Typical Causes of Gas Marks

I'm using Outershield® 71M (E71T-1) flux-cored wire with 75Ar/25CO2. Why am I getting gas marks on the weld surface?

The fast freezing rutile slag on an E71T-1 Outershield® wire gives it excellent out-of-position characteristics, but can also trap gases under the slag as the weld solidifies, resulting in gas marks. Gas marks are more commonly observed welding at high procedures under a high Argon blend shielding gas. Gas marking and/or can be minimized by:

Switching to 100% CO2 shielding gas
Lowering the welding procedure
Cleaning the weld joint of paint, rust and moisture
Minimize any wind disturbance
Cleaning spatter from inside gas nozzle
Increasing the shielding gas flow rate