The important factor present in the creation of pottery pieces might vary depending on the specific context or artistic intent. However, if we consider the general trend in contemporary pottery, "experimentation with form that was not standard" and "experimentation with color and design" are often key factors that influence creativity and innovation in the field. Artists frequently explore new shapes, textures, and color combinations to push the boundaries of traditional pottery and express their individuality.
If the pottery pieces in question were created with a focus on traditional techniques and styles, then "standard usage of materials and design" or "standard usage of color and form" might be more relevant.
Ultimately, it depends on the specific characteristics of the pottery pieces being analyzed. Which of these two aspects resonates more with the pieces you have in mind?