Mocha Diffusion, also know as Dendritic Slip, is a technique that dates back at least 200 years. This technique creates branching patterns on the surface of pottery, and resembles dendritic patterns often found in nature - in lightning, in veins and the neurons in our brains, in rocks such as dendritic agate and dendritic limestone, and branching patterns in beach sand where waves run back into the ocean.
Mocha diffusion is named after a type of stone called a Mocha Stone, a type of moss-agate originating from Mehka, a port city in Yemen which was called Mocha by the English in the 18th century. This technique was originally used on English production slipware pottery in the 18th century, but due to those pots being made of low-fire red clay which wasn’t particularly durable not many examples remain. The theory is that this technique was discovered when potters in the 18th century noticed these branching patterns when they spit chewing tobacco into wet clay slip, gross, I know.
When looking into recipes and formulas for this technique, not much information is available, but you will come across some bizarre ingredients not normally used in the making of pottery. I’ve heard claims that this technique traditionally used tobacco, and more recently people use vinegar (especially apple cider vinegar), wine, soy sauce, and nail polish remover. These unusual ingredients can distract from the more important consideration, why does this happen?
The claim is that it is a difference in pH between an acidic colorant wash and a naturally Alkaline clay slip. Uhm, I'm just gonna say I don't believe this, or at least, I don't think pH is very relevant, if at all relevant. I've been writing an "article", which has now gotten too long and extensive to be an article but still too short to be a book, about my alternative theory of how and why this technique works, backed up by technical info from scientific articles about fluid dynamics, and hopefully backed up by beautiful results of putting that theory into practice.
Hopefully this article will be done soon, it'll be a how to with simple and advanced experiments with Mocha Diffusion, and detailed descriptions of how to get these patterns and how to get great results with this technique, problem solving, and some of my currently proprietary formulas. It's been a work in process for a long time as I want it to be very thorough, and a useful reference for myself as well as other potters.