Hi guys many thanks for the feedback and comments.
For umustb - the rusty look at the exhaust. To achieve that kind of look I mixed Vallejo various kind of brown color; like flat brown, orange brown, sand brown and a little of black. Applied them layer after layer until you want that kind of look.
For Jeremy, the following is my sequence of steps:
(1) With all the construction completed, the model was given a coat of primer proir the painting.
(2) Various kind of sand colors were mixed and airbrushed over the entire model.
(3) Russain green with a touch of black was airbrushed to form a camo pattern.
(4) By now the model look horrible and unpleasant prior the weathering.
(5) Next it is time to apply the filtering effects. Working in a small sections at a time using brush, I apply tiny dots of various acrylic paint in a random pattern, colors like brown, sand yellow, green, dark gray, black and etc. When dry these filters effect add a new world of subtle colors to the base color.
(6) Follow next, I applied spot oil washes to the model, not too heavy in the beginning, applied layer after layer until the point you think is enough.
(7) Chipping effect, I used brush and sponge technique, with colors like German gray, brown, sand and etc, dabbing to the area that most probadly chipped off by the crews or enviroments.
(8) By now the various color that applied onto the model may look a little contrasting, so I applied another light wash to tone down the look.
This T-55 tank is a fascinating piece of armour history and it gave an opportunity to apply all the latest painting and weathering techniques.
Thank you