Iron Silver?

[PedroTheSlayer]

What is that and how to make bars from it?

[SlapHappy]

you probably mean iron sliver (sliver means a small piece) you get slivers from melting down armors or weapons that goblins and skeletons wear (since their game mechanic was changed into worn equipment)

you can always make bars from eighter ore from mining or metal slivers from melting down worn equipment

[D3s_ToD3s]

There is a second "bars" choice in the forge-menu
There you can choose (or just kleave "all") wich kind of bars you would like to have.
The smelting gnome will then start hauling 10 slivers of one type togheter and one coal and will melt those into a bar.
Thats a easy way to stock iron and steel on later years.