What causes bluing to turn " Plum "??

Hi There,

The older gunsmithing manuals (prior to 1950) I have read blame
the purplish tone on some gun parts one re-blues comes from either
bluing salts becoming too hot (270°F is the approximate bluing temp
but as the solution boils, the water is driven off and the resulting
solution becomes more concentrated and hence, the boiling point
goes up. The purple starts in the 305°F temp and above).

The other cause is very hard high carbon/chromium steels that are
highly polished. They don't like to take a blue and sometimes a higher
temperature is the only thing that will work. At least, these were the
believed causes for the difficulty in taking a blue and thus a plum
color results. At least so the older books say. One technique to improve
Hard, Highly polished parts in taking a blue is to etch the surface in
a weak Nitric Acid solution (10%) for a few minutes or just long enough
to knock some of the 'shine' off.

I have an old Lyman copy (Uberti?) of the 1858 New Model Remington
and it is Purple.

Cheers!
Webb
 
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An update regarding the questionable blue performed on my 29-3 by Ahlman's Gun Shop, in Morristown MN...

I received the gun back and it is much better though the 29-3 isn't 100%, imo. However, the consensus is the issue is the metal and not the bluing process. The gunsmith said he took a bit more time in prepping the metal in particular "more time on the wheel". He did mention there does appear to be some differences in the steel alloys used in the gun, the side plate, crane/yoke, and the frame have a very slight difference in color (it can only be seen in specific light). He also thought there might have been a problem with the original bluing process from the factory. Once the metal was bare he could see a discoloration in the metal "under the glass" that he couldn't help.

All in all, I'm happy with the re-blue. They took care of me. I won't have any issues going back there for my gun smithing or refinishing needs.
 
Alls well that ends well.
If the plum colour on my 29-3 ever bothers me that much Id probably just sell it and use the funds towards another 29-2.

No updated pics?
I just added this pic of an 8,3/8" 29-2 (bottom) from abt 1979 and 6.5" five screw from abt 1956 because it shows the difference in blueing, snapped it at local shop like a month ago
 

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