Bronze disease question

[Akropolis]

Something that has been nagging at the back corner of my mind is how copper/bronze ancient coins survive for centuries in soils of various composition and moisture, with bronze disease not kicking-in until after excavation.

Perhaps countless millions of such coins have disintegrated in the soil from bronze disease over the centuries, while others have not.

Specifically, if FORVM members include metalurgists or similar disciplines, is bronze disease aerobic? Could it be that it was triggered by finders cleaning the coins in chlorinated water?

Perhaps the answer is "all of the above."

Curious,
PeteB

[slokind]

A Romanian once told me that modern fertilizers and modern plows practically guarantee the destruction of loose coins unless rescued before the corn was green, so to speak.  Of course, he was a detectorist, but I daresay he was right, too.  Pat

[bruce61813]

Something that has been nagging at the back corner of my mind is how copper/bronze ancient coins survive for centuries in soils of various composition and moisture, with bronze disease not kicking-in until after excavation.

Perhaps countless millions of such coins have disintegrated in the soil from bronze disease over the centuries, while others have not.

Specifically, if FORVM members include metalugists or similar disciplines, is bronze disease aerobic? Could it be that it was triggered by finders cleaning the coins in chlorinated water?

Perhaps the answer is "all of the above."

Curious,
PeteB

 It is very untrue that coins have survived for centuries without damage and 'modern' use of fertilizers have caused problems. Look at the PMS COL VIMS , a very large percentage of those found are in poor condition, and they come from areas that are poorly developed or not even used for agriculture. Even the UK has problems with ancient coins, and many turned in are from low tech farming.

 I have also received coins from deep desert regions that were never used for farming. Fertilizer is mostly nitrogen, more especially ammonia, that is a base, and has little effect on copper based materials. 

Take two slugs, or modern pennies, weigh them, put one in straight vinegar, the other in ammonia. seal the containers and let them sit sor 6 months and measure the changes. That would give you an idea.

Bruce

[napki]

Soil and fertilizer not make so big the BD problem as much as does the quick and careless acid cleaning in source country.

[bruce61813]

In general. BD is not caused by cleaning methods. Even using acids to clean, with the exception of HCL, won't cause BD. HCl can, but it would need to be rinsed or washed, as the coins could not be handled. The real problem is the embedded salts that accumulate over the centuries and are left deep in the fabric of the coins matrix. These react with atmosheric moisture to for the HCl that causes BD. In dry, arid places, BD will generally not appear, but when the coins are moved to areas of high moisture, the BD will be triggered.

I often wonder how many museums and universities that do archaeological work have uncleaned coins in their storage areas, uncleaned and non-atmospherically controlled, that are being 'eaten' by BD.

Bruce

[areich]

There was some German museum that had put part of its collection online, it was a depressing sight
but I don't remember who it was.

[bruce61813]

Several years ago, there was a member of Forum that was working for a Danish Museum to put their collection on-line, it was doing well, but I have long forgotten who it was, information ma still be here in the message archives. but they were doing a good job of it, and had some very nice coins.

Bruce