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Working with Casein

Casein paint has been used by the ancients on wood panel paintings, wall murals and has also used successfully as a household/architectural paint. When applied properly on the right support it has proven itself to be an archive quality paint.  The glue was developed by old master craftsmen for making furniture and musical instruments, the binder is actually a fast-drying water soluble glue produced from milk proteins. White glue still used today by some cabinet makers is made from casein. At the factory the casein is dried and ground up before it is made into glue. Since as a painting medium (binder) it is only water soluble until dry, it has also been successfully used in conjunction with other mediums such as watercolor and egg tempera.

Casein for sealing or building grounds

Many conservation authorities believe that casein is inferior to RSG as a sizing material or binder for grounds because of its tendency to become brittle with age but, casein glue posses superior archival qualities compared to animal glues for adhesion, sealing and moisture resistance when used on the proper support. Casein is in fact a water soluble material but after time cures into a hard insoluble non absorbent film.

The purpose of a size is to isolate the ground from and reduce the rate of  absorption of a medium into the support. As defined casein performs this task exceptionally well. Due to it’s brittle properties though, it is more appropriately used for sizing rigid or cradled wood panels or fiberboard where it also becomes an excellent choice for preparing panels covered with canvas or paper for just about any medium. Use of casein is also less difficult to use for sizing than RSG because it is less temperature sensitive  once a batch is made and does not require heating to apply.

Another favorable use for casein as a ground is with silver point drawings where it provides more tooth than acrylic gessoes and chemically reacts with the metals to accelerate the patina. Some modern silver-point grounds are made with a blend of casein glue and calcined bone and/or zinc white casein paint. However, any color pigment could be added to create a toned canvas to draw on.

Casein definitively has a matte finish that egg tempera readily bonds to. This practice in turn can also be used to seal panels for oil paintings where it is not uncommon to first layer the under paintings with the faster drying egg tempera.

Since there have been several commercial fixatives marketed consisting of hazardous diluted varnish and shellac resin solutions in solvents like alcohol or benzene, there has been rightful concern among artist in regards to the health hazards from their use.

“Flatiron Building”  40″ x 30″
Colin Campbell Cooper – 1908
Casein on canvas

There is supporting documentation verifying that artists such as Degas and Cassatt used casein glue diluted with alcohol and water as a fixative for pastel paintings. Artist Della Heywood manufactures and markets a non-hazardous  dry media intermediate (workable) and final casein spray fixative sold as “SpectraFix that works great with charcoal, pastel, conte crayon and pencil drawings. You can also make your own (see below).

Making your own Casein Sizing and Paint  

Although Casein Paints can be purchased in tubes and the medium is also sold in a ready to use emulsion or as a light yellowish powder from where the glue is made by adding distilled water to the dried material, allowing it to absorb the water and neutralizing with an alkaline substance such as aqua ammonia or ammonium carbonate. You can find some of those recipes provided by Kremer Pigmente here

However, there is debate as to whether it is any better or easier to make it fresh. I favor the later. Much like egg tempera the best results from Casein are achieved by blending the freshly made medium with Dry Pigment but it will also blend well with higher quality tube watercolors if desired.

The only drawback is, this glue can have a relatively short shelf life where once it starts souring you should throw it away. This means that when making your own casein medium you should make small batches as you need it and to avoid waste and never grind large quantities of medium with pigment unless you intend to use it.  Refrigeration helps to preserve the medium when storing your medium  in an air-tight container that has been sanitized with alcohol first.

Materials needed:

  • 1 Enameled or Pyrex pot (non-metallic)
  • 1 qt skim milk
  • 6 oz  vinegar
  • 4 oz distilled water (tap water is susceptible to bacteria mold growth)
  • 1 oz borax (can be substituted with baking soda, quick lime, aqua ammonia or ammonium carbonate)

It is important to start with a non fat milk also known as 0% fat milk which will not contain the of contamination of unwanted butterfat and other nondrying fatty oils. To assure good separation, the milk should be warmed but do not heat higher than 110° F to prevent destroying the properties of the casein. Extracting casein in a cold solution is also a cause for the inferior formation of casein. This must be done in an enameled or Pyrex pot since some metals such as cast iron, aluminum and copper will react with acidic materials resulting in contamination.  

