Glycerine rivers

Translucent crackled veins running through the cut face, most visible in a colored bar.

Crackled lines through the bar

A pattern like crazed glass or a dry riverbed, in a lighter or more translucent shade than the surrounding soap.

Structurally the bar is fine. This is purely appearance.

What they are

Areas where the soap gelled differently, leaving a different crystal structure and a different translucency.

They are called glycerine rivers by convention rather than by chemistry: glycerine is present throughout, not concentrated in the veins.

What causes them

Overheating during gel, which is the main one.

A water discount, which concentrates everything and makes the effect more pronounced.

Titanium dioxide specifically, which is strongly associated with them and which many makers use for white and pastel bars.

A high gel temperature generally.

Whether to fight them

Some makers do it deliberately. In a rustic or marbled bar they read as character.

In a crisp geometric design they read as a fault, and the customer cannot tell the difference between intentional and not.

To avoid them: soap cooler, do not insulate, use less titanium dioxide, and consider preventing gel entirely.

To get them: the opposite.

What matters commercially is consistency, because a range where some bars have them and some do not looks like a process that is not in control, which it is.

References