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Casein (kay'seen) is a quick-drying, aqueous medium using a milk-based binding agent, and is one of the most durable mediums known to man. Nine thousand year old casein cave paintings have been discovered in Asia, and later, the medium was used by Byzantine, Roman and Renaissance artists including the Old Masters.
Known for their versatility and array of capabilities, casein paints can be used to create a variety of effects from the rich opaques of oil to thin watercolor washes. Because casein has an exceptional integrity of color and always dries to a perfect matte finish, it is unexcelled for art reproduction. The velvety matte finish can also be buffed to a satin sheen or varnished to produce a resemblance to oils. Over time, casein pigments become resistant to moisture and as history has proven, the medium has a durability and permanence which has easily stood the test of time.
Casein differs from other media, yet it shares many of the same characteristics, which make it a very versatile medium that lends itself to many techniques. Casein has the wash capabilities of watercolor, the smooth opacity of tempera and gouache, and the richer textures of oils and acrylics. Brushes dipped in casein keep their finesse, producing clear, crisp lines. Unlike oils, casein is a clean, water-soluble medium requiring no strong solvents. And because it dries quickly, it's possible to lay on a glaze and move onto the next stage within a few hours instead of waiting for days, or even months, for oil glazes over oil to dry. In comparison to watercolors, the main advantage of casein is that it's easily correctable. It can be removed with a cloth, brush or eraser.
Are caseins archival?
Yes. Properly cured and with a protective varnish, caseins can last longer than oils, especially oils on canvas. They also will not crack or yellow.
How should I apply caseins?
You can apply caseins “juicy” like watercolors, impasto like oils or anything in between. A rigid surface, such as a canvas panel, is critical when applying casein thickly (to prevent cracking if the surface is flexed). You can use a painting knife, brushes, cloth or even your fingers to apply casein to your surface.
Can I mix casein with other paints and mediums?
Use casein over watercolor or gouache or as an underpainting for acrylic, pastel or oils. If using casein under oils, apply a barrier layer of Damar Varnish over the casein before applying the oil paint.
Does casein colors change betweenwet and dry?
Wet casein does look about a shade darker than it will when it dries. Get to know the paint by making yourself a color-mixing chart.
Are casein paints transparent?
The degree of opacity varies from color to color, with white being opaque and affecting the opacity of other colors when mixed with them. When you make your color chart, we recommend that you include a section for each color combination to be applied over a strip of a mid-tone gray or black to create an opacity reference.
Casein & Underpainting?
Casein is also the perfect medium to use for underpainting. As long as an artist doesn’t lay on casein too thickly, it’s an excellent choice for underpainting because it’s insoluble once it cures. The casein will easily accept the oil and will form a good mechanical bond. Using acrylic gesso works fine with casein or oil paint because it has an ‘open’ surface to accept the paint layer and form a mechanical bond.
Why does the color chart show a 95% color + 5% white wash?
Adding a touch of white to your casein colors will help you control your washes. 5% white will make washes lighten gradually from opaque to transparent instead of changing too rapidly.
What is half-tone black?
The pigment in half-tone black is more finely dispersed than in the other casein colors. Think of it as a separate, transparent color, not “pale black.” Half-tone black is meant to be applied as a glaze. Use it on your color mixing chart to show the effects of half-tone black over other casein colors. For instance, half-tone black over burnt sienna results in a beautiful purple.
Can I paint on stretched canvas?
Casein can be used on canvas, but only in very thin applications. Because cured casein can be brittle, we recommend that artists paint on rigid surfaces. If you want the texture of paint on canvas, canvas panels are the best solution.
Can I paint on watercolor paper?
Rigidity counts. You can paint on 140lb. watercolor paper if the painting will be properly framed shortly after completion. 300lb. paper is a much better choice because of its stiffness.
What about other surfaces?
Casein can be used on interior walls, metal, wood, laminates, metal, glass or ceramics. Clean the surface thoroughly. On walls, metal, wood or laminates, prime the surface with a couple layers of gesso or a PVA glue such as Weldbond (mix 50/50 with water). For slick surfaces like glass, ceramics or metal, use denatured alcohol to thoroughly clean the surface. You can then prime the surface with a PVA & water solution as above.
What grounds can I paint on?
Rabbit skin glue, PVA glue, watercolor ground, clay ground and acrylic gesso. Make sure there is no oil in the grounds.
What should I use for a palette?
Because casein will stain plastic palettes, a butcher tray, porcelain tray or a glass surface backed with a mid-tone gray paper provides an excellent mixing surface. Alternately, a disposable paper palette can be used for convenience.
How can I keep casein from drying out on my palette?
Keep a spray bottle of water handy and spritz the paint on your palette periodically. Covering your palette with plastic wrap (after spritzing) and putting it in your refrigerator overnight will keep it especially fresh.
What kind of brushes work best with casein and what is the best way to clean them?
Casein, like acrylic, can be rough on brushes. Its heavy consistency can also be an issue. Use bristle brushes or synthetic soft hair, but never use one made from sable! Keep your used brushes in a brush washer with the heads partially immersed in water until you clean them with water and dish soap. For especially stubborn colors, add a bit of ammonia to the soap before washing. Rinse very well and be sure to re-shape your brush head before setting it out to dry. Brush cleaners and conditioners are another way to keep your brushes usable for years to come.
What about glazes?
There are three methods of glazing caseins to avoid inadvertently lifting a previously painted layer.
Method #1: Wait two to three weeks until cured.
Method #2: Wait until casein is dry to the touch. Prepare your glaze by adding a small amount of paint to water or to Casein Emulsion. A little goes a long way – just be aware that Casein Emulsion used “straight” in this manner will dry to a semi- gloss finish, not casein’s usual matte surface.
Method 3: Use a PVA glue such as Weldbond. Mix 1 part Weldbond to 3 parts water. If your painting is small enough, it may be easier to pour the glue solution over the painting and tilt it to cover the entire piece instead of brushing it on.
What about varnish?
Varnish is a matter of preference. A gloss varnish intensifies the color, while a matte acrylic varnish will preserve that “authentic casein” look. Wait until the surface has cured 2-3 weeks and no longer reconstitutes with water and then apply the varnish in the same manner as you would for an acrylic or oil painting. If you don’t have time to wait, you can use a spray varnish (applied in light coats in a well-ventilated area) within a day of the painting being dry to the touch. The casein will continue to cure even when varnished in this manner.