Just a quick update. The clock originally looked like this after cleaning off the years of accumulated grime:
After a fair bit of trial and error I used the following:
3 coats Liberon Ebony Spirit Woodstain,
2 coats Slate Oil,
1 coat Renaissance micro-crystalline wax (thanks for the tip CB),
2 coats Painters Touch Acrylic Gold paint (from Homebase) to detail, put on liberally with brush & scraped back with razor blade between coats.
a final 2 coats Renaissance micro-crystalline wax.
and this is what it look like now:
My initial trials with oil worked well at first but the pale patchy areas came back to haunt me after a couple of days. Tried Priorys Black Slate Renovator without success. The spirit woodstain has worked well, its not perfect but acceptable. Some surface corrosion is noticeable at certain light angles & as Oldhippy rightly states the only way to get rid of this would be to pull it apart, grind & polish. The pale patchy areas are now well masked. The Slate Oil appears to be none other than boiled linseed oil & was slower to dry than the original Floor Oil, If I did one again I would use Floor Oil.