material: acrylic Vero black
technique: 3D print, polyjet matrix-technology
dimensions: approx. 15 x 15 x 15 cm.
The Accretor software is developed to explore the diversity of shapes that can arise from a virtual process of accretion: depositing
particles onto a small clump. Starting with this tiny "seed", complex forms can emerge by the repeated addition of matter according to a set of
rules. These rules encode whether or not a particle will be deposited somewhere on the surface, depending on the spatial arrangement of already
existing particles at the deposition site. Each set of rules leads to a characteristic growth, a unique development of a shape in time.
The accretion process takes place in an imaginary 3-dimensional space, a grid of cubic cells. The particles are the smallest units of this space:
tiny cubes, also known as voxels (volume elements). The cells in this space are either empty or filled. All the filled cells together make up the
object that grows. A particle may only be deposited onto the surface of an existing object, in other words, it may only fill an empty cell that is
next to a filled cell. This constraint ensures that the growing "body" remains one piece, and there will never be "floating" cells that are not
connected to the rest of the body.
Imagine the simplest case: a single cubic particle in an otherwise empty space. This cube has 6 neighbouring empty cells around it, each of which are
in contact with one of the cube's faces, and thus could be potential accretion sites for the next particle, ensuring connectivity. Furthermore, this
cube has 12 neighbouring cells that are in contact with the cube's edges, plus 8 neighbouring cells that are in contact with the cube's corners. All
in all, a cubic cell in the grid has 26 immediate neighbour cells, and the state of all these cells (empty or filled) plays a role in the accretion
process around that cell. There are many possible states of a cell and its immediate environment. For instance, given a centre cell that can be either
empty or filled, surrounded by 26 neighbour cells, which also can either be empty or filled, the number of possible states is 2^27 = 134217728.
A set of rules is generated, one rule for every possible cell environment state. Each rule specifies whether a particle will deposit on the surface
and the combination of all the rules determines the entire process of accretion. There is no randomness involved in the growth of an object, the
rules are strictly obeyed. But the rules themselves are generated randomly before the accretion process begins. The number of different rule sets to
specify the accretion process is huge. In the example above, there are 2^134217728 possible rule sets.
Many of the rule sets, however different, will result in octahedroid, spheroid and cuboid shapes. Beside this, many growths die at an early stage.
There are, however, types of shapes that are much more complex. These shapes exhibit slow growth, where the accretions happen in a delicate feedback
loop with the past stages of the form, and where global effects arise that are almost impossible to deduce from the local particle interactions.
These artificial rarities are the most intriguing because they often resemble naturally grown objects.
Read more in this article of Mitchell Whitelaw, published by MIT Press in the journal Artificial Life: