I found a used colt 6920 at a local shop for a really good price. Gun doesn't appear to be hardly used at all. However, it does have a strange "splotchy appearance on once side of the barrel. It does not appear rust, rather a mottled discoloration where the parkerized finish is sort of spotty. The spots are a either "whiter", "greener" or "browner" in color than the standard grey of the phosphate finish (Although the variations are slight). Any thoughts on why that is...I have never seen one like that.
"splotchy" parkerized finish on ar barrel.
- Thread starter Servo77
- Start date
It's possible there's something on the barrel that will wipe off with an oily rag. I'd ask the gunshop to do that for you then look at it. Parkerizing is like a sponge and will absorb most any liquid it comes in contact with. Could be solvent or something from the last owner.
jglsprings
New member
+1
That was my first guess. Don't ask me how I know.
warbirdlover
New member
Knowing a little about "manganese phosphate" or "oxide" coatings I can say a few things about what causes the blotchy appearance during coating. I used to "monitor" the phosphating bath for a large company (was a metallurgist).
1. The phosphating "bath" not being controlled (free acid and total acid) by adding enough iron. The "free acid" gets to high and it doesn't coat evenly (blotchy) and in extreme cases can pit the metal (etching).
2. The acid level gets too low.
3. Parts are not cleaned properly before going in the bath. (Oil can inhibit the process).
In either case there is no way to fix except re-run.
I still remember coming in to work in North Carolina (I was a relocated Yankee) with my other shift guy yelling (in a real southern accent) "It's etchin... it's etchin". (We used to coat gears with it). It was pretty funny.
Forgot... Parkerizing is a trade name for manganese phosphating because the most common product is made by Park Chemical Company. Another company making the same stuff calls their product Granodine (granodizing). And zinc phosphate coatings are thinner and a grey color. Magnanese phosphate coatings are black and heavier.
1. The phosphating "bath" not being controlled (free acid and total acid) by adding enough iron. The "free acid" gets to high and it doesn't coat evenly (blotchy) and in extreme cases can pit the metal (etching).
2. The acid level gets too low.
3. Parts are not cleaned properly before going in the bath. (Oil can inhibit the process).
In either case there is no way to fix except re-run.
I still remember coming in to work in North Carolina (I was a relocated Yankee) with my other shift guy yelling (in a real southern accent) "It's etchin... it's etchin". (We used to coat gears with it). It was pretty funny.
Forgot... Parkerizing is a trade name for manganese phosphating because the most common product is made by Park Chemical Company. Another company making the same stuff calls their product Granodine (granodizing). And zinc phosphate coatings are thinner and a grey color. Magnanese phosphate coatings are black and heavier.
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