This red and black faux marble looks more like granite. The character of the rock is that of embedded crystals.
The ground for the marble /granite which is called red porphyry, is a dark reddish brown, mixed from vermilion red and black.
Then, with a tooth brush, flick or sprinkle the background, with a color formed of vermilion red and white to reduce the brilliance of the red. Don’t make this too runny sot that it spreads… each spot should be distinct.
Then you will sprinkle it again with still lighter colors… until you have the surface covered with freckles of reds, browns, pinks and whites.
You can also have a greyish background stone color, formed of white, black, and umber.
When this is dry, spread on a thin layer of clear glaze and, and sprinkle it with a suitable grey color. This process is repeated with the same color, containing more black and a little red, but the sprinkling is done more fully, that the colors may run into each other. A white, stained with red, (pink) is then used in the same manner.
This Baptismal font in the Cathedral of Magdeburg, Germany.
The font is made of rose porphyry from a site near Assuan, Egypt.
Originally designed as a fountain with a hole in the center, the item may be thousands of years old, and is still used for baptism today.