A while back, don't know where, but I saw acool picture of a german tank and on teh turret it had the rusty impression, whith rust streaks, of where the spare track used to be. It was a very neat and realistic effect. Any idea how to do it or if someone else saw this model?

Godfather

What my guess would be Is take some sparetracks and make a rust colored wash. Dip the sparetracks in it and push this onto your model.
as soon as the wash touches your model it starts to run down creating the rust streaks and when you get the tracks off there will be an impression of where the tracks have touched the turret in rust color.

Beware that I have never used this method but in some way this seemed a logic and simple approach to this

Sounds logicall to me as well faust ...... and i suppose to get the marks in the right places you will need to place the tracks. Another suggestion for these streaks is to put a little dot of rust-coloured pastels at the start point of the streak and then with a brush dampened by alcohol pullt his down. It will run slightly and fade as it comes down. Practice on a scrap first so you dont ruin your paintwork.. and to get the technique right!

Try making your own "Rustall". This is a bit involved, but it results in real rust.

Take some 0000 steel wool and put it in a wide mouthed jar. Cover with water and place in a sunny window. AS the water evaporates, keep topping up the jar. Eventually, the steel wool will have rusted away and you will be left with a brown sludge at the bottom of the jar. Carfully pour off the left over water, and scrape out the sludge onto some tin foil. Let this dry. You can now grind up the result into a very fine powder. Mix with some turpentine or paint thinner and you can apply this to your model. The thinner will evaporate and the rust particles will stick to the paint.

As I said, it takes some time to prepare, but the results are worth it because you are using real rust.