The second pour
Updated
An extra step that separates a hand-poured tube that looks professional from one that does not.
Why there is one
Balm shrinks as it sets and the last liquid is in the middle, so a single pour leaves a dimple, and sometimes a channel running down inside the stick.
The second pour fills it. It is standard practice rather than a remedy for a fault.
Timing it
Wait until the surface has set and the depression has formed, but not until the stick is cold through.
Too early and the second pour merges with liquid underneath and dimples again. Too late and it sits as a separate disc that can lift off in use, the customer gets a small wafer of balm on their lip and concludes something is wrong.
The window is minutes and it is specific to your formula and your room. Find it once, write it down.
Holding the reserve
Keep a small amount of the same melt at pour temperature, covered.
Covered matters: an open reserve loses flavor and skins over. And at temperature rather than reheated, because reheating the reserve makes the topped portion a slightly different product from the body of the stick, which can show as a visible line.
When to skip it
Pots and jars do not need it. A flat surface with nowhere to sink shows a faint depression at worst.
And a formula with very little shrinkage may not need it, which you discover by pouring a test row and looking. Do not do the extra step out of habit if your product does not require it.