Louis,
I use acryllic artist paints for this.
Use the Burnt Sienna with a lot of water and with small soft brush put it down on the ballast.
But before brushing the rust color, I paint the balast in an aged color (an equal mixture of Ultramarine Blue and Burnt Sienna and a lot of water). Paint all the ballast with this and when it is dry, paint at random places more with this color.
After drying paint the rust.
Paul
I use acryllic artist paints for this.
Use the Burnt Sienna with a lot of water and with small soft brush put it down on the ballast.
But before brushing the rust color, I paint the balast in an aged color (an equal mixture of Ultramarine Blue and Burnt Sienna and a lot of water). Paint all the ballast with this and when it is dry, paint at random places more with this color.
After drying paint the rust.
Paul