[TheForge] Putting an oxide finish on mild steel?

[Ries Niemi]

> QUESTIONS:
>
> 1. Is this type of oxide finish on mild steel stable in the first 
> place?
> If not is there a way to stabilize it?
>
> 2. I was planning to put a coat of lacquer on the bracket after I
> achieved the desired color. The thought is the lacquer would prevent
> oxygen from attacking the metal further. Does this sound reasonable?
>
> 3. Do you think shining up the steel with a wire wheel is sufficient
> surface prep or is there something else I should be doing?
>
> 4. Is there a chemical/patina treatment out there I can use to achieve
> the desired effect instead of using heat?
>
> 5. Is there anything else you would like to suggest?
>
>


Aaron- as I understand it, these colors are due to changes in the 
reflectivity of the steel on the angstrom lengths- so they are very 
hard to control.
I used to do some production furniture with this finish, and here is 
what I found worked-
I used cold rolled steel. Hot rolled has a layer of real iron oxide on 
it- mill scale- which is very hard, and not shiny at all. So to get it 
to work with hot rolled, you need to completely remove the mill scale. 
A wire brush will work, but I found a flap wheel on a 4 1/2" grinder 
was quicker and easier. I like the blue ones, which are usually 
aluminia zirconia, which is a very tough abrasive.
Once the steel is shiny, you can use a torch, for localised effects, 
like spots, or stripes or squiggles. Or you can try the oven method- 
problem with the oven is that if the piece is all one temp, then it is 
all one color- so not as interesting. I like the control of a torch.
Some steels may not work at all- junkyard steels are always a risk, as 
you dont know how they will weld, heat treat, or color.

After you get it the color you want, you can put a clear coat on it. 
Problem is, most clear coats dont last well outdoors.
Indoors, I used to use clear krylon spray paint, which comes in a matte 
finish, for things that dont get handled much. It needs to be retouched 
every year or so, but it is a pretty minimal finish in terms of 
changing the look.
For things that needed to be tougher, I used either clear rustoleum 
spray paint, or clear powdercoating. Both are glossier and more 
noticeable than the krylon, but much longer lasting. You can get clear 
powder in a 30% gloss, which is not too shiny. But of course, most 
powdercoaters have a $50 or $75 minimum around Seattle. So its not 
really appropriate for one little bracket.

Outdoors, no clear coat will last very long. The best ones are 
expensive, toxic, and a big pain to find and apply. Two part epoxies 
like they use on marine applications are good, and I have heard good 
things about a clearcoat developed for bronze sculptures- but It must 
be special ordered in 5 gallon cans.

there is a nice sculpture inside the aquarium on the waterfront in 
seattle that has heat color treatment on the fishes- but it has a very 
thick clearcoat on it, as it is in a  public space, near salt water.

Steel rusts. Unfinished steel never stays the same for very long. It 
will rust right thru light clearcoats.

Thats why for commercial applications, painting can often cost a very 
big part of the overall budget- sandblasting, primer, and a couple of 
coats of epoxy paint, sprayed on, can easily run a third of a fence 
job's cost.

ries