I made some trivets with simple images on the cheap home center plain white tiles in another project.

Simply put, this black on the tile is as good as a glaze, it is actually part of the glaze and will not scratch or chip.

Some more info on how I got there.

My equipment is an "Ortur Laser Master 3", a 10W optical power diode laser. The power levels used were <50% so even a 5W laser can do this.
I use Lightburn and I am fascinated by the capabilities of everything this software can do. This type of lasing is one of the simplest things that can be done.

There is a 30 day full-feature trial available to road test. $60 for a year of updates, then you are frozen at the latest version (and all earlier versions) but still can use it at that version (and lower) forever without further charges.

On to the test!

Titanium Dioxide (TiO2) is the colorant in lots of stuff, primarily white paint. From what I've gathered, TiO2 is actually a jet black mineral but when turned to powder it reflects/refracts light to appear Snow White. The laser melts the powder back into black (queue AC/DC).

The challenge is to somehow apply this black to a glazed tile.

The laser will fuse (melt) the TiO2 with the tile glaze. Too little power (heat) and the TiO2 will turn black, but not adhere to the glaze. Too much heat and you'll start burning a pit into the tile and evaporate the TiO2.

The first  goal is to coat the tile with the TiO2.

Two approaches, Make your own method to apply TiO2 powder (available on Amazon and everywhere else), or use some paint with enough TiO2 already Included.

Kilz primer is a good source and for this test I'm trying out Rustolium "2X" white primer.

Some  6"x6" white tiles for the test, about $0.30 each.

Step 1: Good cleaning of all the fingerprints, snot, and everything else found on items bought from a public store.
Acetone works!

For the Rustolium test, I applied 3 good coats with about an hour of drying between and overnight after all coats applied

I noticed that this primer flakes easily off the slick glaze so handle with care.

The mix-your-own TiO2 powder method

The powder doesn't like to stay suspended in most solvents, so a carrier is needed. There is a method developed (or at least championed)
called the "Norton White Tile Method".

He used ordinary PVA glue to help keep the powder in suspension and as a bonus, the excess "paint" after the lasering can be removed with just water. The Rustolium needs solvent to remove.

Another fellow (Ron Clarke) has further developed a recipe:

The soap releases any surface tension and lets tiny bubbles pop.

What I found out is it needs more TiO2 powder.
Use TB I or some non "waterproof" glue or you'll defeat the ability to rinse off with plain water

I mixed up the above, but then added about another 50% more TiO2. I then thinned it out with more water until it was slightly thinner than latex paint. Stir the crap out of it for several minutes to get all the powder in suspension and all clumps broken up.

I use the tip of a foam brush to apply (light touch).

Four coats, hour dry in between with alternating up/down and right/left brush strokes. Some people add a touch of food coloring that contrasts with the tile so they can see any missed or thin areas.
Personally If I was preparing a bunch of tiles I'd explore spraying it on for ease and consistency.

So now we have two test tiles, Rustolium and home-brew mix. In the long run the home brew its a lot cheaper than the paint and washes off with water.

On to finding the correct laser power and speed.

Lightburn has a built in grid test that lets you create test squares at a range of power and speed.

Into the laser! You will want a small amount of "air assist" which is some airflow down the barrel of the laser to keep backsplash from getting on the lens and keep the smoke out of the beam.

The result straight out of the laser:

The lower row at 5mm/second speed actually burned a pit into the tile after about 25% power (1.5 Watts - 5 Watts tested).

A quick compressed air cleaning and a brush off removes the dust for a better view

In the diagonal between the upper left light area and lower right dark area, you can see some vertical "streaking". This is where the powder mix thickness was uneven due to brush strokes (no worries!)

Same process with the Rustolium except I eliminated the 5mm/second row since that was overkill. I also stopped midway through the top row since it was already too weak.

Now I removed the paint on both tiles. Acetone for the Rustolium and a soak in a tub of water and a scrubber sponge for the home-brew.
The powder near the edges of the squares gets heated and can get stubborn, don't be afraid to scrape it with a razor blade or use more aggressive scrubbing.

One thing to notice after the cleaning is some former dark squares are completely gone. This is due to the TiO2 turning black, but not fusion with the glaze. They literally flaked off.

Now for a closer look at the test squares
This is the home-brew mix.

The overcooked area (lower row, right side) can be seen. The area directly above looks good and the black is flush with the tile surface
The Rustolium has similar quality in the same power/speed area which means either method can probably use the same laser settings

You can see the black gets "grainer" with the greater power or speed.

A close up of the sweet spots:

Pretty much the 15mm/sec row and anywhere from 35% - 50% power. Not quite linear, but higher power at a higher speed or lower power at a slower speed relate. This is important since faster speeds (at higher powers) will get a project done quicker, but using lower power (slower speeds) will let your laser diode last longer.

This process can do more than just black/white, you can also do grayscale photos. The thing to keep in mind is that the TiO2 only reacts with the glaze at a relatively narrow power/speed range. Best results are using some form of dithering that tricks the eye into seeing various shades of gray (like a newspaper).

What's up next?

No Idea! I'll think on it or entertain any ideas you followers have in mind