Darken Friulmodel tracks with Goldsmiths liquid.

For cleaning I used vinegar and left them for 30' and after scrubbed them with a toothbrush.

 

Then I dissolve the liquid into water in 1:3. I place the tracks vertically (photo below) for 7'and then rubbing them with toothbrush (between the treads and the grooves).

Thereafter, clean with tap water and rub the tracks again (because this fluid is not already dilute such as those of  trade and leave a yellow precipitate to the tracks).

Dried now and ready for dusting and roughcasted according to your tastes.

I used the liquid that Goldsmiths use for darken their metals.