MITRA Forum Question Details

Hi Roger,

Welcome to egg temepra painting, and to MITRA as well. The following is an edited version of the section in my book, Egg Tempera Painting, A Comprehensive Guide, on pigment pastes.  I've highlighted the section on how to extract pigment from a paste, but included more info that may be of interest.  

Best wishes from Koo Schadler

Pigment Pastes. The most common way to work with powdered pigments is to first blend them with water to form a paste, generally of toothpaste-like consistency.  Distilled water is recommended.  Traditionally, artists (or their apprentices) used a muller (flat-bottomed, glass dispersing tool) and stone or glass slab to combine powdered pigments with water. 

However most modern painters find mulling pigments into pastes laborious and unnecessary.  Fortunately, most pigments readily combine with water. Additionally, there's a second opportunity to disperse pigments: when tempering (combining pigment and yolk medium) - this is when I focus my energy on good dispersion.  Hence many painters (myself among them), to make a pigment paste, simply place powdered pigment in a jar and add water until a paste naturally forms, no stirring or dispersing needed. Add as much water as necessary to achieve toothpaste-like consistency.  Some colors do this instantaneously.  Others need a few minutes (and perhaps a bit of stirring) to combine with water.  A few pigments are 'hydrophobic'; they resist water and need a wetting agent, as discussed below. 

Colors that actively resist combining with water tend to be very light in weight, and/or have small particle sizes (i.e., most modern, synthetic organic colors).  The pigment floats atop the water, forms little balls and rolls away. A dispersant or wetting agent breaks surface tension between a hydrophobic pigment and water, encouraging the two to combine.  Alcohol (95% or higher isopropyl, grain or denatured) can be used.  Oxgall and glycerin work too.  Guerra, Natural Pigments and Golden (among other companies) sell commercial wetting agents specifically made for water-media paints.

Store homemade pigment pastes with a shallow layer of distilled water on top to prevent them drying out.  When you need a bit of paste, simply dip the tip of a palette knife through the water until you reach the paste, then take out whatever quantity of paste is needed.  I store pigment pastes in one-ounce jars, as my paintings are small and require little pigment.  Metal lids can rust and fall apart over time, so use plastic jars (sold in the craft sections) or glass jars with plastic lids (however glass is more prone to breaking, a concern if you have a hard studio floor).

Pigments in paste form, kept in a closed jar, may stay hydrated for weeks or longer depending on the pigment and atmosphere they're stored in.  In time they will dry out, so periodically check pastes and, if they're drying, reconstitute with water.  If you have the space, refrigerating pigment pastes can slow dehydration and inhibit mold, but be sure to keep them away from food.  You can also freeze pigment pastes, although this may change their consistency once thawed (however, do not freeze egg tempera paint).

Mold.  Periodically check pigment pastes for mold.  Earth pigments and some of the synthesized organic colors in particular may eventually sprout strange green hairs or grey fuzz. If you find mold on the top of a paste, you may be able to scrape it off and/or spritz it with alcohol; but you don't want mold within a paint film, so if it appears widespread, throw out the color and start fresh.  Mold spores, as living things, need food, moisture, and air - so you can discourage mold by maintaining a thin layer of distilled water over a paste to keep out oxygen.  You can also add a mold deterrent, but add only to mold-prone colors. Here are a few options for preservatives:

•  Phenol (or any pharmaceutical-grade biocide); available at Natural Pigments

•  Clove Oil, Tea Tree oil

•  Alcohol

•  Pigment Cakes. One more option to prevent mold is to intentionally let a pigment paste dry out. It will form a chunk or 'cake'; hence it's no longer a powder, dust is controlled and, with no water, mold doesn't grow.  You can rehydrate chunks of dried pigment back into paste as needed by simply adding a bit of water.   

Not all colors are converted to pigment pastes.  Ultramarine blue solidifies into a dense mass and most painters prefer to mix it with water as needed (however I haven't found it too problematic and always make it into a paste).  Titanium white also is generally not mixed with water beforehand.  To maximize its opacity, many artists prefer to minimize the amount of water added to it, as thinning with water decreases opacity.  Hence titanium is often tempered as a powder, directly on the palette.

COMMERICAL DISPERSION.  These are water-based concentrations of pigment, with no binder.  They're commercially produced by dispersing pigment and water in a mechanical paint mill.  Essentially, they're pre-made pigment pastes, and can be used with any water-based binder (gum Arabic, acrylic dispersion, casein, egg tempera).