In Peter's book "The Bread Bakers' Apprentice" Peter says to use gluten flour from stage 2 of his seed sour dough starter recipe.  Does this mean use 100% Gluten Flour, or does it mean unbleached flour fortified with a percentage of High Gluten Flour ?  If the latter, then how much GF should be added to the regular flour.

I can buy HG flour locally, it is a grey colour.  I have never been sure whether to use it at 100% in a recipe that calles for HG flour to be used.

Thanks.

Paul.