sometimes hot blue shows the different metal, but rust blue is usualy the same color across the board.
TIG allows you to do very precise welding and not use an obscene amount of heat on the part. You have more finesse with a TIG rig than any other kind of welding, so you can do things such as weld individual pits, weld 2 razor blades together, and other very detailed work.
I use pure argon, as does every other custom maker with whom I have spoken. Also use 1/16" 2% thorinated tungsten and 1/16" filler rod of various alloy. I also use a foot control rheostat for the amperage. You can weld with as little as about 5amps of current. This allows you to add just enough heat to the part to get the puddle and fusion you need, but no more.
Another benefit is that welds are very "clean," assuming you haev done everything correctly. This is critical when doing highly finished custom work.
TIG has replaced oxy/acetalene welding in gun work just as forge welding was replaced many, many years ago.
