We are currently testing small prehistoric sites. For control, we are excavating in 5cm arbitrary levels within natural stratigraphy. To check for small pressure flakes that would be missed with standard screening, soil samples are taken from each level and water screened through window mesh. To break down clay and speed the process we borrowed a trick. Soil + Baking Soda + Water = Deflockulation (so we are told it is called). Whatever it is, it works like a charm. Give it a few minutes to a few days, depending on how dense the clay is, then stir to make slurry. deflock