This Photoshop technique uses Layer Styles and brushes to form a cracking effect down the side of a teacup
In Photoshop, set up the Brush tool by selecting the Square brushes from within the Brushes palette, setting size to 4px.
On a new layer, painting straight lines by holding Shift while clicking erratically, create the cracked pattern.
Open Layer Styles by double-clicking on the layer. Add the Bevel & Emboss style with Technique set to Chisel Hard.
Also add the Color Overlay style, picking a colour from the contents of the teacup, in this case the blue sea. This fills is the gap so it looks more realistic!
Whenever you paint on this layer, the Layer Styles are automatically applied!