I have seen this technique wher you paint teh model black then teh base coat what would you pre paint amodel if using a light coloru dark yellow for example. Do you still need to prime if using this technique?

I just finished a Tamiya M3 Grant and used this technique. I did not use a primer but insead the made the basecoat the primer.

For the basecoatI painted the body a combination of 60% dark yellow + 20% black + 20% khaki. After I let this dry, I set my AB on a fine spay and mixed up some tamiya dark yellow and sprayed it in the middle of all the panels, allowing the darker base color show through on the edges. I will take some pictures and send them to you. Good luck and I hope this helps.

If you are going to paint your model a dark color, like dark green or olive drab, it's best to use a flat black preshading coat. Does not need to be a primer, I have used Tamiya XF-1 Flat Black and never had any problems. But if the model is going to be a lighter color, like Dark Yellow, Sand etc., Dark Brown would probably be better (black would look too stark).
Have not tried that myself (yet) but I heard it gives good results. And on Panzers you could use Panzer Gray or Red Brown as a preshading coat.

Having recently acquired an air-brush I have used this method as well and I am ver happy with it. I have seen build/painting reviews where guys have used a primer and still spray black as a pre-shading. I personally have not bothered with a primer before and never had any problems with it. As the other guys have said, dark brown or a darker shade of your base paint works well as a primer/base coat/preshading. You can even take it a step further and user a lighter base coat and spray in the middle of bigger panels to show more faded colouring. Dont worry about contasting colours as this can be taken care of when weathering and using filters!

Priming is not nececery, but I alway's do it. I use a grey auto-primer so that any flaws or errors are visuble.

I have not used PE before, but I was told that if you use PE it is better to prime so that the model and PE is uniform and the paint has something to grip to.

Just my 2 eurocents

#:-)

I use the darker base coat idea and "panel out" the model with a lighter faded color of the same base.A filter is,according to my experience,is a misting of the lightened base over the whole model,from a distance.This will help soften the contrasts between the dark and lightened edges.I have used this technique to great results.

I just recently stared using that method. i.e. Painting the primer color a Flat Black. BUT will agree that when painting a Panzer model. Using a Brown color as the Primer is the best
one to go with. I used to paint the primer using the grey primer. But I like the looks that a flat black gives off. Just my thoughts on the issue.

DAGGER-1

A filter can also be applied as a wash, i.e. you make a very thin wash of the color you want (lighter shade of the base, weathering color or even a darker color) and then brush it over the model (the whole model). A filter wash will blend the colors used, especially when you have a multicolored camouflage with high contrast (e.g. a sand color and a dark brown). This technique is used by Miguel "Mig" Jimenez. Looks great! Have not had the opportunity to use it yet, but I certainly will! :-)