Once oxidised they stay forever oxidised.
You can certainly clean them to the point where the water appears to run clear, but if done as described, you should still go back to the window a few minutes later and carefully just do the glass very lightly, although even then you may still get spotting.
The following month, quickly and just barely go over the frames, scrub them or wet them too much and you will remove faint amounts of oxidisation.
Concentrate on the glass and you should be ok.
As you gain experience you can get the hang of getting windows with oxidised frames up to an acceptable level.
I also completely agree with Squeaky's post (and I think that's the first time I've ever felt compelled to confess to such
) WFP is not an all singing, all dancing answer to window cleaning, and there really are some windows, which for some unfathomable reason will not come out right no matter how many times you wash them using WFP.
I had a garage showroom a couple of years back; two identical, large showroom windows that were side by side; one would come up perfect every single time, and with the other pane, even though I persevered once a fortnight for several years, every single time I had to go back outside and re-clean with trad methods.
Now here is a little known fact for you all with regards to the reasons behind the oxidisation of UPVCframes!
It is the chalk that manufactures use in them............
No, really, a customer of mine used to sell double glazing and informed me that at the cheaper end of the scale, rather than use more expensive chemicals/compounds etc, in order to enhance the colour/whiteness of the UPVC they actually add chalk in the manufacturing process.
Anglian and Everest have the lowest values of chalk content in the makeup of their UPVC and as a result will resist degradation due to oxidisation from ultraviolet light for donkeys years.
If you wash a UPVC frame and the water turns into skimmed milk then those frames are right at the bottom of the pile with regards quality.
Everest and Anglian are not the only ones to use top quality UPVC though - but they are the most expensive - so should you be contemplating some new windows yourself, ask the salesman for the tech specifications of the frames...the higher the % of chalk then the lower the grade of UPVC.
Ian
