Jennifer:
If you add a "drying agent", in the case of Liquin, cobalt dryer to your paint, IMO you sort of negate the whole concept of fat over lean. Fat over lean principles apply when you are applying paint in layers where you want a bottom layer to be dry before you put another over - or at least you want them to dry at a consistent rate with each other to prevent cracking of top layers from a bottom layer drying slower.
Drying agents like cobalt or manganese or lead circumvent that process by making the layers dry faster and more consistent with each other.
You will find differing opinions on Liquin, and on how to glaze. The beading is interesting and I suspect is is due to a slick surface combined with the use of mineral spirits (gamsol) over turpentine. Again, IMO, mineral spirits are great for cleaning brushes, but I don't bring it anywhere near my paint as I don't believe it works in the same way that turpentine does.
EDIT: I believe Richard Bingham understands this MS/OMS vs. Turps concept much better than I do and perhaps we can convince him to explain it.
I remember reading the case for the differences on Cennini and thinking that it made a lot of sense.
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