Thickness of black layer in explosion Damascus?

[Leon Husock]

I'm hoping to make a bar something like this: 57055-2208367381de110a53cf87965a59cfd4.jpg

And I know that the way to start that billet out is by putting a very thick layer of black (i.e. non-nickel alloyed steel) on one side of the billet. My question is, to achieve something like this where the patterned element is almost framed by the black, how thick should that layer be relative to the section of alternating nickel/non-nickel layers? If my layered section is, say, 2" thick, should the thick black layer be 1/2"? 1"? The same thickness as the layered section?

 

[weo]

If you look at the final piece, you can see that it's a square made up of 4 smaller squares, and if you look at each piece individually you can see that it's probably a square bar about 1/2 black, and 1/2 patterned that's been forged on the diamond and re-squared.
I hope that makes as much sense to everyone else as it does me....

But, there's no real harm in having more black than needed, it'll just give more of a border/frame

 

[Leon Husock]

That was my best guess too. I wasn't sure if maybe in the process of everything getting smooshed and stretched it changed the proportions.

 

[weo]

That was my best guess too. I wasn't sure if maybe in the process of everything getting smooshed and stretched it changed the proportion

I guess this depends on how fast (and accurate) you are at forging.
We always have to keep in mind that there is steel loss each heat, so the fewer heats it takes you, the less you need to worry about the above proportion changes. Also, (as you are aware) you need clean/flat surfaces for forge welding things back together, so the more post-forging grinding that you need to do will also affect the proportions.

 

[DevinT]

Looks to me like the black is slightly bigger than the brighter area.

Hoss