In making your casein glue you intentionally alter the milk’s already low pH chemically by slowly adding acidic acid (white vinegar) while stirring to turn it sour. When the milk is placed in an acidic state you initiate the precipitation of the gelatinous lumpy consistency (casein proteins) from what is left which is mostly water. Note: This is the sensitive part of the procedure. By adding acid too quickly or the accumulation of too much acid in the solution will dissolve some of the casein. You only need to add enough acid to acquire good separation of the curd and whey. Casein is amphoteric, meaning that it will produce salts with both acid and alkaline states. A higher acidity will produce undesired excess salts once the casein has been neutralized. Therefore it is important not to fluctuate anymore than needed within the pH scale.

Continue to warm and stir the milk until the lumps (curds)  begin to develop and then take off heat allow to settle. The remaining yellow liquid (whey) is discarded by filtering through doubled cheese cloth or linen. 

Wash the casein by blending the casein curds with the addition of clean distilled water and stirring lightly. Allow the casein to separate and drain off the water through a filter. To clean out any remaining fatty oil contaminates, to sterilize the curds, and assist drying  wash the filtered curd with isopropyl or grain alcohol. Sterilizing from contaminating bacteria will make your paint medium keep longer.  Return the casein curd to a clean glass container after laying out on a cotton cloth to allow any excess moisture to dry.

The solid curds are then neutralized with a aquatic alkaline substance where in solution a strong adhesive is made. By the addition of baking soda, borax, quick lime, aqua ammonia, ammonium carbonate, etc., or any alkali substance the casein curds will become water soluble until it dries.

Note: Personal protection precautions must be taken to avoid contact with alkaline substances (especially the eyes). 

Aqua ammonia or ammonium carbonate are most commonly used in casein production but due to their evaporative nature they are also susceptible  to a drifting unstable pH. Using aqua ammonia in your studio would also require sufficient ventilation to remove gaseous ammonia and carbon dioxide fumes. 

Borax is the most commonly used where it raises the pH higher and buffers the medium from drifting acid making it an excellent casein pigment binder. When Borax is used your medium will also keep longer when refrigerated as long as your storage containers have been sanitized with alcohol before using.

Neutralizing with Borax

Dissolve borax in hot (not boiling) distilled water  and add the solution to the casein curd while stirring until it develops a paint consistency. Because this hydrolysis process is slow you should allow to sit 4-6 hrs to be certain the reaction has finished.  This is your Casein medium.

Hydrolyzed lime casein 

Hydrating with (slaked) lime or Fresco Lime Putty makes a durable casein binder. However, due to it’s insolubility and high pH it is best to dilute to a thin paint consistency before hydrolyzing. Caution must be taken to prevent adding too much alkali material since high alkali substances can also effect some pigments. This is especially critical if using calcium hydroxide (quick lime).  Lime is a strong corrosive alkali, be sure to check MSDS for  hazard precautions. However, this can be easily remedied by making gradual lime additions and testing  to achieve a neutral  pH of  7.0 – 8.5 with an inexpensive soil pH meter or by using mineral Pigments used specifically for frescoes. Jellas Pocket Size PH Meter
PH 0-14.0 Measuring Range

Premix your lime in a large plastic or glass container slowly adding distilled water to wet all of the lime into a paste. Continue this dilution slowly until mixed to a thin paint consistency. If using slacked lime putty for this instead of lime powder, dilute to the same consistency. Initially blend  8 – 16 oz of this milky mixture of water and slacked lime by adding in small quantities at a time and while monitoring the pH.

Add the lime paste to the casein curds while stirring. The lumpy curds should immediately start breaking down from the alkalinity of the lime. If it appears lumpy allow it stand while the reaction takes place and then return to stirring until it breaks down into a smooth paint. Allow sufficient time to be certain the reaction is complete. Add additional distilled water in minute amounts as needed and strain through cheesecloth. This can now be used as your medium.

