TIG - halo of contaminant?

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I did a bunch of TIG yesterday. I welded together some big steel beams for a gate post. One was galv, one was painted. I ground them both clean to bare metal with a flap disc a good 3/4" from the weld. Still, I picked up some weird contaminant on the tungsten. It was like a little paper thin halo or disc of hard stuff about 1/16" from the tip. About 3/16" total diameter. I never dipped. The tungsten was freshly ground. I couldn't pull the contaminant off with gloves - it was hard and stuck in place but uniform all the way around. It occurred right at the start of the day - I did my first run and noticed a tiny bit of contaminant in the puddle and then after that run noticed the disc on the tungsten.Pertinent facts:- 3/32" 2% lanthanated- 3/32" ER70S-6- 140A full pedal- no pulse or anything- argon at ~7LPM (~15CFH?)I ground clean the day before and it was fitted up and part welded, so in the morning I didn't bother going over again because of the join (a 6" x 3" beam joined to a 3" x 3" beam to make a 9" x 3" beam so the join was in the corner where the two corner radii of the beams meet). It's possible there was overnight flash rust, I didn't look closely. There may have also been overnight dust or whatever. There may have been grinding dust from grinding nearby. I should have wiped it down or at least wire brushed but I didn't, just got straight into it. Nothing immediately concerning anyway and the puddles were mostly very clean except a few tiny specks once or twice.The funny thing was the disc didn't affect the arc in any way at all. I would have expected crazy things - arc shooting off at weird angles. But it welded fine and the disc wasn't affected by the arc and didn't affect the arc. I'm just curious what it might have been?
Reply:I have heard references to this being a beard.  Could be the lanthanum leaching to the surface. I know I have to burn of the lanthanum before the tip glazes over when welding alum on AC.Weld like a "WELDOR", not a wel-"DERR" MillerDynasty700DX,Dynasty350DX4ea,Dynasty200DX,Li  ncolnSW200-2ea.,MillerMatic350P,MillerMatic200w/spoolgun,MKCobraMig260,Lincoln SP-170T,PlasmaCam/Hypertherm1250,HFProTig2ea,MigMax1ea.
Reply:Thanks shovelon. "Beard" pointed me to this thread and that's exactly what I experienced.