Carstens  Tönnieshof was one of the few companies that used brown clay.  The colour of the clay varies from very dark brown to warm, red brown. Pieces with a light brown clay occur but are very rare.

Carstens Tönnieshof used a two to four digits long form number followed by the size in cm. Very early forms used the numbers 1, 2 and 3 for the size where 1 was the smallest size. Early forms can be without form number. Also some forms in the Atelier and the Töpferei series were without form numbers.

Some form series have a letter in the form number.

A: Was used for the Alaska series made for Goldscheider. (1960)
B: Was used for some pieces in the Boutique series. (1967-early 70s)
C: Was used for some early pieces in the Carstens Atelier series. (1962-?)
E: Was used in some pieces in the Europa series. (1967-?)
M: Was used for the Manilla series. (1967-1968)
R: Probably represent relief decors (Rillendekor). (early 50s)
T: Unknown. (early 50s)