credence to the carbon in cracks theory.
I was going to try this paint because of the carbon content.
Also going to try a black tile with the white paint. just to see what happens.
Latest score test,
With my setting of 200 speed it took around 35 mins to complete this single line. 
There were many point in the print where it would have been cool to stop because of the patterns that were showing.
Close up shot of previous tile with the wood pattern.
Love the spirograph! I would have to see it in person almost to be sure but it looks like carbon overflowing in the divots as that is where it can hold on.
In glassblowing the hot glass is often sprayed with copper or silver nitrate and then reduced in the fire. When light enough the silver makes a nice yellow and copper an orangy red, as it gets heavier they become the shiny metal color but I don’t think the glaze ever gets hot enough to melt before spalling instead. Boric acid could make a glass alone and might leave a surface that could react to the chemistry and bind to the glaze but I can think of nothing else that would have a chance of not damaging the machine.
The non-spiro test graphic has a great atomic age/mid-century vibe.
Just another score test. Focus height set to 0.500" so defocused off the tile 0.213". Speed set to 100, power from top to bottom starting at 10 and going up by 10. Except for the last line that i had accidentally set the speed to 250 and power full. groves are deep and filled with fractured black glass
so a quick wipe with paint thinner and this pattern will be gone.Edit: I would not recommended doing the line test. it is very bright and I worry about the reflections damaging the laser.
Agreed. When I was playing with tile, I only used dithering.
My tile experience:
First attempt with 340 LPI, speed 250, power 25
I think the last one has the perfect settings. The first two were from photos I had taken so they are lacking in good quality. The last was a very clear .png which certainly helped with the outcome.
The paint used is Rustoleum flat white from Home Depot.
really, the most important secret about engraving photos on anything is the part most people overlook.
a good quality original.
crisp focus, good contrast. anything less and you’re going to be working really hard in a photo editor to create that quality, which is never as good as a good source image.
there’s a reason JB’s stuff looks good. it’s partially due to experience manipulating photos, but i’m pretty confident he never starts with a bad or mediocre image.
… and understanding what makes a good source image while shooting means you end up with more usable images.
Exactly. And if you want to use non-optimal source material… make sure you maximize the blacks and white levels. Make sure that the blackest thing you have in your picture IS black. In the case of the dogs for instance, the noses, darkest shadows… adjust levels so those are black. Then get rid of any of the highs by blowing out the white levels on things you don’t need/want.
At least that’s how I do it. Mileage may vary.
Indeed. I’m going to have to pull out the tiles (I have 3 cases somewhere back when I was doing sets of them for the submariner reunion but finding them…ah that’s the challenge 
) The Norton method seems like a nice alternative to the sharpie & magic eraser technique.
This is my first real attempt. I did some minimal testing, and zeroed in the settings. I still have horizontal lines in the design–I thought I would eliminate those with more LPI (450, my initial tests were at 270), but they still showed up. The paint is not the cheapest, but it isn’t the most expensive, either. I think it was about $4.50/can. Rustoleum brand.
I’m pleased with how it turned out, and will keep trying this method. It works better than I expected, which was that I would spend about $15 on materials that would never really be used. To my pleasant surprise, I will do this again, though at 450 LPI, this took about 3:15.
I wonder if those horizontal lines are from a dirty belt or drive gear.
