Hi Craig,
I don’t know if this image helps because there is not really a dot pattern as such to see.
The tile was produced from an 8 bit image using the Impact / Laser plugin and this fires the laser at up to 12,500 times per second so with a feed-rate of just 3,500 mm/min most of the dots appear on top of one another (overlapping).
The marking is essentially carbon soot which has, for the most part, been integrated into the surface glaze. I still have some different samples outside in the weather and what little sunshine we have had lately - whilst others have now had many dishwasher cycles so I am thinking the marking is reasonably permanent.
The lasering process will certainly destroy the surface integrity of the glaze but tiles are not usually glazed on their edges and I doubt that grouting compound is totally moisture resistant. But, like most of my stuff, it is early days yet and time will tell.
Tweakie.