Date:         Thu, 2 Jun 2011 20:24:55 -0400
Reply-To:     David Beierl <dbeierl@ATTGLOBAL.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         David Beierl <dbeierl@ATTGLOBAL.NET>
Subject:      Re: CV Joint ?
Comments: To: Don Hanson <dhanson928@GMAIL.COM>
In-Reply-To:  <BANLkTinFwJmRSaeFTN9rp09gW_XmcgqjzA@mail.gmail.com>
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At 07:31 PM 6/2/2011, Don Hanson wrote:
>for re-greasing and the balls were blue and pitted

That blue is an "optical color" caused by a film of oxide (that we'd
call rust if it were thicker) so many wavelengths of light
thick.  Just like when you're grinding a carbon steel tool or blade,
it means that the steel is now much softer than before, for some
appreciable depth.*  In other words, history.  The pitting is a result.

*it's just an indicator.  If the steel's gotten hot enough to grow
that thick a layer of oxide, it's lost enough hardness to no longer
be able to take an edge.  As the layer builds up it goes from pale
straw to dark to purple to blue and then sky blue, as the thickness
of the layer causes different phase interference of the incoming and
outgoing light.  Good photo here:
http://www.thecarvingpath.net/forum/index.php?/topic/945-notes-on-heat-treatment-of-carbon-steel/
search the page for Temper Colors (about halfway down).

Yrs,
d