Xeramtheum: I think the bread knife could work in some limited cases, but here in the Southeast archeologists use a plain round nose Razorback shovel and cut the tip straight across at about 10 cm. This slight dip that gives you the power to scoop out shovelful after shovelful. With the sharpened razor sharp edge you can shovel-skim a flat surface or dig 4 x 4 m square holes hour after hour day after day--building A Schwarzenegger legs. The razor sharp edge makes it easy to punch out a straight edge. Any bumps are smoothed out with a sharpened flat mason's trowel. These two tools, along with a bastard file to sharpen tool edges, will save your back, and allow you to cut a box-shaped excavation with precision edges even in clay soil.

in clay soil, we wet it down the night before and cover with black plastic. The next day its ready to dig.

When I worked at the Museum at University of Florida in Vertebrate Paleontology we used something similar on digs .. they are great if you aren't little a little old lady with benign positional vertigo like me. I have to be very careful about bobbing my head up and down. I pretty much have to sit down on the ground to do any gardening now.

xeramtheium. I am also a little old lady (73 this year) with positional vertigo! We all work with in our limitations and knowledge! Thanks for the article. I forgot to say, we laid our squares with string attached to survey pins (these are 12 in long screw eyes). This gives a straight line to guide cutting the shovel trenches.