I drew into the polystyrene with a pencil, indenting the surface and made some linear wave shapes. Using acrylic indigo paint mixed with a little screen print medium to give a longer working time and thin out the pigment whilst keeping a sticky consistency I inked up for another trial print. This is on the top left.
Hmmmmmm.... I thought this is looking interesting so I cut another piece of tile and rather than drawing across the surface I just pushed the pencil into it. It was good fun in a bubblewrap kind of popping way until I got a little impatient and started getting heavier handed and kind of carved into the tile. If you try this at home BE WARNED have the hoover on hand to catch all the little bits of polystyrene that will fly everywhere, don't wear clothes that may have a tendency to have static and it would be good to have someone else in the house in case the door needs answering. (I speak from experience - I had followed none of the above and I got a very strange look from the postman answering the door with polystyrene flakes stuck all over my clothes and in my hair looking like Frosty the snowman with a very sheepish grin - I saw his shoulders shaking as he walked down the road laughing. I can't say I blame him I was a bit of a mess.)
And here is the result after the embarrassing encounter with the postman.....
It might not look much now but I am planning on working back into it once it's dried.