Two things people think of when they picture WW1 - mud and barbed wire. Mud is easy to make; here's my go at making barbed wire.
Basically, all I'm doing is painting some insect screen and then cutting it into strands.
This is just a patch I cut out of an old Screen Door I was dumping. It's plastic and the holes are tiny; small enough that a skinny, starving mosquito cannot squeeze through.
The paint is just a cheap can of Red Oxide. It really doesn't matter if dust and dirt sticks to the mesh; on the real battlefield, real barbed wire would have been covered in all sorts of muck.
These days barbed wire is galvanised, so it stays shiny for a long time; many years. But I think they had better things to do with Zinc in WW1, so I don't think it would have been galvanised; I think it would have been made from mild steel. In that case it would have rusted within hours.
I took the paint and mesh into the garage and gave it a generous spraying. The temperature has suddenly dropped here (it's -15oC) and that will affect the paint drying, but this doesn't have to be a perfect looking job; in fact the dirtier the better.
When I get a few minutes to myself, I will be cutting this up into strands. But today, the kids don't want to sleep so it will have to wait.