250EX very strange welding, was I given something other than pure argon??

[Gandalf]

Hello,

I have been welding with the 250EX for a year and half now, with flawless operation from the machine. My welding skills are progressing. I am mostly doing automotive projects, aluminum, with the occasional stainless. I never needed more than 120 amps up to this point.

I switched in a fresh bottle of argon today, flipped to AC, and tried to tack an aluminum throttle plate to a manifold. I got a weird discoloration, erratic arc, and no puddle. I grabbed a piece of 1/8" aluminum plate and tried to run a few lines to test things out. The arc was dancing around, making these strange tiny pits and circles, lots of black speckles and creamy-yellow discoloration beside the attempts at lines. I played with the amount of argon flow... it made no difference in the look of the outcome. The flow sounded and felt normal. The tungsten wasn't burning up, but looked black and shiny. Freq and pos/neg dials were about noon, also quite normal. TIG high freq start was fine. No pulse used. There is decent penetration.

This is what I am suddenly dealing with.... here's a pic:



I could be having a large brainfart (???) But I cannot figure it out. I really haven't needed to change much of anything recently besides flip the switch between AC and DC, and nudging the amps and the flow. And it's not how clean the aluminum is. This was set at about 80 amps, and a new tungsten.

Can the argon they gave me be something other than pure argon?

Any help much appreciated!
-Martin