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Dear Aaron and Marianne,


I can certainly say from my experience that this corrosion is, in general, not following slip traces, crystal planes, or even grain boundaries. Another thought is that the corrosion need not be directly bacterial in origin. The decay of bodies can have some interesting effects on corrosion of grave goods. Perhaps also relevant, I am at the ,moment working on the metallography of the bronzes from the burned out Late Bronze Age village of Must Farm in the fens near Peterborough. The bronzes have to a varying degree been affected by fire and then deposited in environments which vary from anaerobic to relatively normal burial conditions. The corrosion microstructures are very varied but I am only just getting started. 


Another area of interest is the copper sheathing of 18th and 19th century ships: British copper can contain up to 1% arsenic and 1% bismuth (the latter is always as oxide) , and the deterioration of the copper was always of interest to the Navy but there a factor is also erosion through the passage of the hull through the water.  Sir Humphrey Davy's last ever paper for the Royal Society was on this topic. I have not seen this filamentary corrosion pattern in any marine copper. 


Regards,

Peter




From: Arch-Metals Group <[log in to unmask]> on behalf of Aaron Shugar <[log in to unmask]>
Sent: 13 February 2019 14:37
To: [log in to unmask]
Subject: Re: Bacteria induced corrosion on Cu-As objects
 
Marianne,

I have to agree with Peter. The work that I have done and seen on microbial deterioration of copper from SRB is fairly restrictive to the surface as either channels or individual pitting. Copper and arsenic are biocides and it would be odd for bacterial penetration into the metal in the way you have seen it.  I would suggest etching the section to see the extent of working and grain structure. You might find that the corrosion is following those paths.  If you contact me off-list I can send you some articles that deal with biodeterioration of copper.  There has been extensive study in modern industry with specific concern for copper pipes.  the journal Corrosion has some excellent articles on this.

Aaron

Aaron N. Shugar, Ph.D.
Andrew W. Mellon Professor of Conservation Science
Patricia H. and Richard E. Garman Art Conservation Department
Buffalo State, SUNY
Rockwell Hall 230
1300 Elmwood Ave
Buffalo, NY 14222
Ph: 716.878.5025 
Fax: 716.878.5039
E-mail:
[log in to unmask]

http://artconservation.buffalostate.edu/





On Wed, Feb 13, 2019 at 6:07 AM Northover, Peter <[log in to unmask]> wrote:

Dear Marianne,


A little quick checking and my impression is that I have seen that corrosion structure in bronze but not that I can think of in arsenical copper. I think I may have seen an example where the corrosion is more related to the microstructure suggesting some typical transgranular corrosion had started and then the mechanism changed. Have you done any elemental mapping on the corrosion tracks? I know I haven't because the post-ex projects where I have seen it were not that well funded.


Regards,

Peter




From: Arch-Metals Group <[log in to unmask]> on behalf of Marianne Mödlinger <[log in to unmask]>
Sent: 07 February 2019 07:26
To: [log in to unmask]
Subject: Re: Bacteria induced corrosion on Cu-As objects
 
Dear Peter, dear all,

please find some bright field images of Cu-Sn objects following this link (pdf download):

These structures seem to be most likely related to bacterial corrosion (see links below).
I would be very interested in any such structure noted in archaeological Cu-As objects.

All the best,
Marianne





Am Do., 7. Feb. 2019 um 00:17 Uhr schrieb Northover, Peter <[log in to unmask]>:

Dear Marianne,


It would help if you provided bright field images as well. I think I have seen things like that but have no interpretation for them as yet.


Peter Northover




From: Arch-Metals Group <[log in to unmask]> on behalf of Marianne Mödlinger <[log in to unmask]>
Sent: 04 February 2019 16:56
To: [log in to unmask]
Subject: Bacteria induced corrosion on Cu-As objects
 
Dear list members,

I wonder if somebody has noted similar corrosion structures in Cu-As alloys, as visible here:


(the images are in polarized light and derive all from Bronze Age Cu-Sn objects).

Thank you very much for any help!

All the best,
Marianne


--
Mag. Dr. (habil.) Marianne Mödlinger
Homepage & blog ArsenicLoss
+39.340.1388.506 (Italy),
+33.(0)680.54.41.90 (France)


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--
Mag. Dr. (habil.) Marianne Mödlinger
Homepage & blog ArsenicLoss
+39.340.1388.506 (Italy),
+33.(0)680.54.41.90 (France)


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