Some recipes have a element aspect which is listed in the lower part of the crafting log window.
It's common for vintage stuff to have such a special elemental aspect.

The difference is that your progress is much higher if you use the brand skill with the right element while the normal synthesis actions effectiveness is lowered.
Flawless Synthesis might be ok for low levels but 40 progress is not even half of what you want to see on higher level synths.