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Pattern type Spark
Number of cells 2
Bounding box 2 × 1
Discovered by John Conway
Year of discovery 1969

A domino is two cells connected orthogonally, and it is the only possible 2-cell polyomino. It almost exclusively appears as a spark, in which case it is referred to as a domino spark. A domino-shaped rotor is known as orthogonal on-off.

Domino sparks are arguably the most common type of spark of all, as they arise as the last living state of larger sparks such as the banana spark (and therefore cavity), V spark (and therefore the phi spark and line-of-six spark).

Production of dominoes as sparks

Domino sparks can either be produced parallel or perpendicular to an oscillator's bounding box. In order to be considered a true domino sparker, the spark cannot be a descendant of a higher spark in the same place such as a V spark.

Parallel sparkers

Parallel domino sparkers are the most common type of domino sparker. The heavyweight spaceship is a small spaceship which produces domino belly sparks, which can pose useful for deleting many small objects produced by puffers such as blinkers, blocks and gliders, as well as perturbing larger reactions. The "heavyweight" namesake is carried on to the stationary oscillators heavyweight emulator and heavyweight volcano, which produce domino sparks in much the same way at periods 4 and 5, respectively.

Other important domino sparkers include the pentadecathlon and Merzenich's p31. The fumarole also produces a domino which is usable for perturbation, however the existence of the domino is integral to the oscillator's continued evolution and as such must be used more carefully than more distant sparkers like those mentioned previously.

Perpendicular sparkers

Main article: Pipsquirter

Oscillators which provide domino sparks oriented perpendicularly to the bounding box are referred to as pipsquirters and are documented on a separate page.

Use in oscillators

There exist two wicks which can be constructed solely from disjoint dominoes. A diagonal spacing of dominoes will consist of dominoes in all phases, whereas a more knightwise arrangement will be composed of sparse dots in every other generation. Both wicks can be stabilised by period-2 components.

x = 35, y = 23, rule = B3/S23 31b3o2$30bo2b2o2$8b2o2bo15b2obo2bo$8bobobo19bo$12bo14b2o3bo$10bo$10bo 15b2o$8bo$8bo16b2o$6bo$6bo17b2o$4bo$4bo18b2o$2bo$2bo19b2o$o19bo$obobo 16bobo$o2b2o13b2obob3o$21bo4bo$19bobob3o$20b2obo! #C [[ THUMBSIZE 2 THEME 6 GRID GRIDMAJOR 0 SUPPRESS THUMBLAUNCH ]] #C [[ ZOOM 10 GPS 4 AUTOSTART ]]
Two possible period-2 wicks composed entirely of dominoes
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RLE: here Plaintext: here

The squaredance agar is entirely comprised of dominoes in all phases.

In other rules

In Just Friends (B2-a/S12) and similar S1e rules, the domino is a still life.

In Logic Rule (B2ae/S) and similar B2a rules, the domino is a linear replicator whose behaviour follows that of Rule 90.

See also