Need info on mint's annealing furnaces

The thread on milk spots made me consider the annealing of the planchets before striking. I found the statement that the SF mint now uses a process of annealing in a mixture of ~ 96% Nitrogen gas and 4% hydrogen gas at high temperatures

"Unlike the days of old, SF Mint annealing furnaces are environmentally friendly even as blank molecules are excited in an oxygen-starved environment at temperatures ranging from 1050 degrees Fahrenheit to 1650 degrees Fahrenheit. For the technically minded, oxygen deprivation is necessary to minimize blank oxidation. The actual atmosphere within the furnace chamber is a combination of nitrogen (~96%) and hydrogen (~4%)."
http://www.coinnews.net/2013/04/03/u-s-mint-at-san-francisco-preparing-coin-blanks/

My thoughts is if ammonia gas is produced ( the temperature could be sufficient), but since it appears not to be under significant pressure, I am not sure. My train of thought is that if some ammonia was produced, other chemicals might be used to eliminate the odor within the mint, such as sodium bicarbonate or acetic acid, [common use]producing mainly odorless ammonium salts such as ammonium acetate or ammonium bicarbonate. Ammonium bicarbonate is insoluble in acetone and alcohols, but the acetate salt is soluble in both. Thus I would suspect the bicarb more.

Ok, here is my questions.

1. Anyone been in the SF mint last few years that was told anything about the annealing overs that use a non-oxidative atmosphere, or any ammonia smells noted?

2. Does the Philadelphia and WP mint use the same new ovens?

3. What is the oldest .999 coin with the spots you know about?

If this is a false track, the history and makeup of anti-oxidizing solutions seem to be the next area that could cause the spots.

These seem to be the 2 main areas that could change recently

Thanks,
Jim

 

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I'm following this thread. My thoughts are that since "sintered" or improperly annealed planchets are still not completely understood or explainable despite heavy publicity for and concerted effort to trace the conditions leading to them (black beauty nickels) and somewhat common appearance on the market, and inquiry in this direction will leave us wanting.

I always heard milk spots being attributed to improper wash?

 

I have not been satisfied on this, as I have not been able to find of what this 'wash' consisted, and why it would form a insoluble metallic spot occasionally, but not always, and when it was initiated or changed at mints. sorry a lot of questions.

 

The other thing is that the quote source above says the mix is ~96% N, and 4% H, but other gas mixtures such as this used in other annealing machines is 75%N, 4% H, and 21% unspecified.

 

My friends work at a foundry. Every car in the parking lot gets covered with hot metal shavings that burn into the paint.

Perhaps something similar is occurring here...

 

I am missing something here. If you are suspecting these spots are ammonium carbonate or acetate, shouldn't water or at worst salt water remove then?

 

If a coin blank is "improperly" annealed, doesn't it trap tiny amounts of annealing fluid(s) in fractures present on the surface? To me, a milk spot has always looked like a "leak" of something from below the surface. Just an observation.

 

Perhaps it would be wise to research the Royal Canadian Mint as well. Their silver maple leaves have that problem.

 

That is farther down the chain, I need to determine if there are early indicators that ammonium compounds are even produced by the newer annealing ovens ( i.e., present in the other mints, and ammonia being produced), or I need a different suspect.

I have not seen extreme photographs of the coin surface of a 'milk spot', with a SEM or similar. If you have a link, I would like to see them. I also notice d in some of the mint releases, pictures of the cross section devices they use to insure that the metal grains are even distributed, I would suspect that would eventually show up in a 'lucky' slice.

Actually a quote on this site about how they knew about it, and since it was a bullion coin, ( basically ~deal with it), made me think it wasn't just a wash solution makeup , as that could be changed out but an expensive, difficult to replace, etc, piece of equipment like new annealing ovens. The new ovens should reduce other problems in the process such as premature oxidation -thus changes of the planchet surfaces. I am doubtful that the mints build their own, so some manufacturer has a niche and not a lot of competition.

Any information on the mint's ovens would be interesting. I have ASE coins from the first to 2015, about 150+, and no spots. Also some foreign bullion .999 or .9999, and no spots. Small sample number I know, but indicates more than one factor perhaps.

Not saying the question as to origin can be solved, but maybe more isolation of the problem, but my suspicion is that it will remain, as to cause and activation on stored coins.

 

http://www.pal-item.com/story/money/2014/10/25/local-company-national-us-mint-player/17900015/

According to this article the new annealing ovens are in Denver and San Francisco.

 

Thanks Yankee, that is an interesting article. I can start searching for patents filed by the company.

Analysis of the spot composition would be a tremendous help with the problem. I am certain it has already been done, either by the mint, PCGS, or others that have their hands on devices which can isolate the process to just the spot area.

Both the 'reappearance' and 'time to develop' are curious, but not unexpected for chemical reaction. Most reporting such on the forum do not seem to indicate that they observed and increasing in size effect. Most just say they were 'suddenly there', so much of objective input is missing such as initial appearance, growth rate and conditions, etc.

 

The temperature is high enough for ammonia production, but to produce it they also use a catalyst and high pressure (200 bar). At the low pressures in the furnace I would expect any ammonia production to be extremely minimal.

 

Can anyone here actual confirm that these spots just “appear”? I’ve only heard the TPG’ers claim they appeared after they graded the coin.

 

I had a 2014 proof ASE (West Point mint) that got worse with time.

 

I can only offer this. I watched Mike Ellis write a "refusal to sticker" note at the QA[check] booth for an MS70 MS (non-proof) ASE at Portland. He handed it to me. It was so loaded with OBVIOUS milk spots that if they were there when PCGS graded it, not only should the grader not be grading, he should have his driver's license lifted. I can only conclude they "grew" after the slabbing.

 

Perhaps you could do a FOIA request for the solutions used to clean the blanks anyway.

 

Did you try to present these questions to the mint?

 

Silver Hydride is not desolved by acid and is white as milk.

 

It will dissolve in ammonia