It does look like a small hairline crack to me, but it't kinda hard to tell.
What I would do (I know you already put NP over it but for anyone else reading the thread) clean the egg with rubbing alcohol, put a very thin coat of natural nail polish over the crack area (colors work too, as long as they're natural), and make sure that the incubator is extremely clean (sterilize it before setting any eggs no matter what).
One other question, can you set two eggs, and if both hatch, raise them together, integrate them together, and then later on give the extra duckling to your friend?
They really need another duck to grow up with. Trust me, I've tried to raise lone chicks. Who wouldn't love an imprinted, super friendly fuzz butt? But it just can't work. Even if you can give them all the attention in the world they'll still be unhappy. When you go to integrate a single bird, he'll be rejected and attacked. He will NEVER be fully accepted. It's incredibly heartbreaking. If you can just raise two until they're established in the flock, you'll have no problems at all. And they'll still be very friendly if you hand raise them. They just need the companionship of another like them. They crave it.
It should be really easy to sell the extra on Cl or something like that. Especially if it's young enough that you don't know the gender yet. If there's a chance it could be a female people will snatch it right up. Or could you sell one of your current ducks to make room for two new babies? Maybe an extra drake?
There's also a chance that one of them will die and you'll be left with just one anyway. You never know.
I hope you'll share some adorable pictures with us
Aww..
