Anyway, the tests were a partial success. Which means some of it failed.
On the 1050 high carbon steel,all fluxes, from the straight laundry borax to the hyper-flux with a half-dozen ingredients worked. The best results were from the fluxes that had some fluorite in them, and the worst was the borax/sal amoniac mix, though I'm willing to believe that that was just a coincidence and not a particular feature of that flux.
The stainless tests, on the other hand, were a failure. No sticking, not even a bit. Examining the pieces afterwards showed that both test pieces had a lot of black oxide on the inside, despite the fluxes and having been ground to a bright polish before the welding attempt.
Next step, then, since I believe this is possible, is to experement. The notes from others who have gotten this to work indicate that a more aggressive flux, by adding in a higher percentage of fluorite, may do the trick. In addition, I am going to put some charcoal in the gas forge to scavange oxygen, which should retard any oxide formation as well. If this doesn't do it, I'll try a third technique -- remove the oxide layer, minimally flux, then wrap in stainless foil, squirting in a bit of oil before crimping and sealing the foil around the billet. This will exclude oxygen, the flux will remove any oxides, and I should be able to get some stainless welding action going.
In other news, I finished the first welds on that large billet, and drew it out to about two feet. I'm now debating internally whether or not to draw it out further, or to instead do the first folds at this thickness. Either way, I won't get into the forge until Friday, when I hope to finish the folding and welding. My goal for this billet is about 360 layers, and I'll be doing a pool-and-eye pattern, so once I get the folding done, I'll be drilling a gazillion holes partly through the billet, then flattening it out so the layers form a nice set of patterns. I'm going for smaller holes than last time, and it makes a tighter pattern with more activity.
I should be able to get a good three or four wheels out of this billet, when they're doing I'm thinking seriously about making a single piece forged damascus chef's knife out of a twist pattern.