Author Topic: Acute BD problem  (Read 1353 times)

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Offline Pellinore

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Acute BD problem
« on: July 24, 2016, 01:28:13 PM »
Dear Bruce,
I have a serious BD problem in these two rare coins of the 7th century. The left one, a rare Arab-Sassanian pashiz measuring only 14 mm, I only bought a short time ago. It arrived with a little speck of BD, and now it breaks out seriously. The other is a billon or potin Hunnic imitation of a Sassanian drachm that I had for about a year, then a little green spot started breaking out. I put both coins into the double-soda mix according to your recipe, but I didn't dare put them in long. Of the pashiz, the surface started crumbling, whereas the drachm started to rust. The billon is obviously an unclear mix of metals.
What can I do about this? Some advice I received:

try a watered-down lemon mix, then a layer of wax;
or, try a distilled water bath, then an acetone bath, then bake the coin in the oven on a piece of aluminum foil (in fact, that advice was for another coin, a silver fourrée of the same age, also with BD).

How can I preserve these coins?
-- Paul

Offline bruce61813

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Re: Acute BD problem
« Reply #1 on: September 16, 2016, 02:23:27 PM »
If you have access to baking soda and washing soda, mix them 1:1 , use 17 grams of this mix in 350 ml of very hot water. Allow the coins to soak for 24 hours, then scrub with a old toothbrush. I would continue the soaks for at least 2 weeks. It takes time to get the salt out of the coins matrix. If you can keep the water warm [I use an old coffee maker that keeps the solution at about 120 - 150 degrees Fahrenheit. This helps  speed things up and is not hot enough to be dangerous.

The nice thing about the soda solution id it will not harm either the bronze/copper or silver.  there is a commercial product called  "Bronze Disease Killer" available from https://www.nobleromancoins.com/product_info.php?products_id=202.
 I know this works, as I developed it and make it for Kevin. The packet is 8 ounces and makes a lot of solution. It can be mix with water an stored in a capped brown bottle [preferred] or simple mixed one cup at a time. the powder form lasts a very long time.

Bruce
« Last Edit: September 16, 2016, 02:58:53 PM by bruce61813 »

Offline bruce61813

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Re: Acute BD problem
« Reply #2 on: September 16, 2016, 02:50:52 PM »
added thoughts: Don't use lemon juice on the copper/bronze coins. It doesn't harm the silver, but use it carefully. Bronze disease is caused by NaCl and atmospheric moisture forming among other things HCl acid. For the full explanation see  http://www.worldofcoins.eu/forum/index.php/topic,134.0.html. Look down the threads and you will see the paper I wrote.

Bruce

Offline Pellinore

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Re: Acute BD problem
« Reply #3 on: August 27, 2017, 02:13:37 AM »
I kept the nice little Arabo-Sassanian coin for a year in the solution (mostly). But somehow it doesn't really work. It gets bluer slowly. I'm afraid I'm losing this rare coin.
-- Paul


Offline bruce61813

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Re: Acute BD problem
« Reply #4 on: August 27, 2017, 03:48:28 AM »
Did you scrub the coin between soaks? You need to change the solution at least once every 4 days, and give the coin a light scrub  [nylon or brass brush], every 24 hours. This removes neutralized surface material and exposes a new surface.

Under normal conditions, 6 weeks is the longest I have had to soak a coin. Also, don't let the solution dry out, you can add water as needed.

Bruce