Photos left to right:
Mulling red ochre watercolor paint with a beer glass muller.
Preparing to mull red ochre watercolor paint on a microwave plate slab
Mulling Maya blue watercolor paint on the microwave plate slab
Basic mulling kit with microwave plate, beer glass, and two palette knives
Frosted area of microwave plate slab
Assortment of thrifted mullers
Mulling surface of candleholder muller, note the center is not frosted due to being slightly concave
Mulling surface of beer glass muller
Mulling tools: muller, palette knives, measuring spoons, rag for clean up
Part of what originally appealed to me about making my own paint is that it requires very few tools to get started. I will outline the tools I recommend in this blog post.
First of all, what is mulling and why would you want to do it? Paint is comprised of a pigment and a binder that holds the pigment onto your painting surface. Mulling is the process of blending the pigment with the paint binder of your choice. Mulling breaks up the lumps of pigment so each particle is coated in binder. Mulling is not intended to grind the pigment into a smaller particle size. If your pigment is too gritty it is best to refine the pigment further before mulling your paint. Some pigments clump more than others. I work with a lot of foraged clay pigments and homemade lake pigments that clump together even when the particles are very fine. Mulling will smooth out all the lumps, creating an evenly textured paint.
What tools do you need to mull paint? The most important tools are two hard surfaces, one below the paint and one above. These two surfaces act like a flat mortar and pestle to break apart pigment clumps. The most commonly used surfaces are made of glass or stone. If you are using glass as your lower surface, or mulling slab, it should be at lease 1/4 inch thick and preferably tempered for safety. If using stone it choose a piece free of divots.
I recommend using an old glass microwave tray. They are abundant, inexpensive, tempered, and have a lip around the edge. This is what I used for years before I started making larger batches of paint to sell. The microwave tray I use is 11 inches in diameter with a working surface of about 8 inches in diameter. This is a good size for small batches up to a teaspoon of pigment at a time, enough to fill a couple half pans. If you have a larger surface you will be able to make larger batches and have more working space. On the other hand, a small size is easier to clean in the sink after paint making. For the upper surface, or muller, I recommend a flat bottomed beer glass or candle holder. These are all inexpensive items I have found at my local thrift store that work well for mulling.
Both the mulling slab and muller should be roughed up, or frosted, with a rock polishing grit made of silicon carbide. Polishing grit comes in 4 grades or fineness. I recommend using a #2 grit, the second coarsest one. I got mine a a local rock shop, but you can also purchase it online. Alternatively, use some sand or gritty pigment. Frosting the working surface of the slab and muller give them a bit of grip when you are mulling the paint. It can also serve to level out the bottom of the muller if is not completely flat. There is an unfrosted area in the middle of several of my repurposed mullers where the surface is slightly concave. That's okay. Put a 1/2 teaspoon or so of polishing grit on your new slab, add water to make a paste, then mull with this grit until your slab and muller are frosted. Only frost the working surface of the slab. It is easier to clean up if the edges of the slab are smooth (unfrosted). Warning, this makes a loud sound some people find unpleasant. Do it outside or away from others.
Other than the slab and muller you will need two palette knives. I prefer an offset diamond shaped one and a straight one. The offset knife is great for scraping your slab clean and the second palette knife will help you clean off the first knife. If you are using a larger slab you may like a larger scraper to help clean the slab. I bought an inexpensive, thin, flexible piece of steel used for ceramics at my local art supply store when I started making larger batches. It works really well. The most expensive tool in my kit is the offset palette knife. I invested in a quality one and after years of use I do not regret it. You will need a set of measuring spoons reserved for art making (not for the kitchen!). And I highly recommend a notebook so you can record your recipes and experiments.
One more thing to consider is a mat or tray to hold your mulling slab in place while you work. The heavier your mulling slab the less this will be necessary. I use a tray that fits the microwave plate and holds it steady while I work. Other people prefer to use a non-slip mat made from the rubbery material used as shelf liners.
Hopefully this helps if you have been considering making some paint!