Shell tempered ware
Two of the fragments I dug up last week were shell tempered ware. The potter had crushed shells into the clay which produces a stronger pot after firing. This temper provides archaeologists with a great way of differentiating between pottery styles.
In acidic soils lime tempers are washed out of the clay leaving honeycomb holes. However, from the Wraysbury site, the potsherds are coming up with the white flecks of shell still in situ.