TheLandscapePainter This is very interesting thread, I am interested what happens there from chemical point of view. My assumption would be presence of non-drying oils in composition that may have separated due to gravity and were on top. Do you remember if you mixed the liquid clear before using?
I always wondered what is that liquid clear but never found a good description online. I saw that it has a jelly consistency and was wondering what makes it jelly.
Just to be clear I do not have liquid Clear so, this is just my assumption about what potentially can leave a tacky surface and based on comments that I read everywhere on internet. Non-drying oils do not dry over years. Also if there is linseed oil in the composition it may be not clean enough by chemical processes for artistic purposes (resins, unwanted fats, etc are still there).
Regarding smooth canvas, you always can make a double solvent: Artistic Linseed oil and Paint thinner/OR turpentine. Proportion will vary depending on the objective. You can dip brush into such solvent and then mix it with your paint. It will give even creamer texture that is easily to apply to canvas. If you plan layers in the first layers you can use mostly thinner with less oil and then add more oil in the mixture as you progress in your painting. (Fat over lean rule). I do not use any of magic white/liquid clear or any of the home made recipes now as I find it unnecessary - normal mediums solve my problems.
Anyway I will keep an eye on this post as I am very interested what the resolution of this problem gonna be.