Steve, I have done some forge work, and was taught forge welding both with and without using borax as a fluxing agent. I was told it was important to scrape off the flux or scale from the surfaces being welded just prior to joining to get the strongest joint. Of course, scale begins to re-form immediately so it would be next to impossible to make such a weld without at least a small amount of scale entrapment unless you could do it in an oxygen free atmosphere. Steel mills use both mechanical scale breakers and high pressure water sprays to blow scale off of slabs, blooms, or billets just prior to entering the rolling mill to minimize rolled in scale.
I've done a great deal of oxy-acetylene welding and learned early on to manipulate the flame and puddle to float slag, scale, etc. up and out of the weld joint, so I'm sure it's entirely possible to weld steel to steel or wrought iron to steel without use of flux. I was just curious how you minimize scale inclusions when welding Damascus. I'm also curious just how much this inclusion of scale affects the strength of the weld joint. It might be interesting to compare the force required to break weld joints of equal size and composition using a forge welded joint as compared to a flux or inert gas shielded welded joint. Pete's observation of barrelsmiths using a scraping device on the anvil makes sense, and hammering the red hot metal knocks a lot of the scale off the surfaces too. Obviously, these welds are sufficiently strong or a lot of us would have had our faces blown off. Knock on wood!
