I saw a placemat in a market which was made of a leather imitation. This looks a lot like a cobblestone pavement.

The placemat was already a very light gray, and I left with a mixture of water, a drop of washing-up liquid and a few drowning black paint. Simply "smear" over a large area with a large brush. That then digs nicely into the small joints.

I then wiped the still wet paint off with a sponge.

When the paint had set, so it was so slightly sticky, I aged the whole thing with a little black and brown patina powder.

Ready