Antoinette Badenhorst explains the bullshead wedging technique in her online workshop Understanding Porcelain.
Wedging clay is a hot topic to discuss among potters. Some believe that spiral wedging is the best way for preparing the clay, while others will not even think about moving away from the bull's head or ram's head wedging technique. Some ceramic artists even differ about the spelling of the wedging technique - is it bullshead, or maybe bull's head or even just bulls head - and the same argument is used for the ramshead method. Then we also have other techniques like slam wedging and there may be more, but we will discuss that later.
Some ceramic scholars learn that a chunk or block of clay is cut into two pieces with the shape of a wedge. The top one is lifted from the lower one, turned over and slammed onto the wedge that remained on the wedging table. This process is repeated until there are no more air pockets in the clay. The wedging process helps to get the clay uniform in plasticity, texture and color. Roughly 20 wedging's or kneading is enough to prepare the clay.
How to do spiral wedging (David Voorhees)
How to center clay on the pottery wheel (Antoinette Badenhorst)
Demonstrations, tips & techniques
E-course (online workshops)