Mold is a period-4 oscillator found by Achim Flammenkamp in 1988, but not widely known until Dean Hickerson rediscovered it (and named it) in August 1989. In terms of its minimum population of 12 it ties with mazing as the smallest period-4 oscillator, but in terms of its 6×6 bounding box it wins outright. In fact, of all oscillators that fit in a 6×7 box it is the only one with period greater than 2.
It emits dot sparks, which can support other patterns such as four molds hassling eight blocks, traffic circle and "butter".
Mold is the twelfth most common naturally-occurring oscillator in Achim Flammenkamp's census, being less common than the spark coil but more common than the quadpole on ship. On Catagolue, it is the most common period 4 oscillator, being more common than mazing.
The first natural mold stator variant, cis-mold on dock, occurred in May 2015.
- 12P4.1 at Heinrich Koenig's Game of Life Object Catalogs