Abdi,
If you don't want your paintings to crack, and subsequently suffer the problems that follow the development of cracking, then you would be well advised to either paint them on something rigid in the first place, which would be best, or glue them to panels after they are finished and well cured. The reason it is best to glue the canvas to the panel before painting is that the adhesives most frequently used for that purpose these days are water-based, and the water will likely soften your acrylic ground, weakening its adhesion to the canvas, or the adhesion between the oil paint layer and the acrylic ground. If the gluing is done before the ground has been applied, the water has a chance to completely evaporate before the ground is applied. If the ground is already there, and covered by a film of oil paint, the water is inhibited in evaporating, and it will soak into everything as it spreads, thus affecting the bond between the ground and the canvas, and between the paint and the ground. Professional conservators are better equipped to perform this operation than artists are, but they are quite expensive, and generally will not be able to do it as quickly as we might like. Your preference for a springy canvas while painting may well be compromising the longevity of your paintings, and the acrylic ground you are using is probably going to compound the problem.
Regarding glazing, the wrong way to do it is to thin the paint with a lot of medium, or, worse yet, with a solvent. This results in weak paint films poorly adhered, which will cause problems later. The best way, if one must glaze, is to choose pigments which are transparent by nature, and add perhaps a small drop of linseed oil (or your Liquin) to a pile of paint the size of a large coin, mixing it in thoroughly on the palette with a palette knife (not a brush), and then scrub the paint on thinly with a stiff bristle brush so that it creates a physically thin layer that lets the underlying layer show through. Note that glazing is only a minor component of the techniques of the great painters of the past, most of whom only used it as a refinement in the later stages of the development of a painting to deepen the darkest foreground darks and to create certain special effects, along with opaque passages representing the lighted areas. I think too many people become overly fascinated with glazing when they first discover it, and tend to place too much emphasis on it. It is really a rather limited technique, and if used in the wrong places will interfere with the illusion of three-dimensional depth.
The common method of thinning the paint with a lot of medium will cause the paint layer to be structurally weaker, and will lead to problems as the paintings age. Medium must be bolstered with solid pigment in order to have the proper degree of strength.
The more we indulge in exotic techniques, the more ways we can go wrong. It is best to master the simplest means before going too far off the deep end with unnecessarily complex techniques.
Virgil Elliott
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