My project in Cement Tile Design and Production for Beginners course

I made these two tiles using a simple 3D printed mold. In the first one I saw many cracks on the surface, after leaving it into the water they tend to be less visible. For the second one I experimented more with the grey-purple color, calculated the pigments better, used more material for the colored part, but still got some cracking, and also confused a bit the color placement, so it is not symetrical as the first one. Can you suggest some tachniques to avoid the cracking? Am I pressing too much the filler material?

Thanks Juan for your advices.
I will write here my learning while building these tiles, maybe it is helpful for others as well:
- The colored material needs to have more water, it has to pour nicely. Also I shaked the container I prepared them in so I would't have air bubbles as my second tile had.
- I have a 3D Printed mould which helps a lot because it stays flat on the glass.

As materials go, for this tile model I used these quantities:

1. For the colors I prepare 400 grams of white cement with 100 grams of sand and divide them like this
- for the white: 140 grams of material, nocolor
- for the violet-grey: 140 grams of material + 1.5 grams of blue pigment + 1 g of red + 0.3 g of black
- for the yellow: 220 grams of material + 11 grams of yellow pigment
2. For the dry material between the layers: 90 grams of sand + 90 grams of cement
3. For the filling material: 700 grams of sand + 235 grams of cement