you are exited
The expression is usually, "You could have knocked me over with a feather!" It means, I was so surprised (and distracted or disabled) that I could have been easily knocked over with a feather. In other words, my defenses were way down, or non-existant so almost anything could have knocked me down.
The phrase "you could have knocked me over with a feather" means that you were very surprised. A person who is so surprised that they are a bit disoriented might feel like something as light as a feather could be enough to knock them over.
A homograph for a duck feather could be "quack," as it can refer to the sound a duck makes or to a type of medical professional.
It could mean that you have ovarian cysts or cancer. Or it could mean that you were ready to start your period, and it knocked things loose.
If by "after time" you mean once the diamond is on your hand, the only way that a feather can be formed is if there is a catalyst to the occurrence ... by this I mean, for example, if a diamond was hit or damaged it could act as a catalyst to an interior feather spreading inside of the stone.
Possibly, other culprits could be wild dogs, cats, raccoons, juvenile delilnquents and last but not least, the weather.
Maybe it's not air, it could be an ingrown feather or it could be a tumour?
The term "plucking a finch" is an outdated term referring to sex. Your passage really needs to be considered with the context to be sure but, plucking a finch to leave no feather could mean that the person has sex with a lot of people.
"feather in the wind" - can you say that in English? And what does it mean?
It would mean that you put a feather into a cup. Perhaps you mean "a feather in your cap," which was a way of showing an achievement and has come to mean any achievement.
Sending a black feather can mean a great many things. Sometimes sending someone a black feather can mean wishing death on them.