Responding to Blackwood with a Void
Yikes! I can't believe this article ever made it to my site. This is a pet peeve topic for me. I always get asked about it. The problem is (and please don't take this the wrong way) that 99% of the people who ask, should not bother worrying about it.
a) It rarely comes up
b) Even if it does come up, it is needed only for reaching 7 (when just getting to 6 will usually be a good enough result)
c) When it comes up once every 3 years, who can possibly remember the agreement?
d) There are many different ways to show the void
e) It can get quite complicated--and could depend on what is trump (much easier with spades; near impossible with clubs).
f) You would need to have a regular partner who studies and agrees on the same methods. This is not for casual partnerships.
All of those reasons make this topic completely flunk my: "Is it a convention you should worry about" test. Only if you are a professional or long-term experienced partnership, is this worth delving into.
I finally came up with a good reason to put this on my website. From now on, when faced with the question, I can just say: "Look it up on my website." I refuse to dictate to a student lines and lines of code to memorize. I can't think of anything more impractical. But, if you asked me, and I said, "see the site" -- here you are.
So, now, if you wish to waste hours of study and thousands of braincells on an unimportant topic, I refer you to 3 good sources as below. All of these have merit, and are basically similar in approach. These are methods you can rely on (as opposed to some incoherent mumbo-jumbo you might find elsewhere on the internet). With luck, at least some of these links will work when you click them.
1) Methods from bridgebum site
2) Methods from pattayabridge site
3) Martel-Stansby method
Or, you can make me happy and not click any of these links and worry about other bridge topics/methods which are infinitely more important.