Classical Numismatics Discussion
  Welcome Guest. Please login or register. All Items Purchased From Forum Ancient Coins Are Guaranteed Authentic For Eternity!!! Explore Our Website And Find Joy In The History, Numismatics, Art, Mythology, And Geography Of Coins!!! Expert Authentication - Accurate Descriptions - Reasonable Prices - Coins From Under $10 To Museum Quality Rarities Welcome Guest. Please login or register. Internet challenged? We Are Happy To Take Your Order Over The Phone 252-646-1958 Explore Our Website And Find Joy In The History, Numismatics, Art, Mythology, And Geography Of Coins!!! Support Our Efforts To Serve The Classical Numismatics Community - Shop At Forum Ancient Coins

New & Reduced


Author Topic: Unpleasant result from sodium sesquicarbonate  (Read 4477 times)

0 Members and 1 Guest are viewing this topic.

Offline moonmoth

  • Procurator Caesaris
  • Caesar
  • ****
  • Posts: 2454
    • What I Like About Ancient Coins
Unpleasant result from sodium sesquicarbonate
« on: September 16, 2009, 11:06:32 am »
This is a coin from Neapolis (in Campania) which had a dark green patina over more than half of its surface. It's not the most wonderful specimen, but it could be worse.  When it arrived it had green eruptions in several places, similar to bronze disease but not showing any propensity to give off light green powder, so if bd, then not active.  One spot looked lighter and more powdery, though (bottom left of the lyre), so I decided to give it the usual treatment: simmer for an hour in sodium sesquicarbonate solution.

The result was that all the dark green patina turned light blue .. this really reduced its eye appeal, but there's not much I can do about that now.  The area without that patina hasn't changed much, but now it stands out in contrast rather than blending in.  I tried a cautious dip into vinegar on the principle that acidic compounds are red, alkaline ones are blue; the only result was to clean part of one edge so that the original bronze shone through.  (Bottom right of the reverse.) So I will not try anything else.

So, a note of caution for anyone looking to treat coins with this type of patina.  Balkan patina doesn't mind this treatment one bit, but Italian does!

It does look as though some areas of corrosion have been cleaned out, so I think the treatment was necessary.  But had I known what would happen, I would have chanced leaving it alone to see if was stable.

Coin Type: A bronze AE20 of Neapolis in Campania, c. 250-225 BCE. 18mm x 20mm, 6.41g.
Obverse: Laureate head of Apollo left; Π behind.
Reverse: Kithara leaning on Omphalos, bucranium above. NEOΠOΛIT(ΩN) below.
Ref: Sear GCV 558 var; SNG ANS 531 var.
"... A form of twisted symbolical bedsock ... the true purpose of which, as they realised at first glance, would never (alas) be revealed to mankind."

Offline Aktina

  • Praetorian
  • **
  • Posts: 45
Re: Unpleasant result from sodium sesquicarbonate
« Reply #1 on: October 09, 2011, 05:55:11 pm »
Your coin was treated with a darkener.

It never had an original dark patina.

This why when you treated it with a Sodium bath it faded off.

Non worries.

Before you do anything else, and I do it to all my coins that have BD and have been through a sodium bath.

Give the coin a 20 min 250 degree heat treatment. followed by Ren Wax immediately coins out of the oven.

The heat will darken the coin also, so it will not look as "unpleasant" as it does now.


Offline Aktina

  • Praetorian
  • **
  • Posts: 45
Re: Unpleasant result from sodium sesquicarbonate
« Reply #2 on: January 15, 2012, 12:47:27 pm »
Another alternative for coins like this that I use, is electrolysis.

If the coins looks like it will take it, I will zap the coin to get the rest of the colouring and leave me with a cooper patina.

Then I will use Liver of sulpher, let dry for a coupel of hours, followed by a 30 min 150 F oven treatment to "lock" the sulpher, and then Ren wax it.

NOTE: If the coin is not dark enough for your "taste" when you remove it from the oven, re-apply LOS and this time leave overnight to sit, followed the next day by another 30 min 150F bake in the over, followed by Ren Wax.

Most of the black Greek coins you see in the market are treated this way.

Offline Joe Sermarini

  • Owner, President
  • FORVM STAFF
  • Caesar
  • *****
  • Posts: 12081
  • All Coins Guaranteed for Eternity.
    • FORVM ANCIENT COINS
Re: Unpleasant result from sodium sesquicarbonate
« Reply #3 on: January 15, 2012, 12:58:00 pm »
Another alternative for coins like this that I use, is electrolysis.

If the coins looks like it will take it, I will zap the coin to get the rest of the colouring and leave me with a cooper patina.

