Guys,
Folding and rewelding W.I. to get a more refined material does not make the W.I. become mild steel. Neither does it make a significant reduction in the percentage of slag in the W.I. What it does do is make the slag strings so very fine, thin and numerous that they are difficult to see without acid etching and magnification. This is what Mark is talking about 3rd run, A.K.A. treble fine, A.K.A. triple refined, it is what we always look for but rarely find. Mark, I can help you if you have any excess!! If you look for old wagon wheel, get ahold of the wheel hub bands (not the tires), they tend to be abut 1/8 thick, 3 wide, 20 long (unrolled that is) and great for a buttplate. For my W.I. triggerguards the raw material in old blacksmith tong handles is about right to start with. Flattening out a wagon wheel tire sounds like a lot of work.
Personally, I like to see some slag stings in the metal to show that "that ain't store-bought!" So, leave it bright so nobody would mistake the buttplate and triggerguard for a catalog item that everyone else uses. If folks don't see the slag strings, then educate them. Have fun on the project and fire up the forge. Show us the photos, too.
Jim