All my preliminary samples are ready for analysis, and getting them ready has been pretty complicated. So here’s a flowchart I made/procrastinated.
The samples are a few different things. I have whole coins, scrappy fragments of coins, silver artefacts (from the Batavia), chunks of concretion that came off the coins and drillings from silver bullion (from the Senora de Atocha).
First of all I photographed everything. In archaeology in particular, when in doubt, take a photo! Because the next thing you’re likely to do is disturb or destroy whatever it is, so best to have a photo just in case.
Then I started preparing different things for different types of analysis.
I spot cleaned the whole coins with alumina in suspension, and wiped off the alumina with a tissue dampened with acetone, just to get the top gunge off. Then I circled the area I had cleaned, because when they’re in the laser, it’s pretty difficult to see the bit you prepared.
I very carefully clipped teeny tiny pieces off the scrappy coins and the artefacts (these artefacts are not display quality, in case you’re having a heart attack, as I almost did when it was suggested that I would be clipping up artefacts)
I mounted half of the scrappy coins, the bullion drillings and the artefact clippings, as well as 3 chunks of concretion in resin. (Hot tip – in the event that you’re not sure how to mix resin; rather than watch YouTube videos of little old ladies doing craft projects with resin, just call the number on the tin, they will tell you how to do it). After they had set overnight, they were nicely covered in vaseline, so they got cleaned in an ultrasonic bath, which is also how your jewellery gets so shiny clean after it’s been to the jewellers (coincidentally, all the jewellery I was wearing “fell into” the ultrasonic bath that day. Weird.)
The rest of the scrappy coins, bullion drillings and artefact clippings got dissolved in acid (to be honest, I can’t help but feel a bit queasy when I think that I dissolved archaeological artefacts in acid, but, all in the name of science! What we learn from these things will hopefully make up for it).
So now, all the whole coins and half of the mounted things will be analysed using LA-ICP-MS, laser ablation inductively coupled plasma mass spectrometry, to non-destructively look at trace elements.
The other half of the mounted things will be etched, to look at the crystal structure of the minerals.
The dissolved things will be analysed using solution-ICP-MS, to look at the trace elements.