Ahg, we discourage electrolysis here.  You may know how to do it well but others that follow your advise will probably destroy their coins.
Joseph Sermarini
Owner, President
FORVM ANCIENT COINS

Offline Aktina

  • Praetorian
  • **
  • Posts: 45
Re: Unpleasant result from sodium sesquicarbonate
« Reply #4 on: January 15, 2012, 08:13:39 pm »


Peopel are equally likley to destroy a coin using chemical and mechanical procedures as they are to use electrolysis

All cleaning procedures should be applied and discussed in a forum like this.

People need to be able to read freely and decide on their own what procedure they should or should not use.

Knowledge is the key. Which door one chooses to use the key on, is up to the idnivdual that holds it ...

Offline areich

  • Tribunus Plebis Perpetuus
  • Procurator Monetae
  • Caesar
  • *****
  • Posts: 8706
    • Ancient Greek and Roman Coins, featuring BMC online and other books
Re: Unpleasant result from sodium sesquicarbonate
« Reply #5 on: January 16, 2012, 11:52:31 am »
Electrolysis is used by people who shouldn't be cleaning coins. Every time in these discussions the same people roll out the same coins they successfully cleaned with electrolysis, then there's a lot of ooh and aah and no one ever shows all the other coins they ruined. Even if they're just common late Romans, there should be some respect shown to these coins, the supply is limited. If you don't have the skill and patience to clean coins properly, don't do it at all. Electrolysis and power tools produce junk for people who don't know any better even though they should.
Andreas Reich

Offline Joe Sermarini

  • Owner, President
  • FORVM STAFF
  • Caesar
  • *****
  • Posts: 12081
  • All Coins Guaranteed for Eternity.
    • FORVM ANCIENT COINS
Re: Unpleasant result from sodium sesquicarbonate
« Reply #6 on: January 16, 2012, 03:59:42 pm »
Peopel are equally likley to destroy a coin using chemical and mechanical procedures as they are to use electrolysis

If I agreed with that, I would not have said anything.  

Knowledge is the key. Which door one chooses to use the key on, is up to the idnivdual that holds it ...

We gain knowledge by listening to people with knowledge.  Perhaps you should give less advice and read more.  
Joseph Sermarini
Owner, President
FORVM ANCIENT COINS

Offline dougsmit

  • Tribunus Plebis Perpetuus
  • Procurator Monetae
  • Caesar
  • *****
  • Posts: 2126
    • Ancient Greek & Roman Coins
Re: Unpleasant result from sodium sesquicarbonate
« Reply #7 on: January 21, 2012, 11:18:44 pm »
We frequently see postings of zapped coins offered as miracles of the cleaning process but to some of us we see only ugliness.  The difference here is our definitions of 'improved' and 'raped'.  In the earlier days of my collecting life there was a term 'brick cleaned' meaning a coin was rubbed on a brick by an archaeologist with no respect for coins other than to date his other finds.  Today we are less likely to brick them and more likely to electrocute them by the batch.  Either way we can read the coin better than when uncleaned and neither coin is desirable in my opinion.

Offline Aktina

  • Praetorian
  • **
  • Posts: 45
Re: Unpleasant result from sodium sesquicarbonate
« Reply #8 on: February 01, 2012, 01:48:56 pm »
Well, I will keep the electrolysis talk for other groups then.  :)

Offline daverino

  • Caesar
  • ****
  • Posts: 543
    • My Gallery:
Re: Unpleasant result from sodium sesquicarbonate
« Reply #9 on: April 18, 2012, 05:31:26 pm »
This is a coin from Neapolis (in Campania) which had a dark green patina over more than half of its surface. It's not the most wonderful specimen, but it could be worse.  When it arrived it had green eruptions in several places, similar to bronze disease but not showing any propensity to give off light green powder, so if bd, then not active.  One spot looked lighter and more powdery, though (bottom left of the lyre), so I decided to give it the usual treatment: simmer for an hour in sodium sesquicarbonate solution.
GCV 558 var; SNG ANS 531 var.


I thought I would extend this  thread and add a note of caution about boiling coins in sesquicarbonate as a "usual treatment" for BD. The solution of sesquicarbonate is very alkaline to begin with and only gets more so with boiling. To oversimplify a bit the chemical reaction in solution is
NaHCO3 <--> NaOH + CO2. The CO2 is boiled off leaving behind NaOH which is lye/drano and you don't want to boil your coins in that stuff (at least, I don't).

Moreover, boiling serves no purpose whatever. The only (slight) use of sesquicarbonate for coin collectors with a real problem of BD (not just verdigris) is to neutralize acid and this occurs instantly without heat. A little soak or wash with baking soda will do just as well. Sesquicarbonate plays no role in removing cuprous chloride which is the underlying cause of BD. Heat will only accelerate the negative consequences of using it without any benefit.

Yes, museums have used sesquicarbonate in some treatments of bronze disease, in conjunction with other chemicals and with very careful monitoring over very long periods of time. I am not familiar with the details but they certainly don't boil their artifacts.

Regards, Dave

 

All coins are guaranteed for eternity