27 out of 234 days: surface ‘enhancements’

I’ve just finished up here at Rutgers and am waiting to discuss my early findings with a colleague, but I have some extra time before he arrives.

I’ve wrapped my head around zinc levels to be satisfied that in a few cases I can reject specimens from my analyses when levels are far too high. The other big interference is Light Elements, basically oxidation. All those readings go out the window too, even when I think the specimen is likely genuine. I do leave them in for other fabric analyses. But then what about other unexpected elements that keep coming up. The list of modern patina chemicals given below is quoted directly from the Newman Portal.

This type of ‘enhancement’ might explain to some degree some of the odd stuff I’m seeing, including perhaps some of the light elements (N, H, O etc…)

A big one that has been turning up is SULFUR. Obviously it could be naturally occurring from the conditions of deposition. Italy has TONS of the stuff. Campi Flegrei ?! This sort of interference from natural incrustation is my first assumption when I turn loads of CALCIUM as well.


[That news came in as I was typing: had to share in real time.]

The other thing that shows up is CHLORIDE which is associated with bronze disease. On some specimens I suspect it is in fact bronze disease, but I wonder if in some cases it might be ‘enhancement’. Wouldn’t the use of this in patina creation be a bad idea? Couldn’t it lead to bronze disease and irreversible damage?

The other real insight was the use of BARIUM in the creation of patinas, I’d gotten some really surprisingly high barium readings and really was flummoxed by that until reviewing this list.

I also found the use of IRON in these patina’s a little surprising. Iron does show up in my readings but as it showed up in high levels in ramo secco (Burnett, Craddock, Meeks 1986) I thought it was most likely naturally occurring. I wonder if I could spot the associated nitrate salts.

The final element that has shown up that I don’t know if it is natural or not and isn’t in this list is SILICON. In the modern world there are manufactured silicon bronze alloys but I highly doubt anyone has used these to fake coins.

Please don’t take anything in this post as ‘fact’. I’m still thinking through the material and trying to make up my mind what to think.

[begin quotation]

Patina chemicals.  The following chemicals are some of the more frequently used in patina finishes:

Ammoniumcarbonate  (NH4)2 CO3.H2O.  A mixture of ammonium bicarbonate and carbonate. Used for a bronze patina of bluish-green color.  Also called “hartshorn.”

Ammoniumchloride  (NH4Cl) A patina solution for coloring bronze a verde antique green.  Also called “sal ammoniac.”

Ammoniumsulfide  (NH4)2SO4  An excellent darkening agent for bronze and silver in highlighting during a finishing operation. The objects to be darkened are immersed in this chemical for less than ten seconds – the sulfide is the source of sulfur as the darkening agent.  Also called “sulfate of ammonia” and “sulphuret of ammonia.”

Barium sulfide  (BaSO4)  Used as a coloring agent for bronze medals for a light brown color, called “Old English.”

Copperchloride  (CuCl2)  A patina coloring chemical producing yellowish-green color on bronze.  Also called “cupric chloride.”

Coppernitrate  (CuNO3)  Used for dark blue and green patina coloring on bronze.  Also called “cupric nitrate”

Coppersulfate  (CuSO4)  Colors bronze green. It is the green corrosion on copper items in an atmosphere exposed to sulphur and moisture over long time.  The composition of incrusted patina.

Ferricnitrate  (Fe(NO3)2)  For use only by very experienced finishers; colors a dark chocolate color. Care must be used, however, as some of the nitrate salts can spot the surface.      

Liversulfide  (K2S)  Used for a bronze patina on statues and medals; it produces a color from redbrown to dark brown.  Also called “liver of sulfur,”“potassium sulfide,”  “sulfurated potash.”

Liquidsulfur.  (S)  Quickly turns bronze and silver a dull black.

Oiloflavender.  A bronze patina of pale ashen green color, formed by adding yellow pigments to oil of lavender.

Potassiumnitrate  (KNO3) is a patina solution for turning bronze a dark red color.  It is most used for tempering tool steel (heat treating dies) and for chemical analysis. It is also called “saltpeter.”

Potassiumpermanganate  (KMnO4)

[end quotation]

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