Is there a way to successfully replicate plum bluing with cold blue?

[Forte S+W]

I've always really liked the look of the plum-colored bluing you sometimes see on older firearms, namely Rugers and various Eastern European firearms.

I've heard all manner of speculation regarding how such a phenomenon occurs. Some say it's the result of treating firearms with WD-40 then placing them in storage for extended periods of time, others say it's caused by overheated bluing salts, some say that it has to do with cooling freshly blued firearms in the presence of silicate dust. However, none of these claims have ever really been substantiated.

I'm curious if anyone has ever experienced the phenomenon personally, and whether they have any hypothesis on how it may have occured or how it may be replicated, particularly with cold bluing.

[FrankenMauser]

Getting plum(ish) with cold blue can sometimes be achieved by rust-browning the part/area first, and then cold bluing over the top. But the results are variable, low grade, and .... If you're already rust browning, just rust blue the thing.
I have also seen people use metal dyes to help achieve a plum(ish) color with and w/o cold blue.

But, cold blue sucks. It's a bandaid, and should only be used for short-term touch-up.

--

I asked many firearms manufacturers, several restoration specialists, two metallurgists, and three chemists about plum bluing, while preparing to write an article (which has since been shelved ... for now).

Manufacturers say it's caused by the solvents and oils used by consumers.
Restoration specialists all have the same theories we've seen elsewhere: Contaminants, oils, silicon in the alloy, silica surface contamination, chro-moly alloys, high nickel content, bad salts, cold salts, hot salts, etc.
Metallurgists and chemists ask, "what were the conditions...?" Or, in other words, "it depends."
And I'm more confused now, than when I started.

Bottom line: We still don't know and/or can't agree. It's everything. And nothing.

[Bill DeShivs]

I can personally guarantee that WD 40 doesn't cause it.

[Forte S+W]

@FrankenMauser,
Thank you for the highly detailed response. I would love to read such an article should it ever be completed/published, even if it doesn't reach any definitive conclusion as it is a subject of interest to me.

@Bill DeShivs,
Yeah, I listed that one first because it seems the least likely. Lots of folks use WD-40 for everything under the sun, (Heck, my own father seems to think it's some magical all-purpose spray which can fix anything with a single spritz) so if there were any truth to it, then I imagine that it would have been long since confirmed by the legions of folks like my dad who slather it on everything.

[FrankenMauser]

I can personally guarantee that WD 40 doesn't cause it.

Same here.
Two of my most strikingly plum Rugers have never seen WD-40.
The other 'plums' that I have, I cannot guarantee such (I bought them used). But I've seen no evidence of WD, Ed's Red, or other inappropriate laziness in their past.

.

I've been forming a theory about what causes the plum on hot-blued guns. I think it has a lot of contributing factors. If I figure out how to test that theory without costing an arm and a leg and taking 40 years, I'll finish the article.
I think everyone is right ... at least partially, or in concept.

[Scorch]

Plum color appears in blued firearms because of the composition or condition of the metal itself. A lot of cast and forged firearms will turn plum colored very quickly after bluing due to additives put in the metal to make it easier to cast or machine or for increased strength, others take time and turn very slowly due to hardness or surface treatment of the metal. Hardness of the metal is often a factor, such as case-hardened or very hard firearms (Springfield 1903s are famous for this). Metal alloying is a common factor, you mentioned nickle in the steel, for example early 1900s Winchesters are known to turn plum easily. But most firearms enthusiasts consider plum to be undesirable, so this is the first time I have ever seen anyone actually ask how to turn bluing purple.

[Forte S+W]

I just think it looks really unique and cool. It stands out, but not so much as to be gaudy.

I recently purchased a MilSurp Romanian Tokarev TTC with quite a bit of finish wear and refinishing won't hurt its practically nonexistent collector's value, so I was considering having it reblued, possibly as a DIY project, and was curious if there was a way to purposely give it a plum blue finish.

[Dfariswheel]

The two major causes of plum or reddish colors on firearms are the metal itself, or an out of control hot salts bluing system.

