We had silver paint at IBM 50 years ago. There is nothing new there. I would question how much current it will carry tho. We only used it to repair CCROS cards. (Printed circuits on a paper IBM card used as ROM) It was milliamps if not micro amps.
I doubt this will ever be a practical way to run line voltage and low voltage would require a lot of current.
'Marmite' is a brand of ..er.. sandwich spread [?], made from hydrolysed yeast- a by product of brewing beer. Very high vitamin B content. Powerful stuff, very salty and an aquired British taste, although half the pop. can't stand it! Also sold in New Zealand and OZ as a slightly different formula.