Geometric effects on surface roughness in precipitation

We investigate the branching of an advancing precipitation front to a nonplanar shape as the solute concentration in a supersaturated solution is increased beyond its critical value. We aim to learn whether new branches can be detected by measuring the speed of the front. We present a condition that determines whether a cross section of arbitrary shape will lead to a pitchfork or to a transcritical branching. Both are possible. Rectangles and circles imply pitchfork bifurcations, equilateral triangles and hexagons imply transcritical bifurcations.