I tried this on the computer, it didn’t look as though it would be an improvement. I’ll try anyway, just got to go and buy some more red tiles.
Edit: Turns out the tiles are a little special, red is actually tomato, green: pistachio, orange: pumpkin etc.
I’ll try, logically it should work.
If the tile was covered with tape entirely … couldn’t you then just paint where the laser had burned thru the tape. Just a lite misting of spray paint to highlight the etching.
OK, seems like a plan, I’ll try something along those lines. It may be more efficient to cut a shape through the tape first, remove it, then engrave the image before spraying. Good for simple images. I’ll try both methods. 
That would work - there are other clear finishes that would seal the ceramic as well I would imagine - esp. if kitchen backsplash - not like a shower wall, doesn’t get too much direct water exposure. (I would think)
Continuing with the experiments:
Santa now reversed, unfortunately I forgot to reduce the DPI or dither the image, these are the things you learn… next time.
More whippets, putting masking tape on the tile made no appreciable difference to the depth of cut and would make it easier to paint or seal the engraved area. Engraving the image with 90° rotation does add to the image, When I engraved the first image, above, I neglected to refocus the beam after cutting the tiles, not so this time but I think it was better out of focus.
Engraved on very cheap hardwood ply, seems to char a lot compared to the MDF
Ready to seal/paint, I don’t think I’ll bother trying to remove tape before engraving given it doesn’t seem to make much difference to the image.
This is a vector cut rather than a raster engrave.
I’d definitely seal it–I’d seal the whole thing to keep the grout clean anyway, and the etching would just go along for the ride.
I like the smoke on there, it kinda helps the imagination fill in the blanks. Fleshes it out as it were.
I wonder if firing a layer of clear glaze on the tile would diminish the visibility of the laser engraving? If not, it would be one way to make custom waterproof shower tiles.
Thinking further, a thin layer of underglaze could be added before removing the tape, then clear glaze on the whole thing after removing the tape. That would certainly give a striking result after firing.
Curious, when you get the tile wet, how does it affect the image? I have some black river rocks I etched hoping to use them in the sink…but when they get wet, the writing disappears…it comes back when they dry though…
That characteristic is inherent due to the way light reflects off the surface texture. The laser leaves a sharply pronounced difference in texture - until it’s wet, and the moisture film reflects uniformly.
In cutting stones for jewelry, you progress through different grits to achieve a polish. Scratches from 100 grit completely obscure the character of the stone, and wetting it allows a glimpse beneath the texture.
To maintain visibility on your black rocks when wet you will have to treat the etching with a pigment, or perhaps lacquer the stones to keep the etch dry…
Although that will have a similar effect to a degree.
That’s a feature! It’s like disappearing ink!
I had the same thought, incorporating the vanishing and reappearing in the design.
There is a design for that application out there somewhere… I can feel it.
Now that I think about it, there are physical textures that are hydrophobic, you can’t wet them. I doubt we could achieve that level of surface accuracy with our lasers, bit I don’t know.
How about this hydrophobic spray http://www.homedepot.com/p/Rust-Oleum-NeverWet-18-oz-NeverWet-Multi-Purpose-Spray-Kit-274232/204216476 (dries frosted) or this one http://www.homedepot.com/p/RAIN-GUARD-16-oz-Hydro-Lok-Liquid-Repelling-Treatment-TPC-1000/205826692?cm_mmc=Shopping|THD|G|0|G-BASE-PLA-D24-Paint|&gclid=CjwKEAiAsMXBBRD71KWOh6fcjRwSJAC5CNE18SdGYVcLE08PPxXvYWEwtMa8EwKNw8wVcXnqiaklwBoC3Ifw_wcB&gclsrc=aw.ds (dries clear)?
Mask the stone or tile, do the engrave and then spray it before removing the tape mask. Once the coating dries, remove the tape and it should repel water only from the engraved spot.
I think I’ll grab some sprays & some slate (that really grabs water and lasers well so should be an excellent test case) next time I’m at the big box store.
I’ve been playing some more.
I now have a whippet engraved into acrylic, rocks, rusty steel, and leather. Not so much “into” the steel and rocks, more “marked on”.
Have yet to try bacon.
I tested the engraved tiles under water, leaving them for a couple of hours to make sure the water “got in” to the engraving. Only the red tiles showed a loss of clarity, I suspect this was because of the density of the Santa engrave. Forgot to take photos, I can repeat the test if folks want to see.
A blue or deep red ink/die on the etch would really make that stand out.
Wonderful to actually see the test etching on dense material.
Thank you for the image! Interesting.
