Hmm, what can I blog about.

You know what I learnt about on Thursday at Uni? I started learning how to do thin section analyses of pottery. Mark told me off when I mentioned it since I kept referring to "stuff" instead of using proper descriptions. Okay, so I can see how a narrative with a lot of different things all called "stuff" might not be much use! So I'll try and be more specific. But it might not be all that interesting. It's just the most interesting thing that I've done lately. :)

The point of thin sectioning pottery (this is archaeology, in case you were wondering) is to get a really thin... section of pottery... and look at it underneath a microscope. Then you can see what mineral inclusions are in the pottery, and count what percentage of the pottery is made up of the aforementioned inclusions. Clever, eh? The minerals are either things that occur naturally in the clay, which may help figure out where the clay came from, or are added as opening materials.

I suppose I should explain what opening materials are. (This is why I ended up calling everything "stuff", so I didn't have to explain everything!) Potters add opening materials to clay so that when it's fired the pot doesn't explode. You see, the pots are never completely dry, so when the water evaporates it forces its way out and the pot breaks. If you've put minerals in there, it gives the water a way to escape without exploding the pot. The minerals hold the clay together! The whole exploding pot thing is a bigger problem if you're firing the pots in a bonfire. (Hence Prehistoric pottery has lots more mineral inclusions, on the whole.)

I'm generalising, but you get the idea.

So, if you have a pot and you want to find out more about it, working out what was put in the clay is really helpful. I mean, you can group pots together on the basis of what they're made of (their "fabric"), and you can (sometimes) work out where the pots originated. Since Prehistoric pottery all looks pretty much the same (at least in the UK!) using their fabrics can help. But it's useful for pots of all ages. :D

I think that's all the background needed, so I'll tell you what I learnt on Thursday! It was all lab work, which was peculiar for me, since I haven't done "science" since I did my GCSE's... The labs are all packed full of boxes of things, old equipment, things that look like they might be rubbish. They're crowded. In two of the labs we worked in it was hard to get across the floor - you had to go around the heaps of junk. Somehow I never think science should look so messy!

First of all we had to choose two bits of pottery to work with. Then we had to use a circular saw to cut a section out of the pottery. I wasn't completely happy with the idea of getting close to a carbide tipped saw, but it wasn't as bad as I thought it was going to be! I managed to saw off my vaguely rectangular sections of pot without cutting off my fingers. Although as the lecturer pointed out, the saw wouldn't cut off your fingers, it'd grind them off. (Nice.)

The next stage in the process is to polish the top surface. This is done with a substance that looks like dark grey sand. You mustn't inhale it. That would be bad. You put some on a sheet of glass and water, so you get a sort of paste. Then you put the surface you want to polish on it and start moving the pottery around in little figure of eight motions. After a while you take it off and rinse it and... it's all smooth! Wow. :)

Now your pottery is nice and smooth on one side, you have to grind it until it's 30 microns deep (hence "thin section"!). Before you can do that, you have to seal it so that it doesn't fall apart. This is done with the aid of a handy vacuum pump and a bit of Araldite. (Highly scientific!).

You put the Araldite in a plastic tub and pop it into the vacuum chamber. Then you create a vacuum three times, bringing the chamber back to atmospheric pressure after creating the vacuum (and thus getting rid of bubbles in the Araldite). The whole vacuum process is made more exciting by having ancient broken equipment. The valve on the chamber doesn't work, so the perishing rubber tube that leads to it has to be clamped with a metal clamp that tries to jump off whenever it gets the chance.

Once you've debubbled the Araldite you add the pottery to it, polished side down. Then you put the tub back in the vacuum chamber and create a vacuum three more times. This should draw the Araldite into the pot, occupying the spaces that used to be filled by air! And thus the pottery should end up completely soaked in the substance that'll stop it disintegrating. The pottery's turned polished side up and put in a dish in the drying oven. And that's as far as we got on Thursday.

I'm not looking forward to the grinding part - it sounds hard. Even for people who know what they're doing! You have to grind it until the minerals change colour. Yikes!

That was archaeology thin sectioning part 1, then! :)

posted by Fiery Fred @ 8:50 PM