Fat over lean in extended painting sessions

I'm working on a new painting, which I quickly discovered is way beyond my abilities. Long story short, I think I'll need to go at this in several sessions. It's full length, so I expect to be doing a hand here, a foot there, with tweaks in the coloration, halftones, etc.

So, I'm concerned that I'll be working in enough sessions that the fat over lean rule is going to be a problem. How do you control the fatness of paint in later situations, if you don't really know how many layers you're going to need?

Here's what I want to do, is this going to be a problem?[list=1][*]Thin underpainting in one session based on color studies, using paint + 50% Turpenoid and linseed oil mixture. The ground is a non-toned titanium acrylic gesso on panel, with a graphite drawing.[*]Second semi-finished layer using paint w/no additives[*]Third touch-up layer using paint + several drops of linseed oil, premixed on palette[*]Fourth and so on using more linseed oil until I finally give up and start over[/list=1] All of the paintings I've done so far have been in 1 or 2 sessions, so I don't usually worry about this. I did look for this question in the archives (searched "fat over lean") and didn't find it. I'm actually embarrased to ask, since it seems I should already know.

[Kimberly Dow]

I do not have an answer for you, I have one of my own that maybe someone can answer when they answer yours.

I've never used mediums, until now that is. I was running out of one color and found I used too much linseed in places. Unconsiously trying to stretch the color. Can I paint pure color right on top of those shiny areas that occured?

[Chris Saper]

Lisa,

I am not sure why you think your approach would be a problem. If you are painting discrete areas of the canvas at different times, each area should be just a single/ double layer. If you, for example, are painting hands but covering the whole surface, well that's another question.

If you really are interested in the chemical/technical implications, you might think about posting your question on the Cowdisly site, which is quite focused on materials.

Here's the url: http://groups.yahoo.com/group/cowdisley/

[Marvin Mattelson]

Fat over lean is the basic rule for building paintings that will endure. The basic principle is to ensure that the lower layers dry faster than the upper layers. If the upper layer dries first, this will result in cracking.

There are three things to consider. Thicker paint dries slower than thinner coats so thinner paint application in lower layers is one thing to keep in mind. Certain pigments dry slower, ie.cadmiums, ivory black and titanium white, so you might want to avoid them in lower layers. The more oil that

Chris, I thought my method would be OK but I wanted to check. To be perfectly honest, I am probably stalling, and calling it research.

The last painting I did was more photorealistic than previously, and I found myself tweaking here and there for over a week. Though most areas are 2 layers, I used 3-4 in small smaces like the lighted side of the nose. This had a nice subtle effect and I was pretty happy with the result but I used raw paint over raw paint and I hope that's not going to be a problem during my lifetime.

Marvin, thanks! This is what I wanted to know exactly. I remember a conversation you had with Karin Wells where you mentioned layer thickness as another factor. Your explanation here is gratefully received!

[Tom Edgerton]

Lisa,

You're right to be concerned with all of this, but also remember that oil is a very tough, resilient, and forgiving medium. It will take a lot of experimentation and abuse before it implodes. As long as you're building in relatively thin layers, and not piling it on a quarter inch at a time with a trowel, it will hold up as well as you need it to.

Enjoy the painting, and don't feel as though you're walking on eggshells--it impedes creative exploration.

Best--TE