Sextic surfacesWritten by Paul Bourke
Sextic equations are in general equations of a variable with power terms up to degree 6.
In 3 dimensions the equation contains all the possible terms in xn, yn, zn. In other words the sum over all the terms of the type shown below where m + n + o <= 6, there are 84 possible combinations so there are that many constants ci.
Example by Edmond Bonon, rendered in PovRay [sextic.inc]