I varnished some board black and subsequently added two or three layers of uncoloured high gloss paint.
Afterwards I cut "tiles" with the size of 2 cm x 1cm and fixed them with tacky glue to uncoated paper.
I added some trim made of corrugated board.
And this is the first finished wall...
I will grout the tiles after adding some more layers of uncoloured high gloss paint with emulsion paint.