Foundation White Ground & Underpainting White Paints

To provide the best painting foundation, the earliest layers of an oil painting should have specific properties. Of particular importance are low oil content (lean) and high support strength. Whites are some of the leanest paints available. Both lead white and titanium white make strong paints.

Lead White or Flake White (PW1):
Chemical: Lead(II) Carbonate
Use where a lean, opaque, fast drying white is needed.

Titanium White (PW6):
Chemical: Titanium Dioxide

General all purpose white.
Tinting strength very high.
Pure titanium dioxide white may express oil to the surface during drying. ⁴

Foundation Ground or Foundation White
When preparing a canvas it is desirable to have a strong foundation in the first layers.  Furthermore, the guideline "Fat over Lean" should be used.  This not only helps prevent cracking later, but also gives the fatter layers of paint a lean "underbitten" surface to "bite" into and adhere to. ¹   And for convenience sake, a fast drying paint may be desired.  

   ~ Lead white, aka Flake white, has all of these properties:

• Structurally Strong White with a Tough Flexible Film ¹
• Leanest White
• Fastest Drying White
• Opaque
• Very Good Covering Ability

   ~ Titanium White is a good less-toxic alternative:

• Structurally, "Less Prone to Cracking" ³
• Less Lean than Lead White
• Medium Drying White
• Opaque
• Superior Covering Ability

Michael Harding carries a Titanium White with dryers to contend with the slower drying time compared to lead: it is called 'Titanium White no. 3.' 

Maximizing the properties of both lead white and titanium white, some artists use a 50/50 mix of the two for a foundation white.  While I prefer to mix my own, the Michael Harding line does contain a paint with this exact mixture: it is named 'Foundation White.' ⁵   If you want to mix your own, ensure you are using pure titanium dioxide and pure lead carbonate paints.   Click for more about: White Paint Ingredients.

Underpainting White
The underpainting portion of a picture is one of the earliest layers painted.  An underpainting white with the properties listed above would be most beneficial. 
   
   ~ Lead white, of course, has all of the properties and "is the most structurally sound white for underpainting" ² and its "tough stringy texture" ¹  makes it ideal for texturizing.

   ~ Titanium White is a less-toxic alternative.

As a final note, zinc white is not appropriate for the early painting layers of an oil painting.  Not only is its transparency and low tinting strength an issue, but also its paint film is too unpredictable for this job. ¹  Furthermore, it dries very slowly.

Please post your suggestion or remark by clicking 'comments' below.


Bibliography
1. Creevy, Bill The Oil Painting Book, Materials and techniques for today’s artist, 1994, Watson-Guptill, New York, pp50-51, p144
2. http://www.dickblick.com/items/01597-1242/#colorpigments 3/3/10
3. http://www.dickblick.com/items/01597-1013/#colorpigments 4/13/10
4. http://michaelharding.co.uk/colour-info.php?cID=75 4/13/10
5. http://michaelharding.co.uk/colour-info.php?cID=78 4/13/10
6. http://michaelharding.co.uk/colour-info.php?cID=77 3/15/10