I have taken all my varnish back tot he wood and noticed one or two black sections and some not so black sections. Whats the panels view on the best way to treat this ?
You did not say wether the staining was from water damage or not. Assuming its not from water, you could try bleaching the wood with Oxalic acid. This will remove all the colour ,so you would have to restain to match surrounding area. This works on most stains I have not tried it on water damage,it may work. More experienced fourmites will no doubt answer that.
Re Oxalic acid.
Buy it from a chemist
Mix as much powder as you can into hot water (super saturated solution)
Paint on to the black areas
Cover with cling film to reduce dryimg and keep the mixture working for longer
Re-apply
Rinse with clean water
allow to dry
sand and coat
If that does not work, and the staining is deeper, say from and iron fastening, then it becomes an 'Honourable Scar Of Time'!
Live with it, enjoy it!