Safety

Hello,
There are three ways for pigments to enter your body: Absorption (through skin); ingestion (eat it); and inhalation (breath it). Pigments range from relatively innocuous (used in make-up and food) to poisonous (made from arsenic, mercury, lead, heavy metals).   Toxic pigments are more of a concern in tempera than most other mediums because (1) Tempera artists start with powdered pigments, which are easily inhaled, and (2) the high percentage of pigment in tempera paint (high pigment volume concentrate, or PVC ) means pigment particles slightly protrude above the surface of the paint film; in other words, pigments aren’t fully encased by binder, so toxic colors in the paint film are partially exposed.  Tempera artists often rest their hands on a painting’s surface, as well as sand, polish or otherwise work the surface.  These actions combined with high PVC make a tempera painter more susceptible to touching or inhaling toxic colors if they are part of a palette.
To avoid toxicity, choose a 100% non-toxic palette or take sensible precautions, as you should for any medium.  To avoid skin absorption, wear gloves (“Nitrile” gloves are recommended) or rub on an artist’s shielding lotion (such as “Gloves in a Bottle” or “Skin Safer”). To prevent ingestion obviously don’t stick brushes in your mouth, eat or drink at your work area, and wash your hands diligently after painting.  To avoid inhalation, always wear a mask when handling pigments in powder form. Look for a “disposable particulate respirator” (more commonly known as a dust mask) rated at least N95 (95% filtration) up to N100 (100% filtration).  
However toxicity isn’t the only concern with inhalation –  even if you work with non-toxic colors, dust is an irritant to the lungs and can damage them over time.  So regardless of the colors in a palette, I’m a big advocate of converting powdered pigments to pastes by combining with water.  Once in paste form a pigment is safely suspended and a dust mask no longer necessary. 
There are “shortcuts” to pigment pastes.  Rather than make them yourself you can buy commerically produced pigment pastes, generally known as water-based dispersions (Natural Pigments, Kremer, Guerra are a few companies I know selling them). 
Here is my shortcut.   I make my most often used colors into pastes, then fill the wells of two, round watercolor palettes with them:
Pigments watercolor palette.jpg 
These pastes (no egg added – just pigment and water) dry out overnight, so first thing I do each morning is re-wet them with water using a bulb syringe.  
PIgments re-hydrated.jpg

Most colors reconstitute quite readily, with no mixing necessary; by the time I’ve put on my apron and organized my workspace, they are sufficiently paste-like again. The benefit of this method is efficiency.  Instead of having to go into individual jars of pigment pastes every day to maintain them and extract my colors for the day, my pigment pastes are already out and waiting for me in the watercolor palette.  Granted, they dry out overnight – but not back to readily airborne powders, instead into chunks of dry earth (or “cakes”, which is how pigments were once sold) – and, as discussed, they turn quickly back into pastes with a squirt or two of water. The drawback is that, when dry, they can both attract and generate a little bit of dust, so I cover them when not in use.  As you can see the palettes get a bit messy, but there’s always pure color in the center of the well to draw from when needed. I do keep titanium white separate so it doesn’t afffect other colors’ values or transparency.
Art related health problems are generally cumulative; the effects become apparent only after many years, when it’s too late to undo past practices.  So while many painters find it tedious to make and maintain pigment pastes, I believe it’s really worthwhile to start with good pratices.  It’s good you are thinking about these things.

Koo Schadler