This is a very old and I think nowadays almost unknown modelling technique : making cobblestone streets from eggshells.
First of all a size comparison. The 10 cm wide street that I mentioned days ago looks more or less correct with miniatures from 28 to 54 mm size. Its a full road for the small guys, a good one for 40 mm soldiers and still wide enough for the big ones.
And it has to be enough because nothing really suits 54 mm miniatures, most of the time it is impossible to support them with things that fit to their scale. A castle for example that is in the 54 mm scale would use up half of the room I am sitting in now.
Making the eggshell streets
The process is easy. First : Eat the eggs. No, I am kidding, simply collect eggshells for a while. Peel off the membrane and keep only the shell itself.
Apply glue on the surface of your road, put a piece of eggshell on the glue and press it down so that it breaks into small pieces. Arrange the pieces with a pointed tool.
The whole process goes faster than one may think. For example, cutting carton into pieces and gluing them to the board would have cost more time and would mean a lot more work. And it would never look that random. (if wanted)
Yes, I could have bought ready made cobblestone foil or something. But that would make me depend on them. I can make or repair eggshell streets as much or often I want (... and as long as I eat eggs). And I can make small ways or places with it and use the same stuff wherever I want.
At the end of the day I paved four street pieces and started a fifth. But I am running out of eggshells now. Hmmm, what are we going to eat today?