I grabbed a few minutes today (spread out a bit) to have a crack at another experiment which I'll need for the bridge I'm planning for ExpoNG. I'm reasonably happy with adding rust as a detail to a model but I've never tried to paint an entire item completely rusty. There are plenty of rust coloured paints and washes available but the problem is you need texture as well as colour variation as a well rusted surface tends to be pitted. On the bridge I'm modelling there is quite a lot of rusty girders and flat-bottomed rail so I needed to experiment a little.
What you are looking at here is a piece of girder at the back (which is just 3.2mm tall) and a piece of code 60 rail at the front. Both have been treated in the same way. To get the pitted effect I first sprayed on a layer of red oxide primer before gently sprinkling on some light weight hydrocal casting powder (it was the finest stuff I had to hand that didn't want to clump) to the wet paint. I then knocked off most of the powder, allowed the paint to dry for a second or so and then sprayed a second layer of primer. This seems to give a really nice texture although I might have added a bit too much powder to the rail sides. Once this was all dry I liberally dabbed on some MIG Productions Standard Rust Effects which provided some nice variation in colouring and shading. I then dry-brushed on a small amount of RailMatch Light Rust (#2404), before some final dabs of a rust wash from Flory Models.
The photo is very unforgiving and from a normal viewing distance the texture is less pronounced and I'm fairly happy with how they look.