World of Coins

Collecting coins => Cleaning, conservation and storage => Topic started by: Pellinore on February 17, 2021, 09:30:44 AM

Title: How could one treat a Sasanian lead coin?
Post by: Pellinore on February 17, 2021, 09:30:44 AM
In the course of 2019-2020 a number of (formerly very rare) lead Sasanian coins came onto the market. These are small and unremarkable, having the same types as the small copper coins. I bought a few of these in mediocre condition, but they all came with white encrustations. Would it be possible to do something about this safely? For instance, this one, a pashiz of Shapur II, much like a pashiz (https://www.sarc.auction/SASANIAN-KINGDOM-Shahpur-II-309-379-lead-pashiz-3-16g-NM-ND_i21236261) from Stephen Album, that has even more white on it.

On the reverse of my coin, there appears to be some lettering at the sides of the altar attendants that I'd like to study.
15 mm, 1.80 gr.

-- Paul

Title: Re: How could one treat a Sasanian lead coin?
Post by: THCoins on February 17, 2021, 03:22:15 PM
I'm not a chemist. But if you have several, you might just experiment with the most far gone specimen.
But offcourse, no experiment without risk ! Leadcompounds may be toxic also through skin contact !

I can imagine the surface material consisting of leadsulfate, leadoxide and/or lead carbonate.
What I would try first is brushing in a weakly acidic watery solution.
Title: Re: How could one treat a Sasanian lead coin?
Post by: bruce61813 on April 08, 2021, 04:06:00 PM
I am not sure of lead, but you might try electrolysis. Low voltage [6 vdc] and use baking soda in the water. Do not use salt, NaCl, it conducts too well and could "burn" the coin. The soda conducts less and slows the reaction. Be very careful of dist from these coins, lead dust is very toxic.

Bruce
Title: Re: How could one treat a Sasanian lead coin?
Post by: otlichnik on April 11, 2021, 08:58:07 PM
It is VERY difficult to clean lead like this.

I have never tried anything chemical, only mechanical.

Soaking in distilled water and working away gently with a bamboo skewer sometimes removes a bit of the white stuff.  Sometimes not.

I have removed some of the tan adhesions very very carefully with a scalpel.  But it is very easy to nick the actual lead. 

Instead of cleaning you might be able to get a better indication of the design by pressing it into soft plasticine or silly-putty and studying the reverse impression.

SC

Title: Re: How could one treat a Sasanian lead coin?
Post by: Figleaf on April 11, 2021, 09:41:44 PM
With all respect, I have to disagree. I have worked with making impressions and using pencil mine powder to make details stand out and learned the hard way what is actually easy the understand: an impression cannot possibly be better than the original. You always lose detail.

Experimenting is fun, but how do you choose the coin you are willing to sacrifice if you don't know what exactly is underneath the crud?

My experience is that if you happen to bump into a person who cleans metal objects for museums for a living, they are happy to discuss your problem and suggest solutions as long as you keep it private. They often don't know either, but at least they have experience and books.

Before COVID-19, I would sometimes meet such people at numismatic meetings. Now, it probably takes some determined phone calls to a museum (don't be shy, start with Rijksmuseum; they must be bored these days anyhow, next, try Arent Pol and Paul Beliƫn. They ought to know who to trust with curating metallic objects. If you wish, I'll try a Curator Emeritus of Islamic Coins, American Numismatic Society for you.) to get a name and a phone number. Your case is good. You are an advanced collector and the items are very old.

You may try to make a deal with the museum: your duplicates or access to your whole group for their curating help, maybe not as crudely explicit as all that, but an implied promise in your voice might help. "Hey fellows, I am a collector, an amateur, but if I can help you in turn I will" or "I'll study the items and send you details about what I found if that is of interest to you." or more vaguely "I have a little group of them; I don't think they have been studied before".

Peter
Title: Re: How could one treat a Sasanian lead coin?
Post by: bruce61813 on April 12, 2021, 03:02:16 AM
I ran across this, it may help. " use 30% vinegar, 70% water, heated at 180 degrees F (82 deg C) for 5 minutes and then rinsed in room temp clear water. Followed by a soak soda & water solution to neutralize any of the vinegar ."
 Note: this was suggested for oxidized lead fishing weights and cast lead bullets.

Bruce
Title: Re: How could one treat a Sasanian lead coin?
Post by: Figleaf on April 12, 2021, 11:54:05 AM
If you want to use that method, stay with the coin, neutralise as soon as you are happy. There is a danger of going overboard and losing detail that does not have a risk equivalent when working with fishing weights :)

Peter