How to do Mocha Diffusion on pottery + tests
Mocha diffusion is a visually appealing, easy, and great way to decorate your ceramic work. The word Mocha originates from the port city of Mocha in Yemen, where moss agate (also known as mocha stone) was traded. Long story short, it looks like a cool rock we once traded. While the pottery community is relatively small the mocha diffusion community within it is even smaller. Which leads to a small amount of misinformation about how it’s done as pseudo science and speculation is circulated between a small few who have truly figured it out. In this blog not only as I going to teach you how to do Mocha Diffusion but I am also going to dispel much of the misinformation about how it’s done. But first, lets get a base line of what mocha diffusion is for anyone who is unfamiliar.
This is a video I have made for youtube about mocha diffusion. While the name mocha diffusion was adopted to the technique from the agate rock once traded, this is actually a hydro phenomenon called viscus fingering. Viscous fingering is a phenomenon where a less viscous fluid pushes a more viscous fluid during interaction, creating finger-like patterns at the interface between the two fluids. This instability arises when a fluid with lower viscosity (like water) displaces a fluid with higher viscosity (like glue or oil). In the ceramic and pottery world our main high viscosity (what I call standard) substance is slip; which is essentially watered down clay. This watered down clay, AKA slip, has relatively higher viscosity than most things we use in the pottery world. We can suspend color/ oxides in such as water, milk, lemon juice, tea, bleach, I even used mouth wash at one point just because I could. Luckily for us we have an abundance of low viscosity things around the house in comparison to our slip standard that can easily create viscus fingering. This means things such as colored oxides, mason stains, and almost anything that won’t burn off in the kiln can be added to the water as a colorant. This results in the cool color you see most artists use to keep their color after firing. They are using red iron oxide, cobalt oxide, black iron oxide, dark colorants that they know will survive the firing process. Things like food coloring, while visually appealing before the firing, will burn off in the kiln and result in loss of color after the firing.
While viscus fingering works just fine, we can help the low viscosity fluid travel along / push the high standard by adding a sufactant; A substances that reduces surface tension in liquids, increasing their wetting and spreading properties. Surfactants are agents that have both a hydrophobic (hates water) and a hydrophilic ( loves water) end in the same chain which makes things that would not interact with water do so. Luckily for us we have a very popular surfactant in most homes in the form of liquid soap. This in turn helps reduce the surface tension between the high and low viscosity interaction and enhances the viscus fingering acion. It makes what already worked work better!
It truly is a very easy process to figure out. At most you might have to play around with the vescocity of your standard slip and make sure you do not water down the ratio of your color to to the liquid you are using as the low vescocity substance. It’ll be different for everyone based on how strong the color you are using is and how much water, milk, mouth wash, whatever low vescocity thing you want to use is.
It took me about 2 hours worth of testing and I've found about 30- 40 mL of whatever low viscosity liquid I was using along with 10 - 14 grams of RIO or manganese dioxide along with about 2-3 medium drops of dish soap worked really well for me. Keep in mind you do not need a surfactant in every case but it helps reduce surface tension a lot, which helps the lower viscosity fluid move easier. I coated my leather hard pot in the high viscocity slip of my choice and added the above onto the pot while it was still wet; Worked like a charm every time. Now before I show you a relatively long video of my tests as well as talk about some misinformation that seems to be prevalent (don’t worry I came with receipts + video proof) I want to go over a few mistakes I made that I do not want you to make as well. While many low viscosity things will work, some of them should not be used either for your own health or the health of the kiln. Here is a list of things I would stay away from when doing mocha diffusion.
Soy sauce: I do not have the proof or brand new kiln elements to track the effects over the course of years to explicitly say that sodium will effect the health of your kiln elements. While I know that too much sodium in a specific form will hurt your kiln elements, I know that soy sauce is mostly water. While it would work It is high in sodium and I find it hard to see the colorants I put into my liquid as it is usually black out of the bottle. I would generally advise against it for those two reasons.
Bleach: While bleach will work I really do not want you to put it in your kiln. On top of that it has a habit of breaking things down and destroying oxygen. Figured this one out when I left one of my good brushes in the bleach test liquid for an hour and it ate about 3/4ths of the brush.
Straight up acid: There is a rumor that acid is causing the finger like interaction (it’s not) and that this is the main ingredient you need for this to work. Of course I had to test it. I tested low acid to high. Everything from base soaps, my own spit, alkaline water, all the way up to the acid crystal potters use to etch their crystals. The assumption was that if acid is doing all the work then more acid should do more work and somewhat scale in activity. But as well know now that's not true. Doing lemon juice is fine, it’s sill low viscosity, it’ll work, but please do not believe the acid pseudo science and assume more acid is better. I do not want you out and about with battery acid or carbonic acid trying to get the most defined branch patterns. Not only is the main ingredient needed not acid, it’ll also put you in danger if you chase the most acidic thing like I did.
The bottom line is : “ if you say it is about acid reacting with the clay, then I should not be able to do it with non-acidic things like bleach, milk, water, and adding soap should kill the reaction because it is a base that kills acidity when added to acidic things” But here we are with video proof. If it is about acidity I should only be able to do it with acidic fluids”
Alcohol: In my Testing with 70% iso
Food coloring as a colorant: you must use something that will not burn off in the kiln. Food coloring will not survive the process. The easiest to use at first is red iron oxide.
Anything that can hurt your kiln or you I need you to stay away from. Did I test a lot of these things in my tester kiln?, yes. Do I want you too? No.
Below is a 15min or so video I edited showing most of my test with different substances with mocha diffusion. Enjoy.
