Quick answer
They are spares. A set can come with blank tiles so that a lost or broken tile can be replaced by marking a blank to match it. The National Mah Jongg League's game uses 152 tiles, and blanks are not among them. Some tables add blanks as a house rule, trading a blank for any tile in the discard pile.
Open a new set and you may find a few plain tiles with nothing on them. They are not the soap, and the League's game has no use for them. Here is what blanks are for, how to tell them from the white dragon, how the house rule that puts them into play works, and what your table has to settle before it tries it.
Are blank tiles part of the game?
Not in the League's game. The National Mah Jongg League's rules use the 152 tiles of an American set, which are 108 suit tiles, 16 winds, 12 dragons, 8 flowers and 8 jokers. Blank tiles are not among them, and no line on the card calls for one.
Playing with blanks is a house rule. A table that adds them is playing its own version of the game, and the details are whatever that table agrees.
Why a set comes with blanks
A set can come with spare blank tiles in case a tile is lost or broken. You mark or paint a blank to match the missing tile, and the set is whole again. A blank used that way is no longer a blank. It is the tile it replaces, and it plays as one.
Spare blanks can also make a Chinese set playable here. A set sold as 144 tiles has no jokers, and eight blanks marked as jokers bring it to the 152 tiles of an American set.
A blank is not the soap
No. The white dragon, which American players call the soap, is one of the 152. There are four of them, they belong with dots, and the soap doubles as a zero on card lines that call for one. A spare blank is extra to the 152 and has no part in the League's game.
On some sets the soap's face is plain or lightly framed, so it can look just like a spare. If yours look alike, count out four as your white dragons before you play, and keep the spares in the box or mark them so nobody mixes them up.
How the blanks house rule works
The blanks go into the set with the other tiles, so they are dealt and drawn like any tile. A blank in your hand lets you take a tile from the discards. You put the blank down and take any tile you want from the discard pile, one for one.
That breaks one of the League's rules on purpose. Under League rules, a discard can be called only until the next player racks the tile they drew or discards, and after that it stays in the discard pile for good. A blank brings it back.
The swap is not a turn, because you neither draw nor call. The tile you take goes into your hand, and you do not have to show it unless your table agrees that you must.
What your table has to agree first
Because the League's rules have no blanks, there is no standard version of the rule, and the descriptions of it disagree. Settle these before the first deal, and again when someone new joins the table.
How many blanks go in. Descriptions of the rule suggest anywhere from two to six. Each one added makes the discard pile less final.
When a blank can be used. Some tables allow the swap only on your own turn, and others at any time.
Whether a blank can take a joker. Under League rules a discarded joker is dead and cannot be taken back. Decide whether a blank can bring one back or whether jokers in the discard pile stay dead.
Whether a tile taken with a blank can then be used to exchange for a joker in an exposed set, and whether the taken tile has to be shown.
Can you win with a blank?
Not with the blank itself. A winning hand is fourteen tiles that exactly match a line on the card, and a blank appears on no line. A blank still in your rack does nothing for your hand, so it has to leave your hand before you can declare mahjong.
The tile a blank brings back is a different matter. It is a real tile, so it counts anywhere that tile can go. A joker can never be part of a pair or a single, but a tile taken with a blank can complete a pair, a single or a Singles and Pairs hand.
How blanks change your defense
Under League rules the discard pile is a record you can count on. A tile in it is out of the game, so counting the copies already thrown tells you how many are left for anyone to use. Our guide to what not to discard builds on that count.
With blanks in play that count is no longer final. Any tile in the discard pile can return to a player who holds a blank. Keep track of how many blanks have been spent, because each one still in play is a discard that can come back.
For your own hand, holding a blank keeps it for the tile you need most. Spent early, it may take a tile you would have drawn anyway. Held, it can fetch the last tile you need, as long as a copy is sitting in the discard pile.
Put it into practice
Reading about it is one thing. Have the coach read a real dealt hand for you, free. It names the direction the hand goes for, what to keep, what to pass, and the reasoning behind each call.
Want the coach on call? The Club adds the coach for your own tiles and for each morning's hand, all 10 lessons, and every new NMJL card taught the week it lands, for $14.99 a month, cancel anytime. See what the Club includes
Our free read, drills and practice table have no blank tiles. Deal yourself a hand and put it into the free read. Mei, our AI coach, reads it tile by tile, says which direction it goes for and which tiles do nothing for it, and explains why.