Welding Tips and Tricks

I am fabricating quite a large sculpture out of 90/10 copper zinc sheet. The rods are SIF phosphor/bronze which I think are 7% tin and 3% phosphor. Gas is Pure-shield Argon.
I am getting a hard yellow crystal deposit on the electrode, typically on the tip of the point and also just inside the cup.

Am I right in thinking that this is tungsten oxide?

If so, what is the probable cause? I have experimented with turning the gas flow up and down and the regulator has a flow meter. I have also experimented with the post flow. Neither seems to make much difference.

Second question
There is a noticeable variation in the quality of rods. Some rods weld beautifully, forming a shiny puddle that is easy to manipulate while others have a puddle that is full of dark spots that barely wets out the base metal and has little fusion.
At first I thought this must be a dirty electrode, unclean base metal or gas shortage etc, but if I pick up a half used good rod changing nothing else, it welds away fine. Is this a common problem?

Nick

I never tried this & almost never Tig braze so if someone else chimes in with much experience go with they're thoughts ! - but the fact it's yellow would suggest it's zinc from the base metal - I don't think gas cover will have a significant effect on this unless your really short on flow / cup size ( I would use gas lens with at least an 8 cup ) - I think it could be just how much heat build up in the part your welding - could be worth trying doing short runs as fast as you can go with a heat sink nearby if possible - anytime you get an alloy containing zinc too hot some of it boils off - or at least it does for me !

I don't think it's zinc. Some always boils off but the yellow crystals seem to form most when the welding is clean. I don't always get them, usually it happens on longer runs when I'm welding after tacking up. In any case, wouldn't the electrode be too hot for zinc?

It's a sculpture in two parts, each weighing about 300kg, mostly copper, so no need for a heat sink! Actually sometimes I really struggle to get the welds hot enough. The faces are made by folding and the folded edges are left inside as stiffeners but they also make effective cooling fins.

The photo of tungsten oxide in wikipedia ( http://en.wikipedia.org/wiki/Tungsten_trioxide ) looks very similar to what I'm getting on the electrode.

Sorry I have no further insight - but if we bump the question every few days so it does'nt get buried I'm sure someone here has experience that will help - just takes a while sometimes for the right person to read it - in the mean time I think Kevin Caron does similar work on sculptures - maybe worth trying to contact him - he always seems a nice / helpful guy.

Thanks..
I'll try to get a photo. The structures are complete but I still have work to do on the faces. It's partly just curiosity, but also as I mentioned about half of one of the batches of rods we bought were almost impossible to weld with. They are very gassy as though there was no argon flow. It doesn't look like zinc fume coming out and since inevitably you end up breathing some of it I was concerned to know what it was!