Good preparations will enable successful end-results. Start by washing, scraping, sanding, priming and applying putty before getting started. In this way, your windows will last longer without having to re-do the job too soon.
SEAL ANY LEAKS. To be able to paint properly, the wood must be dry, and the glass and putty must be intact. Otherwise, the window will be destroyed by moisture entering the wood. If you need to apply new or supplementary putty, start by lifting off the window frames. Remove any remaining sealing strips, and clean with paint cleanser. Pick away any loose putty. Press carefully with a knife between the putty and the wood – never towards the glass! Prime the window frame with oil and paint. Wait until the primer has dried before starting to apply the putty with a putty knife.
DO NOT USE A HEAT GUN! Do not use a heat gun to loosen old paint. There is considerable risk that the glass pane will crack. Instead, you can heat with an IR lamp that can be rented from your paint store.
TAKE CARE OF MOUNTINGS AND FITTINGS. Unscrew the window's mountings and fittings. Apply Vaseline to the connection fittings between double windows so as to protect from paint daubs.
SCRAPE THE FRAME. If the frame has been painted several times, start by scraping seams and joints so that the paint does not become too thick and prevent the window from being closed.
PRIME THOROUGHLY. It is very important that the windows be thoroughly primed, including the outside, with penetrating priming oil under the first coat of paint. Sand everything that is to be painted. Weather-greyed wood must be sanded down to healthy wood. Then prime oil all clean wood surfaces, including putty seams. Ensure that all leg-ends be impregnated with oil. Allow the priming oil to draw for 30-60 minutes before painting with primer.