[TheForge] follow-up on pickling problem

[Bruce Freeman]

The muriatic acid slowly has made progress against the
black scale.  But this is NOT the answer.  The answer
would involve not making the black crud in the first
place.

My initial reaction was that this scale was due to the
flux.  Curiously, the brazed areas seem to have
cleaned up fairly well in acid, for the most part.  

Furthermore, some of the remaining black scale is on
the reverse side from the braze, and high above where
the flux would have been able to flow (due to the
bowl-shape).  

I am starting to believe the black scale may have
nothing to do with flux, and may in fact be "mill
scale."  

Here's the scenario:  I brazed this in a coke forge. 
Lots of carbon near the piece, so it was likely in a
reducing environment.  I speculate I reducet the red
iron rust to black iron oxide = "mill scale".  While
the former is flaky, the latter is hard and
impervious.

If this be the case, the answer is simple:  Clean off
the damned rust before brazing, stupid!  (That's me,
not you.)  

Which is what I'll try next.  Maybe Saturday.  Too
busy today.  This working for myself is tough - the
boss knows immediately whenever I slack off...

Bruce
NJ




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