Thanks a lot guys !!!
As for the hair spray chipping technique,you spray the metal finish that you prefer(for me its alclad only)then you seal it with an acrylic clear varnish,let it set more than a week.
Then apply the hair spray only under the color that you are working at that time,not the whole model,you don't want the hair spray to set for a long time and hardens too much.
And before the color sets entirely,you hit it with a water moistened hard brush (it prefer toothbrush)and you keep hitting until it starts peeling of the paint,you stop when you have achieved the desired results(it better less than more)
In areas that you need more control of the effect such as (panellines,panels, etc)you moist the desired area and you lightly scratch with a toothpick !!!
hope its understandable ......
Sory for my poor english !!!