Fixitive before Egg Tempera?

My opinion (as an artist- I’m not a conservation professional) is that any application of fixative to the ground will likely reduce absorbency and add a potentially problematic additional layer to the painting, so personally I would not use fixative as described because it can render the ground less receptive to the paint. A light graphite drawing, in my experience, will not easily intermix with water-based paints, so I think it is OK to just paint right over as long as the graphite lines are enough to guide subsequent work. If the graphite is soft and heavy with some loose particles, you could remove some using a kneaded eraser. Contrary to traditional belief, graphite doesn’t migrate through paint layers- some of Bierstadt’s paintings were actually executed on graphite oil grounds, and while there were some technical issues as a consequence, migration wasn’t among them.

Thanks Matthew,
Sorry for the late response, I just got back in town.
The fixative would definitely reduce absorbency and could compromise adhesion, resulting in possible paint delamination. A light graphite underdrawing would be a fine choice. The harder the lead the less likely the paint would pull up any graphite powder. As Matthew wrote, graphite does not migrate through paints. This is an old misnomer that we are trying to dispel.
The ink underdrawing was used to make sure that the underdrawng did not get wiped away during painting and not to prevent the migration of charcoal, or later, graphite. This does not mean that a heavily applied charcoal undergrowing or one executed in heavily applied, high numbered “B” pencils (eg 8B) will not sully and become incorporated into superimposed paint. This is simply the result of applying a liquid medium over a powdery surface. Even this would only be a problem in the first layer of tempera paint, which would lock up the powder which would be consolidated and not affect additional layers applied over the dried paint.