In the bowl of a food processor or standing mixer, dissolve yeast in warm water. Add oil, salt, and sugar; mix to combine. Add garlic and olives; mix to combine. Add flours; mix until dough forms a ball and pulls away from the side of the bowl. (This is a stiff dough; you may want to finish kneading by hand.) Place dough in a clean bowl, cover, and let rise until doubled, about 1 hour.
Punch dough down gently and return to bowl. Cover and let rise until doubled, about 45 minutes. Turn dough out onto a lightly floured surface and divide into four pieces. Knead dough slightly, then roll out into rectangles the length of a baguette-style bread pan (about 18 inches). Roll dough up lengthwise and place, seam side down, in a baguette pan or on a baking sheet. Using a razor or sharp knife, make three or four diagonal slashes (about ¼ inch deep) 2 to 3 inches apart along top of each loaf. Let rise 30 minutes.
Heat oven to 425 degrees. In a small bowl, whisk together egg white and water. Brush top of each loaf with mixture. Spray loaves gently with a light coat of water. Place a shallow pan filled with water on lowest oven rack. On middle rack, bake loaves 20 to 30 minutes or until golden brown. Let rest 30 minutes before slicing.