comma indicating afterthought: bought a new pitcher, with a strange

Are these sentence correct:
(The phrases after the comma are supposed to be after-thoughts. That's why there are commas.)

1-I read his new book, about Darwin's theory of natural selection.
(Meaning: I read his new book, which is about Darwin's theory of natural selection.)
[I think here the comma is necessary. If it is taken out, the sentence will imply that he has written at least one other book about natural selection. With the comma there is no such implication. We don't know if he has written any other book about natural selection.]

2-I bought a new pitcher, with a very strange handle.
(Meaning: I bought a new pitcher, which has a very strange handle.)

3-He has made a few feature films and a documentary, about Gypsy music.
(Meaning: He has made a few feature films and a documentary, which is about Gypsy music.)

I am trying to figure out in what cases one can take out 'which is' or 'which has'. I actually don't think that these sentences work and would always put in 'which is' or 'which' has in writing. I am not sure that they are wrong though and I think they might be used in spoken English. In 2 and 3 we would have correct sentences if we drop the comma. That I know. I wanted to see if they'd work with a comma, ie. if the 'clause' is non-restrictive.

All three sentences are correct without the which is/has, but you should remove the commas. The concept of using a comma to indicate an afterthought is novel, but it has no basis in grammatical rules. Strictly speaking, you shouldn't have "afterthoughts" in the middle of a sentence -- you should do the thinking before you start the sentence.

1-I read his new book, about Darwin's theory of natural selection.
There are two different sentence possibilities.
I read his new book about Darwin's theory of natural selection.
As you said, this implies that he has written at least one other book on this topic.
I read his new book, which is about Darwin's theory of natural selection.
The relative clause gives us additional information about this book, only.
I suppose you could omit which is, but I wouldn't.

2-I bought a new pitcher, with a very strange handle.
This sentence does not need the comma.
I bought a new pitcher with a very strange handle.
You might write it with which is, but it sounds really artificial.

3-He has made a few feature films and a documentary, about Gypsy music.
(Meaning: He has made a few feature films and a documentary, which is about Gypsy music.)
This sentence, too, is better without the comma, and odd with which is.
He has made a few feature films and a documentary about Gypsy music.
With the comma, the sentence suggests to me that all his films and the documentary are about Gypsy music.