As a size

The above viscous solutions (either neutralized or hydrolyzed casein) are thinned with distilled water to a thinned paint consistency. Two coats will seal well enough to proceed.

As Gesso

Borax neutralized Casein:

  • 1 part titanium or zinc white
  • 3 parts calcium carbonate (caulk)
  • A few drops of alcohol to facilitate mixing into a paste

Once your pigment and caulk is ground to a smooth a creamy consistency, in a clean container blend with your sizing in equal parts of size and pigment paste until it’s a smooth and creamy opaque white. At this time it should be strained again through cheese cloth and can be thinned to use like paint .

Hydrolyzed Lime Casein Gesso

Addition of  titanium white pigment first ground into a paste with alcohol and blended in equal parts with casein medium will make a sufficient gesso ground. The addition of caulk filler is not needed since the lime and pigment will provide adequate opaque coverage. After a few coats this dries to become an absorbent plaster like ground.

Making the paint

Grind dry pigment with a small quantity of distilled water into a wet paste. With difficult pigments such as titanium white  add a few drops of alcohol to break down the pigment. Then add casein medium to desired viscosity. Additional water can be added at this time for thinning.

Keep in mind that a small amount of pigment goes a long way and that all (especially dry) pigments must be treated as harmful substances. Use safety precautions to avoid contact with skin, always wear an industrial vapor face mask  and work in well ventilated areas to avoid breathing dust. Do not eat or drink in the same room as pigments and wash your hands frequently. 

“Solomon’s Temple, Colorado”
20.5″ x 26″ casein on canvas
Samuel Colman Jr. – 1888

Used as a painting medium

Painting techniques used with casein are much like that of Egg Tempera Painting or maybe even more like a lighter version of Acrylic and it dries uniformity into an opaque mat finish that works well for use as an under painting. Casein can be thinned working very well as a transparent wash or glazing. However, the medium does not flow as well as most water based mediums because it dries fast. Where fine details can be painted easily it responds best to daubs and short stokes. Caution must also be taken to avoid heavy layers as not to build up stroke texture (unless it is your intention) since this is a heavy bodied paint.

If the paint has not dried long, errors can be corrected where it can be removed with a damp rag, fine grade sandpaper or a hard eraser. Because dried casein is insoluble in water but is soluble in alkaline solutions, for more difficult areas you can remove the paint gently with a 10% aqua ammonia solution on a rag. 

Note: Unless you can afford to throw away your brushes you must wash them immediately after use. You can usually get all of the paint out with soap and water but, if you have any stubborn medium it can be dissolved in 10% aqua ammonia solution and rinsed with water. Do not allow brushes to set in water. If the binder has had the opportunity to set it is difficult to remove.

Casein as a Fixative

Casein also works well as both a workable and final fixative for all dry pigmented media. It dries clear with a  matt finish that won’t alter pigment hues on canvas and does not interfere with the tooth of your canvas (a plus for layering pigment). Although you can purchase it ready made, it is not a complicated process to make your own.

The fixative is merely a mixture of:

  • 1 part / 2 oz. – casein glue medium (neutralized with Ammonia or Borax)
  • 2 parts / 4 oz. – grain alcohol or water white spirits such as gin, vodka, etc.
  • 5 parts / 10 oz. – distilled water

Blend thoroughly to make a thinned mixture. If  solution is cloudy allow it to stand for a brief period to look for settlement at the bottom where the clearer liquid can be removed from the top. The fixative should then be filtered either through a coffee filter or wet cheesecloth and a funnel where it can be put in a good quality pump spray bottle or air brush. If using an air brush, use in small quantities and flush out well with an aqua ammonia solution after use.

Related links

Images on this page provided by The Athenaeum.

Kremer Casein Recipes – (from casein powder)

Earth Pigments Co.- Recipes for Artist’s Casein


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