I always look at those base stamps and think they are a great idea for creating diverse bases easily. So I decided to create my own.
I'm pretty happy with the result. No way near as good as the commercial ones but it works well enough.
First I started with some terrcotta coloured airdrying clay and made a cobblestone street section. I made the bricks individually then glued them to a sheet of MDF
I stretched some Instamold between two tiles I had left over from some work I had done on the house, Then pressed it down on top of the cobbles
After a few minutes I pulled it off and got some GS ready on a base
Then I pressed the instamold on top (after putting some vaseline on the top of the base.
The second one didn't have enough lubricant on it so I put some leftover bricks on there to paint up
Next I just have to paint them. If they turn out well then I'll do some more. Maybe add a few more details to the cobbles as well.