In most cases a purple or red color is a sure symptom of a bluing system that's not under proper control.
Either the chemicals are getting old and depleted, or in most cases, the temperature or chemical mix was off.

You often see red or purple colors done by small gunsmiths who offered rebluing.
These small shops often just didn't do enough bluing to learn how to properly monitor the tanks and just didn't take the care needed to control the process.
What you often got was "off" colors of purple or mostly red colors, especially when viewed in direct sunlight.

Since all gun makers are fully aware that some steels can come out with off colors, they take extreme care not to use those steels known to give problems.

A few times this has caused problems when using a new formula steel casting, most notably with Winchester's post-1964 Model 94 rifles and some Ruger pistols.

Winchester changed much of their processes after 1964 and made a serious mistake with the receivers of the Model 94 rifles.
They chose a cast steel and failed to do adequate research.
These rifle receivers came out of the bluing operation with a horrible Red color.
The only immediate fix Winchester could do was to iron plate the receivers and then blue the iron plating.
This caused some intense stress for refinishers when the polishing operation unknowingly polished off some of the iron plating.
When they came out of the bluing tank they were a disastrous mottled Red/Blue color.

Ruger ran into the same problem with some of their cast steel receivers which came out with a purple color.
Today these Ruger's are often looked for by collectors.

Some known good steels also can get a plum or purple color.
As example you rarely see a Colt or S&W with a purple color because they use only known good steels.
When you do see a Colt of S&W with purple color this is suspected to be guns that were blued when the chemicals were about used up and weren't changed soon enough.

Another case of purple colors are the cylinder releases on some 70's and 80's Colt revolvers.
Apparently Colt had an outside manufacturer make these for them and they were made of a cast steel that often resulted in a distinct purple color only on this specific part.

So, short of a manufacturer using a new steel they haven't researched enough, the major cause of off colors is an out of control bluing operation, with temperature out of line or chemical getting used up.

Some people report a top quality gun that ages to a purple color.
This is usually thought to be a gun blued when the hot salts chemical is getting old, but not to the point where it has a definite purple color when the bluing is still "green" or new.
These pass inspection because under factory lights the color looks good.
However, as the finish ages and oxidizes it starts getting a purple color.

About the only way to get a purple gun is to deliberately run the process with the temperature too high.
The problem is, steels vary so it would be strictly a case of trial and error to get a purple color and not a ugly red color.

[Slopemeno]

In my experience it was lack of temperature control during the hot blue process.

[Dfariswheel]

BINGO, and we have a winner.

As above there are several causes but faulty temperature control is the most common culprit.

[Forte S+W]

Is there any idea of what temp bluing salts begin to produce a reddish hue? Or how hot they'd need to be in order to achieve such results?

[Bill DeShivs]

That's like asking for a bad paint job on your car!

[Forte S+W]

I honestly prefer the look to conventional bluing. *shrugs*

Furthermore, in my opinion, many modern automotive paint jobs are awful. Everything is all metalic, glossy, and reflective like a foil trading card. And don't even get me started on the selection of colors which range from bland to outright gaudy like Cough Syrup Orange, so I'm quite certain that my taste in automotive paint jobs is considered bad as well.

[Dfariswheel]

Trying for a purple color would depend on the type and heat treating of the steel.

This would require experimentation on the SAME steel and heat treating to figure out the ideal temperature and time.
That's going to be a problem because it would require stripping off the failed finish for another try.
Every time it's polished off you loose some metal and definition of the lines and edges of the part.

Unless you're willing to buy the expensive equipment and set it up in a separate room by itself, I don't know of any refinisher who will attempt this.

You have to put hot salts bluing systems in a special room or set up outside under cover, because the highly corrosive fumes will attack and rust any steel in the room, such as plumbing and wiring.

Deliberately doing a purple blued finish is just something no one ever figured to do, since it's a sure sign of a bad blue job.

The only other option I know of would be one of the colored epoxy or polymer gun coatings like Cerakote or Lauer Duracoat.
That's not going to look like colored steel because it's a coating.