[TheForge] Putting an oxide finish on mild steel?

[Steve Smith]

Aaron Stavens wrote:

> I had another different piece of sheet steel I had welded on with E6013.
> I had baked it in my kitchen oven and, unintentionally, it acquired a
> dark blue color with purple and copper highlights. There is also a nice
> iridescence in places. My friend saw this and liked it. So, I'm trying
> to achieve a similar effect on the bracket.
> 
> I figured I would buff the bracket with a wire wheel and bake it in the
> oven like I did with the previous piece. The baking didn't go so well.
> All I could achieve was a very light translucent blue even after hours
> in the oven. I assume my oven simply isn't hot enough, but I'm already
> running it at the maximum of 550F. I also tried heating the bracket with
> my welding torch. I achieved a whole rainbow of colors, but I couldn't
> seem to control the colors I achieved.

You're right in describing this as an oxide finish. What happens is if 
you have a thin enough layer of oxide, light hitting the surface will 
interfere with itself (this thin the oxide is essentially transparent). 
This reinforces some wavelengths and reduces others, which leads to colors.

I think what you have might be too thick a layer of oxide, giving you 
the translucent blue. Try running it at several lower temperatures 
(400F? 450F?) and see what happens. Make up some test pieces and take 
them out of the oven at different times.

You might also try heating one end of a shiny piece of metal with a 
torch. The colors "run" along the rest of the piece really quickly when 
you get to the right temperature. It may be tricky to control, even in 
an oven.

Steve