Strange GTAW Aluminum Problem, Update

A few weeks ago I wrote of a problem while Tig welding Al.
The problem was, If I inadvertently tried to add the filler wire to
early, it would make a small ball of aluminum, that ball would "flare up" into a pile of slag, aluminum oxide? (kinda like watching a mushroom grow"...
Anyway, I learned how to avoid this by making sure I had a good puddle going by using more heat before adding filler wire . Eventually I got pretty good at avoiding the bubbling blobs of slag creating aluminum balls, and actually made some pretty good looking welds.
Yesterday, I finally emptied the original argon bottle I got when I purchased the Miller 180SD tig welder. $20 later, and I exchanged the empty bottle of argon for a fresh bottle, and what do you know, the problem is not longer a problem!
So it would appear, that my original problem of little balls of aluminum turning into mushrooming piles of slag, was actually a case of "Bad Gas"...
On the positive side, since I learned how to work with the 'Bad Gas' my aluminum welding skills have GREATLY improved, and with the new bottle of "Good Gas" Oh boy can I weld aluminum now,
I'm guessing at this, but I think the 'Bad Gas' must of had some small percentage of oxygen in it. During normal aluminum welding, the cleaning cycle of the machine was able to keep up with the small percentage of oxygen mixed in with the argon. However, if I made a ball, and tried to melt the ball into the base metal, the ball would become so hot, that the production of aluminum oxide was faster than the machine could clean it off.
With the fresh gas, I can take that ball of aluminum and easily melt it into the base metal as needed. However, since working with the 'bad gas' I've gotten real good a timing WHEN to add the filler wire, so the welds look al lot better!
So, I guess its a "win - win" situation.
Thanks again for all the previous suggestion!
Take Care, James Lerch (My telescope construction, Testing, and Coating site)
Press on: nothing in the world can take the place of perseverance. Talent will not; nothing is more common than unsuccessful men with talent. Genius will not; unrewarded genius is almost a proverb. Education will not; the world is full of educated derelicts. Persistence and determination alone are omnipotent. Calvin Coolidge
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