Hi Craig,
Thanks for your suggestions / ideas, they really are much appreciated.
If you were to rerun the program several times does it etch into the tile deeper?
I don't know, possibly it would - but the secret is not to completely destroy the surface glaze, just to heat it, creating the micro fractures / melt which capture the carbon soot (if that's what it actually is).
Also wondered about applying rub-n-buff for an added effect. You could mask and color areas for effect.
I have tried rub'n'buff after etching and yes colours could be produced but rub'n'buff is easily removed with many different household solvents and the finished tile, although looking good would perhaps not be so durable (I doubt it would survive too many dishwasher cycles).
Others are currently experimenting with coloured enamelling powders and laser fusing these onto / into the tile surface (similar to my toner experiments shown earlier). So far, the results are not that spectacular but I think the idea has great promise and definitely needs further investigation.
Tweakie.