John,
I think you are using way too much power and completely destroying the glaze… leaving the raw ceramic exposed below. I have the same Neje A40640 laser as you and it does not give nearly the good result as my little Banggood 2.3W laser…
It looks as though you’re stopping at about 40% power on your test matrix. Start your test from 10% and I think you’ll start seeing the “blacks” you’re looking for.
For reference, my 2.3W laser gives the “best black” at about 1500-1750 mm/min and 100% power…
Since the Neje A40640 (~10W) laser is roughly 4X-5X the power of my 2.3W laser… possibly you should start seeing decent blacks around 1500-2000 mm/min and 20-25% power? As Ron said, you’re trying to melt and mix the glaze and TiO2… not blow it away. Also, don’t use air-assist, if you have it… though I keep a small personal fan gently blowing across the worksurface, just to blow the smoke away and keep the lens from fouling.
My $0.02.
– David