Bridge & other card games/void showing
in blackwood how to show void in a suit
One method is as follows
Bid 5NT to show 2 aces plus a void
Bid 6X to show 1 ace plus a void in suit X when X is below the trump suit
Bid 6 of the trump suit to show 1 ace plus a void in a suit above the trump suit.
Playing Roman Key Card Blackwood the responses are the same except showing keycards instead of aces.
Not everyone favors this approach as in some cases bidding to the 6 level with just one ace (keycard) and a void might be too high. Another approach is as follows
5NT shows 2 aces or keycards and a void
6C shows 3 and a void
6D shows 4 keycards and a void (it is impossible to hold 4 aces and a void).