steven,
they are more than likely aluminium, which if you are blading will tend to leave a trace of a powdery like substance on the window when you have finished.
like i say if you are blading then we have found the best way is to try not to do too much detailing as this is usually where the powder comes from ( off the scrim).
if you are wfp then i would do all round the frames first then the window let them drip down until the dripping stops then very,very carefully rinse as close to the top of the glass as possible without the water touching the frame.
youre not the first one to have probs with these they can be a pain