I don't know if this is a new method for chipping. What I have done for my 1/48 B-17G is spray it all chrome (I got this spray can at ACE Hardware in Houston Texas). I spray the plane's outer parts. After a drying period, I then spray the outer parts with the olive green. When the topcoat dries, I can fleck pieces out with a pick or a razor, but what I have done to get a larger and irregular chrome flecking is use a strip of masking tape, blue, or the common cream color tape. I stick it to the part and pull the tape off then it removes the top layer of green revealing the chrome.
Like I stated before I do not know if this is a new trick or has been used over a period of time. I thought I would share this "trick".
Gary G.