From: Jon Elson

Sometimes
I touch the electrode to the metal, but that contamination
burns off after a few seconds, it seems.

In addition to what Ernie has said I would advise you to not continue welding
after you contaminate the electrode. Stop, clean it, resharpen it and then go
back to work. You can get an accumulation of metal deposited on the inside of
the cup that boils off the electrode when you continue welding after you
contaminate the tip.

Richard Coke