Whether you are a new painter or have been painting for a while you may not know that all paint pigments fall into two categories. Chemical or natural. Knowing this can help you as a painter - forever. It's one more point of knowledge up your sleeve. 

I am really a kid in a candy store when it comes to shopping for art supplies. I spend more time and money on these purchases than all my other shopping ! When it comes to choosing colours you may be like me. I check out the colours that seem to jump off the shelf at me and imagine what they might look like in a composition. But because I also know about natural vs. synthetic pigments I can also imagine how this pigment will behave when mixed with white. Will it stay zingy and bright or will it have a natural "greyed down" effect?  

Chemical pigments will have "chemical-ly" sounding names. Like phthalocynine blue, quinacridone reds,  and arylide yellow.  Sometimes these names are abbreviated or changed on tubes of paint but the pigment number should be listed on the tube so you can look it up on a colour chart to find out what it is. For example PV19 might be listed on the tube. This stands for Pigment Violet 19 and if you look it up on a colour chart or google it you'll find that's the number for Quinacridone Red. Some tubes will have multiple pigments listed on the tube. That's the recipe for that colour! A good thing to know if you happen to run out of that colour.

Quinacridone Red is a chemical colur and so it stays a bright pink when mixed with white - see the image below and compare it to the image of Cadmium Red, a natural pigment, in the image below. This is a property of chemical pigments. If you are trying to create a very natural effect in a portrait you might want to opt for a natural pigment like Cadmium Red instead of Quinacridone Red! Otherwise the subject might start to look a little alien-like!

In fact - for beginners choosing colours or people who want to stay within natural colour ranges you may want to avoid buying too many chemical colours as it will be a struggle to acheive the effect you are looking for.

QUINACRIDONE RED:

 CADMIUM RED:

List of synthetic pigments from Handprint.com: 

monoazo (arylide)
disazo (diarylide)
disazo condensation
benzimidazolone
beta naphthol
naphthol AS
metal complex
isoindolinone
phthalocyanine
quinacridone
perinone
perylene
anthraquinone
diketo-pyrrolo pyrrole
dioxazine
triarylcarbonium

Image source [2]

Image source [3]