I d start with a very good cleaning as recommended above.
Cleaning black marble clock.
Remove old oil from the gears with the brush and use clock oil to re lubricate.
If you follow the instructions carefully you will be amazed at the result.
There may be some recoverable gilding beneath the grime so leave these lines alone.
Polish the pivots with a dry cloth.
Marble can be polished with abrasives to make it shine slate needs some coating like shellac or paint to make it shiny.
There are various cleaning polishing materials available the most well known i think would be marblack and is available from the big clock material suppliers.
Keep cleaning the clock until you are sure you have removed all grime old polish etc.
Now it is back to its former glory.
Apart from the marble how can i restore the brass decoration.
I want to clean my clock as below and get wax.
240 then 400 and finish with 600.
Follow with a dry cloth to dry the floors and avoid streaking or water spots.
Clean the grime between the pivot and the hole of the plate on the movement with the brush.
Despite this clock s lamentable history and its present appearance i knew this had been a quality clock and i wanted to restore the case and movement if possible.
Apparently this was the second.
I m not sure it is really tarnish or it got painted with black because i can strip out with knife.
Both of these clocks appear to be of rare black belgian marble not slate.
The tarnish is toooo thick to get through with paste polish i m using peek.
Clean the clock case thoroughly especially any areas of inlaid marble.
Black marble t he photographs in figures 1 and 2 show what remained of a clock which was described by a dealer friend of mine as just what i was looking for.
This lovely black marble holy water font was broken and in a bad state when i found it.
French black marble clocks are still very underrated by clock collectors and the general public alike hence they are relatively cheap clocks to buy and can be prone as here to abuse or neglect.
Take the mechanism out because you will need to use water.
Dismantle the movement and clean it using the clock cleaning solution and a small bristle brush.
I have used it on very dirty dull grey cases and restored them to a sparkling black finish.
Both are inlaid with a semi precious stone called porphery it s not painted graining.
To clean black marble floors dip a mop into your choice of cleaning solution wring out the excess water then clean the floor as you normally would.
For bathtub tile and countertop backsplashes spray the surface with solution then wipe with a clean dry cloth.
If your clock is very badly scratched you can start by using very fine wet and dry emery paper.
Well there was some truth in that as i am always on the look out for clocks to restore and this clock certainly would benefit from some restoration.