Small question on Mild steel Colours

[ngt]

Ok I tigged a bead of mild steel rod 70s2 on cast iron.
I was wondering why the weld changes colour as i move forward ?
I noticed that by the end where the weld is silvery, the puddle had become quite large, so heat may have build up.
But nevertheless what the correct colour should be ? Black Orange silvery ? Maby the orange is from the copper layer on the mild steel rods ?

 

[3Rs]

When the molten pool becomes large and very bright, Stop welding theres too much heat in the metal. And you get what is known as fall through, this is what has happened on the right.

Where you have too much heat thin metal and not enough rod,
What you should have done was weld half way and stopped until you could touch but not hold the metal.

The colour does give you an idea that your burning about the right. Yes you would be correct in saying that copper shine is the property's of the welding rod. The black would be the oxide of the metal (This shows you are using to high a heat or there is to much heat in the parent metal.

 

[Shox Dr]

I wouldn't of used A15 rod on cast, you need a Dissimilar rod. 316L would get you by