A technique I came across this past summer but have not had the chance to experiment with is mocha diffusion, a combination of chemistry and art.
The basis of mocha diffusion is the reaction that takes place when clay, an alkaline, reacts with anything acidic, such as lemon juice or apple cider vinegar. When the acidic liquid is dripped onto the surface of the slip the result is a tree or fern-like pattern.
Once finished, the slip is left to dry and continues with the normal process of firing to bisque and then being glazed with either clear or an opaque glaze.
For a brief demo of what mocha diffusion looks like watch the video on the right. For a more in-depth video I highly recommend watching Robin Hopper's video on YouTube, click here, which I was unable to embed, unfortunately.
Source: YouTube, artist's channel: glezcast, "Cerámica Moca"