As the title states I had someone parkerize an AK and the finish turned plum.  Any ideas of why?  I'm guessing a contaminated solution but contaminated by what?

I've done parkerizing in Zinc and Maganese.  Properly done Zinc will yield a grey color while Maganese will leave the parts a darker color that appears almost black in color.  There are a few things to consider when doing parkerizing.  Some solutions require "seasoning", meaning the first time you heat it up, put a clean steel part in the tank and allow the solution and metal to do it's things and heat up.  The first time your part may be lighter in color.  Let the solution cool down and parts from future batches should come out darker.

I use Brownells Maganese and the first batch, I toss in a small piece of de-greased steel wool and heat up the solution.  The solution can be re-used as long as the acid strength is adequate.  Some solutions can be used for quite a while before the whole tank is dumped out or if more solution is added.  Once a part has been parked, it should be rinsed in a neutralizer solution such as water mixed with baking soda and then a water displacement oil is sprayed on the part.  I use WD-40 since it's readily available and cheap.  The plum color on your AK can be from parkerizing solution mixed with cosmoline or trace contaminants of it.

If you're not happy with your finish, degrease, abrasive blast, and use a clean seasoned solution.

Here is the picture the builder sent me.  He's still new to parkerizing.  So i was thinking some sort of contaminate from his in solution burners.  Of course now he has tons of people who want "plum" AK mags from him...

I'd ask the refinisher what solution he's using (Zinc or Manganese).  The pic looks like Zinc 9as long as his solution is correctly seasoned).  Zinc is used quite a bit for M-1 Garand and M-1 Carbines, while Manganese is used for darker or blacker shades.

WOW - that is purple!

I've seen greenish park before, and YEARS ago someone at Knob Creek would park in colors (I watched a woman get her STEN parked in a pinkish color ... but your gun is definitely purple).

I have no idea what they used, but as the other posters said zinc and mag are the common.

I would want that AK reparked!  The uninformed might think its rust.

He's using manganese as his first few items came out nice and black.

He is using an in tank heater, so I wonder if the in tank heater is introducing contamination as the solution ages.  Have not seen it in person and most park setups I've dealt with were external heaters.

He has offered to repark it for me.

Damn that looks awesome! I'd  keep it that way.

Bet he couldn't reproduce that if he tired

My guess would be his solution is weakened and the acid ratio has dropped or he may need to "re-freshen" his solution by adding a small piece of oil free steel wool and run it by itself for a few minutes to let the steel dissolve and let the tank cool down, then re-park your gun.  I've had best results when I place parts in my tank when the solution begins to barely get warm and use medium heat rather than dipping cold parts into a hot boiling solution.  It seems the longer dwell time works better for me.  Some will say just heat it up but my own experience works best for me.

This is from copper contamination.  The copper can be from brass or bronze.  When I first started parkerizing, I used a stainless tank that had a brass drain valve on it.  The first few jobs came out fine.  Some time later, everything came out plum/purple.  I didn't realize where it was coming from until the parkerizing solution actually eroded that drain valve enough that it fell out and drained on the floor.

Since I welded up an all stainless tank I've had no more problems with this.  Sounds like your guy's tank heater has exposed copper elements.

Copper contaminated manganese phosphate:


Clean manganese phosphate:

Now to decide whether I want to keep the rifle like this as it's quite unique or wait and get him to re-do it once he gets his tank squared away.

That looks pretty cool, I'd keep it as is.

Looks like too little parkerizing solution to water ratio. Or left the parts in the neutralizing water too long. I did a lot of parkerizing at Barrett.

Your finish is going to look a lot rustier before long.

Looks way cool. I'd keep it as-is unless it will somehow affect it over time.

ETA: just saw this is 2 months old.

Kuraki is likely on to something and those blades look awesome!