Soap: The Tile That Does Two Jobs
The white dragon is a dragon, and it is also a zero. Those are two different tiles that happen to share a face.
Nothing on the card confuses people as reliably as soap. Not because either of its jobs is hard, but because nobody tells you there are two, so you learn one and then meet a line where it makes no sense.
As a dragon
There are three dragons and each belongs to a suit. Red with craks, green with bams, white with dots. Soap is the white one, so soap is the dot suit's dragon.
In this role soap behaves like any other tile. In a pung, kong, quint or sextet it takes a joker. In a pair or a single it does not — the grouping decides that, never the tile.
Everywhere else on the card, colours tell you how many different suits a hand needs and never which ones. Tiles sharing a colour share a suit; different colours mean different suits, and you choose which. Dragons are the single place a colour points at a particular suit — which is exactly why they are worth learning separately.
As a zero
Now the other job. Some lines print a 0, usually inside a year, and the tile you put there is a soap.
A zero is suitless. It belongs to no suit, which has one consequence people miss: the League may print a 0 in any colour, and that colour is meaningless. Read a suit out of it and you are reading a signal that was never sent.
The limit matters as much as the rule. Soap is a zero only where the card actually prints a 0. It is not a zero you can drop into a hand that wants one, and it is not a ten. The official rulebook has said so explicitly since 2018.
Which job is it doing?
Look at the line, not the tile. If the card prints a dragon, it is a dragon. If the card prints a 0, it is a zero. There is no situation where you have to choose.
| The card prints… | Soap is… | Takes a joker? |
|---|---|---|
| A dragon in the hand’s colour | The dot dragon — so the hand is in dots | In a pung or larger, yes |
| A dragon in a different colour | An opposite dragon — so not the dot dragon | In a pung or larger, yes |
| A 0 | A zero, with no suit | Only inside a pung or larger — which depends on the grouping, not on the number printed |
That last row catches people. A 0 inside a year — 2026 — is a single tile, and a single never takes a joker. The zero is not special there; being a single is what does it.
The white dragon is a plain tile with a rectangle on it, and it looks like a bar of soap. The nickname is universal at American tables and you will hear it far more often than "white dragon". Both are correct.
The mistake this prevents
A player holding soap sees a line with a 0 in it and reasons: soap goes with dots, the 0 is printed in the same colour as the dots on this line, so this hand must be a dot hand. Every step of that is wrong. The zero has no suit, so its colour said nothing, and soap was standing in as a digit rather than as a dragon.
When you have read it all: the rules workbook, 105 questions with an answer key that cites the rule behind every answer, $19.
Where this comes from
The dragon-suit pairings are printed on the back of the National Mah Jongg League's card and are confirmed independently by Tom Sloper's rules FAQ and by I Love Mahj. That a zero is suitless, that soap is a 0 only where the card prints one, and that the 2018 rulebook states this explicitly all come from Sloper's FAQ, which cites the League's own rulebook.
No hands, values or card arrangement are reproduced here. You need your own current card.