Using Cu K-Alpha/K-Beta ratios to determine plating

[Kirsten Travers Moffitt]

Hello, 

We are trying to confirm the presence of gold plating on an object using Cu K-alpha/K-beta ratios (If anyone has a better method, I would love to know), but we've hit a snag. 

We analyzed three references containing copper, and all had ratios of 7.3 : 1 

A sterling silver reference was 5.94 : 1

Our unknown gold-plated (?) object was 6.22 : 1

Why is the sterling silver reference, definitely not plated, so low in comparison? 

What does this mean for the unknown? Our conservator has examined it and is absolutely confident it is plated. 

Spectra below (Red: unknown; Green: CHARM bronze reference; Pink: Brass reference; Blue: Pure Copper Reference; Dark Blue: Sterling Ag reference). All were collected with a Tracer 5g using the Alloys2 calibration. 

Thoughts? Thank you in advance!

Kirsten Moffitt

[Aaron Shugar]

Hi Kirsten,

So to answer your question about the sterling.  You will get variable Cu ratios based on how sterling is processed.  It is an alloy of Ag and Cu, but the Cu at the surface is oxidized and then etched out - typically followed by burnishing the remaining silver. As the silver gets polished, the Cu ratio will change. I had a student work on this several years ago.  

So depending on the thickness of the enriched silver, your Cu ratios may be lower.

Are you planning on trying to measure the gilding thickness by looking at the attenuation?

Aaron

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[Kirsten Travers]

Thanks Aaron! Yes we would like to calculate the thickness of the gold plating, but do not know how. Can you help?

Kirsten

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