Tutorial: Using Casein Emulsion as a Medium in Casein Painting

Casein emulsion is an extremely useful medium that you can add to your casein paint to adjust its consistency, enhance adhesion, and increase transparency. It essentially acts as a binder and diluent, much like acrylic or oil mediums in other forms of paint.

I have seen a lot of recommendations for using water to thin casein paints, but I have found that, much like acrylic paint, water will thin not only the pigment but also the binder. This can cause the film to break down and lose its water resistance when dry.

Also, I see most artists using the commercial emulsion straight from the bottle without diluting it with water first. There are no instructions on the bottle that I have regarding mixture ratios between the emulsion and water, so that can cause some confusion.

On the Richardson website, it mentions using water to dilute the casein emulsion, as it is pretty gloopy right out of the bottle. For thin washes they recommend one part emulsion to five parts water, but for the way I paint I have found the ratio of one part emulsion to two parts water to be much more useful, and I can always add a little water to thin it out when I need to.

I use pretty much any plastic squeeze bottle that I can find to hold the diluted emulsion. The easiest way for me is to use a Sharpie on the outside of the bottle to visually divide it into thirds. Then I simply fill the bottle up to the first line with straight emulsion, and the rest gets filled with water.

​Here is a simple guide on how to incorporate a prepared casein emulsion into your painting process.

​Materials Needed:

​Casein Paints

I use commercial tubes from Jack Richeson, but you can also mix your own with custom casein emusion and dry pigments.

​Prepared Casein Emulsion Medium

Again, I use the commercial stuff available from Jack Richeson. I haven't even used up a third of the bottle that I bought eight or nine years ago, and the price is quite reasonable.

​Water (for initial dilution and rinsing; ideally you would use distilled water but I regularly use purified water as well)

​Palette (glass, ceramic, or plastic)

​Brushes

​Step 1: Preparing Your Paint

​Squeeze or scoop a small amount of your chosen casein paint onto your palette. If your paint is very thick or you are working with dry pigment, first dilute it slightly with a few drops of clean water.

​Step 2: Mixing the Emulsion

​For Smooth, Flowing Washes: Use a little more emulsion and more water.

​For Impasto or Thick Layers: Use a little less emulsion, or even mix the emulsion directly into the paint without additional water.

​Using your brush or a palette knife, carefully mix the casein paint and the emulsion medium together on the palette until you have a smooth, consistent mixture with the desired viscosity.

​Step 3: Application and Adjustment

​Begin applying the mixed paint to your surface.

​If the paint drags or feels stiff: Add a drop or two of more water or more emulsion to the mixture on your palette until it flows better. The emulsion will help the paint spread without over-diluting the binder.

​If you want a glaze or transparent layer: Increase the amount of emulsion relative to the paint. This will extend the color and make it more transparent while maintaining the binding quality.

​Building Layers: The casein emulsion promotes excellent adhesion, allowing you to confidently layer colors once the previous layer is dry.

With all of that being said, I regularly dribble my emulsion mixture right onto my painting surface when I am adjusting viscosity or transparency on the fly.

​Step 4: Clean Up

​Clean your brushes immediately with soap and water. Casein is an extremely durable medium once dry, and it will permanently damage your brushes if left to harden.

​Pro Tip: Testing Ratios

​Keep a small test swatch on scrap paper next to your palette. Test your mixture ratios by observing these traits:

​Flow - Does it spread easily?

​Adhesion - Does it stick well to the surface?

​Finish - How does it dry? (The emulsion can sometimes make the dried paint appear slightly glossier or more saturated than paint diluted with water alone.)