BLO is not absolutely necessary. I used it for a while because that is what I read here (years ago). For me being a "logical" thinking person kept asking "WHY" is it needed? Answers were pure speculation. Testing by me and a few others (which can be considered purely subjective) did not prove anything one way or the other. If it doesn't help, then it is just an extra (unnecessary) step for me. If it does help, then that is good.
Sharon, above, said in another post on another thread how it aids in the finishing process for the people she works with. It takes a keen observer to notice that. :good: For me, I have some and use it on some woods but not on others. I don't use it to aid the finish/feel or application. I do use it on some amber and brown woods to give it a better tone. I always try the BLO on a cut-off piece to see if it gives me an enhanced color or not. I do NOT use it on holly or blood wood. It makes whiter holly look ivory toned and it causes bloodwood to have a hint of an Orange tint, neither of which I usually want.
I most certainly do not use it on oily woods if applying a CA finish as it can reduce the adherence of the CA to the blank and aid in causing "lifting" of CA at the ends of the finished blank.
Experience and personal preferences should determine its (BLO) use or non use.
Adding in: If you apply CA with paper towel (PT), it could be more beneficial in that BLO aids in adding more CA to the blank, and does lubricate it some. What I mean by this if you apply the BLO to the PT and onto the blank, and then add CA onto the PT over the BLO, more CA will get to the blank. Not using BLO on PT does cause the PT and CA to sometimes adhere to the turning blank!
Again, that is part of the reason I don't use PT. I use applicators that puts 100% of the CA onto the turning blank. (I started out turning pens when living overseas and CA was EXPENSIVE. PT absorbs about 80% of the CA in my estimate/experience. With BLO as a backer on the PT I would surmise that around 50% is absorbed into the PT.