[TheForge] Fw: Tempering colors

[David E. Smucker]

Tempering colors come from the transparent oxide coating that forms on the 
steel.  The colors are dependent on the 1/2 wave length reflected through 
the oxide coating.  As the coating thickness varies so does the color.  The 
coating thickness varies with temperature and time at temperature.  Without 
the reflection of the "shiny" surface you will not see the colors. (or not 
see much in way of colors.)  You had a mat surface that breaks up the light.

Another place where you see the 1/2 wave length effect is when you look at 
the coating on camera lenses.  This has nothing to do with blacksmithing / 
heat-treating but is an example of the same 1/2 wave length effect of 
reflected light.

Try polishing your steel, and you should see the colors.

Dave

--------------------------------------------------
From: "David Childress" <trollkeep at gmail.com>
Sent: Friday, May 01, 2009 7:54 PM
To: "Blacksmithing List Sponsored by ABANA" <theforge at mailman.qth.net>
Subject: [TheForge] Tempering colors

> I have some hot rolled 1/8 X 3/4 bar stock and I soaked it in muriatic
> acid to remove mill scale and rust.  I tried to heat it from one end
> to get the run of colors as an ornamental finish all I got was a scale
> coating.  Any idea what I did wrong?  I know that the dispay should be
> less impressive than if the metal started shiny but I still think that
> I should have gotten some spectrum of colors.
>
> David Childress
> Rocky Forge Blacksmith Guild
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