I was recently told, that a fellow painter had the problem that paint was falling off his paintings after 3 years or so, so I asked why this might be and I was told that he apparently painted lean over fat. Since I have been learning to paint with oilpaint by myself, this was the first time I heard about the idea of painting "fat over lean". I did a bit of research, but still I have some questions.
If I have understood it correctly, basically painting "fat over lean" means to paint slow-drying layers over fast-drying layers, so that layers that are untop don't dry before layers that are underneath. This usually means to paint whith more and more oil.
Now I'm no expert in chemistry , but I would guess that dry layers lose flexibility and volume? Wich would mean that layers that are already dry and untop crack and start to fall off, as soon as layers underneath lose volume.
What if I paint over a layer that is already dry (let's say I let it dry for half a year or more, depending on thickness and pigment)? If I'm not mistaken, there should be no problem?
Also, what happens if I use a glaze? glazes usually dry fast. So I should not use a glazing-medium unless the underlying layer is completely dry? Supposedly Liquin adds flexibility to dry oilpaint wich on the other hand should mean that you could use it regarless. Alkyd-oilpaints are said to be very flexible after drying as well, nontheless I've read that you should not use them untop of normal oil-paints. So, what's the case?
thanks for the help