What IS this gunk?

[dpaul7]

Hi all --

Have been having a problem with one coin - a silvered (I think) antoninianus of Gallienus.  It is covered with the blue/green stuff.... when wet, it almost appears to bunch up when rubbed.  When dry, it gives off little flakes (actuallu little CLOUDS of flakes) just like bronze disease.... I would suspect that, but it has soaked 3 times for 72 hours in Gringott's #1... and been lightly brushed in between. It just stays on. I guess I could just keep on scraping forever.... but it never really seems to go away.

I tried rubbing alchohol to see if it was some sort of paint, no effect... alchohol just acted like water. Could it be BD?

Any ideas?  Hate to let this nice coin deteriorate if it is BD... if it's something else, I guess I could just wax it and be happy with it.  BTW - Please don't tell me it is patina... it does NOT behave like patina!  (Lord knows, I've ruined a few patinas learning!)

Oh - one more quick question -- after soaking in Gringotts for precribed time... if any "green" remains, is it safe to keep on there?

dpaul7

[areich]

It doesn't look like bronze disease to me, neither the colour nor the consistency fit.
Looks like a stripped bronze with perhaps some artificial 'patina'?

[slokind]

If that is really the color, and if it's as hard and solid as you say, and you've also tried acetone (in open air!), then I'm afraid that one of the rarer ancient patinas is a possibility, the way it covers the whole coin, even the edges where not chipped.  It is all a question of soil chemistry and what over the centuries water seaping through the soil has left behind to interact with the metal and the soil.  There are brass and copper cleaners (for use in the kitchen or the church vestry) that are about that color, but no matter how long on the surface and solidified they all should yield to chemical cleaners, even to soap and warm water.  If yours doesn't come off at all, then what CAN it be?  Pat L.

[dpaul7]

Slokind --

I think I did not make myself clear on this issue.

The material covering the coin is not a solid mass.... when wet, it originally seemed like a thin coating of "paint" or something... you could move it around.  The surface coating is powdery..... but will not wash off.

The c oin has soaked in DW for awhile... then 3 sessions in Gringotts #1 to get rid of BD. It does not behave like any patina I have encountered... I am half tempted to just wax the thing and see what happens!

dpaul7

[bruce61813]

" Any ideas?  Hate to let this nice coin deteriorate if it is BD... if it's something else, I guess I could just wax it and be happy with it.  BTW - Please don't tell me it is patina... it does NOT behave like patina!  (Lord knows, I've ruined a few patinas learning!) "

First, patina is the first oxidation layer on the surface of the metal. It can be any color or consistancy. This could be a copper oxide of some type, I have some on cions tha thave been soaking for a year or two, that are bright blue. If you fooowed the instructions and the surface is not a powder that rubs off, it is poboably a copper oxide, and that won't disolve in water very easily. Just leave it alone until it is very dry and see what it does.

Bruce

[dpaul7]

Coin is dry, surface covered in the blue powder. A LIGHT scrape with a dental pick removes powder... in, as I described before, a small "cloud" of dust.  Yet, the coin does not appear to be deteriorated.  I do NOT suspect artificial patina... it cane from a great dealer, and as an "uncleaned".

I will keep a close watch on it!

dpaul7

[bruce61813]

I suspect that it is a simple copper oxide, it is hard to tel from the picture, and dental tools will make alst any thing flake off. Unfortunately , the winter is the dryest air, so BD rare becomes active, but I think it is just copper carbonate.

Bruce

[basemetal]

Also consider that the coin may have been subjected to an amonia "island" bath.  Where the coin is placed on a pedistal of some sort above say a half ounce of ammonia in a sealed container.  One can get a wanted (or un) patina that way and it is indeed thin.  We've seen some altered coins that claim to be from France's chalky soil that have that appearance.