Wish I knew of some miracle one-step treatment.
What I do is effective for both oiled and varnished oak windows & doors but quite protracted.
1. Good all-over scrape (usually with hot air assist) followed by sanding;
2. Thorough wipe with methylated spirits (using fine wire wool). Weathered bits go very black initially then quickly dry to a silvery-grey.
3. With appropriate size brush, paint those silvery parts with heavily diluted (1:4 or 5) wood whitener/bleach; more natural colour almost instantly comes through.
4. Immediately wipe all over the area with damp cloth, several times, regualrly cleaning damp cloth.
5. Let it dry thoroughly for an hour or so.
6. If there are still blackish areas, repeat the whole process.
7. If there are over lightened areas, paint/wipe these with heavily diluted suitable oak (water-based) wood stain.
8. Keep repeating this process (with either meths/lightener or woodstain) until you are staisfied with the effect over the whole dried surface.
9. Lightly re-sand and then apply whatever final treatment you want.
GJG - Cotswolds, England, August 2008
