Did a fabulous workshop recently, incorporating Powertex into a painting. This was all done in five hours - pretty intense at times trying to keep up!
The base is a 18 inch by 15 inch box canvas.We used corrugated cardboard with the Powertex, and when that was dry, we painted over it with something that contained iron filings (can't remember what it was called but it had a rather strong odour!). To create the rust we then sprayed copper sulphate (I think). It started going rusty within minutes.
The bottom corner is random detritus - bits of wood, hemp, sand and dust.
In between all those steps, and whilst the layers were drying, we painted the farmyard scene with acrylic paint.
It is difficult to convey what it feels like looking at this, as it is quite large, it really does seem like I'm inside a rusty old barn looking out!