I'm interested in welding up a damascus billet of some nickel sheet I have (.06 inch thick) with mild steel. I've read that because the nickel won't weld to itself you need to add an extra layer of steel every time you make a fold. How thin can/should that layer be? Can you use shim stock?

Also, have people done this with coke/coal or does it need to be charcoal (I only have a solid fuel forge).

Upfront let me say I have never welded nickel and mild steel..I have welded a lot of nickel and high carbon steel. I always weld the nickel mix in a can. Too lengthy for me to type it in here. 

We covered it in the knife making lessons, advanced sessions,,,For sure not a beginning forging chore. 

One thing to consider is wot is the mild steel you have? 1018 is harder to weld for most folks than HC,,1036 is said to be harder to forge weld than that.

When I do a high Carbon billet with pure nickel layers it is for a knife. I have to keep track of the percentage of nickle in the finished product so I still have a blade that will  take and hold an edge. 

Mild steel takes more heat than HC to forge weld....

When I weld a billet with nickle and HC, and cut and restack for higher layer count I will sometimes add a piece of HC in between Layers like you asked about, Almost always it is under 050" thick.

Thank you for the reply! I'll be mostly using gokunantetsu - an ultra low-carbon steel they have here in Japan, and then I was thinking of using 1008/1010 shim stock as my filler. If I can the the process down, I would like to use it on some antique wrought iron I have here - but not until I'm at least fairly confident I can do it without ruining the stuff!

Also, for the weld, is it ok to take the mild steel/nickel up to a full sparking heat if I don't care about carbon content?

I have welded pure nickel and damascus  shotgun barrels (cut and flattened out) the shot gun barrels are nearly pure iron  (or spark that way.

 welding was not hard but from memory I did it hot by my standards but way below sparking.

Thanks, basher.  What kind of fuel were you using?

this was welded in a gas forge with borax.

 nickel was 0.4mm stock.