Paint with 1 x coat of microporous paint ,making sure to paint all the sealant putty but to not leave more than half a milimetre of paint on the glass inside and out.Dont be afraid to add some more white spirits to the paint to stop it from being too toffee.
Paint with a microporous top coat.This time painting over the glass inside and out.
Paint with a microporous top coat again painting over the glass and the sashes and on the frames the last coat is more of a touch up / patch coat.
Take off the paint you put on the glass using a Stanley Scrap.Water and Fairy liquid can help to lubricate the glass.When it becomes too hard to take off simply change the blade.This also cleans the windows at the same time.
I recommend getting
A large sealant gun
2 litres of white spirits
1 x 2.5 litre of Johnstone microporous undercoat/primer
1 x 2.5 litre of Johnstone microporous topcoat/gloss