Mike's barrels demonstrate that with most doubles with a top rib extension (esp. if the top rib contributes to a bolt lock-up) the extension is a separate segment. AND the challenges of coloring steel.

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The extension was usually indexed in some manner with a screw

L.C. Smith which was brazed

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Parker GH with poorly matched D4. On refinishing the higher carbon screw stained much more darkly

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Some extensions on damascus barrels were a non-twisted (layered) laminate, others solid steel; Parker Lifter Bernard barrel with steel extension which stained more darkly

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The iron component of pattern welded rods was no doubt wrought iron. The steel was either Bessemer/Decarbonized (carbon .06 - .1%) or 1002 - 1005 low carbon low alloy steel.
I've done composition analysis on ONE segment of rib, a c. 1912 Lefever Arms Co. DS, and it was AISI 1011.

So coloring different composition steel was and is real challenge. Hopefully Mike will post the final results.

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