I'm well through the varnishing operation on my barrister bookcases.
I followed the diluted PU approach using 2 parts Rustins, High VOC ("full-lead"
) satin PU to 1 part white spirit. Initially I was very dubious that it would be too limpid and cause runs but in fact the low viscosity means it runs immediately and can be dealt with rather than a run developing during the drying process.
I'm using 2 coats and getting a satisfying low build coating that is sealing the surface without looking "varnished". Not something I can show in a photo.
Drying time is slow but I can do one bookcase per 24 hrs. I've had to up the workshop heating to 18C and leaving the ceiling mounted dust filter running during drying is helping hugely with the surface being hard enough for de-nibbing after about 10 hours. It does mean applying the second coat just before going to bed but the big advantage is the 24 hr cycle (I have 7 bookcases to do in this batch).
Thanks for the tips chaps