Milling

Milling is what I'm going to be doing quite a lot of over the next year. Its the cutting out and collecting of each sample from the stalagmite ready for analysis in the mass spec.

 

This is the mill. A super-accurate (0.01mm) computer controlled drill. We have two, this is the compact shiny new one which I have set up and am learning how to use. The other is a big bulky thing that we've been using for years.  The old one is good, but it doesn't have good z-control (up/down).

 

You start by lining up the stalagmite very carefully and clamping it in place. You need to be able to transect across the area you want using just one axis, so the line needs to be perfectly aligned. Then you mill a trench in the material to get rid of surface contaminants and any carbon from the pencil marks on the stal surface.

Now you're ready to go.  By milling in a mm deeper than the trench and slowly inching your way along you slowly cut out a small piece of the stal into a fine powder. Then you collect all the material on a small scalpel and transfer to a vial. Sounds easy, but its really fiddly. Then you clear the cutting area of any loose debris with compressed air so as not to contaminate the next sample, then move on. Repeat, repeat, repeat. Several hundred times! And so on and so on until you've finished your PhD!