I used to heat my mk2 golf bumpers back in the day and that did the job

I have just used sun-pat peanut butter (smooth) - £1 at Tesco - and rubbed it into the trim at the bottom of the windscreen (not the one on the bonnet) which was greyish/white and it has come up deep black, better than any 'back to black' product I have bought over the years ( at 4-5 times the price ) . Also used it on my 'a' and 'd' columns and wing mirrors. Seems to work Ok, but only been on for a week so far . Can't go wrong for the price, as long as the local cats don't start trying to lick my car !!! Steve

Main car : FFRR L405 Vogue SDV8
Other car : Vauxhall Lotus Carlton
Past cars : FFRR L322 Vogue TD6 SE (Sept 2006 MY07) ; LandCruiser SWB ; 4-Runner ; Supras; XJS V12 LeMans