Acrylic - fat over lean?

[Vermis]

A question and a bit of a whinge. Okay, a lot of a whinge:

After struggling with rewettable Atelier Interactive acrylics for two years, I'm ready to follow the example of others on another forum and switch back to regular acrylics. But there's one person who had success painting them 'fat over lean'.
I don't have much experience with oils but I (hopefully) know what that means. But how does this apply to acrylics? Asking on the other forum got me the same reply: "I just paint fat over lean, like with oils." Explaining myself and making a bad joke about linseed oil only got me the internet equivalent of a 'he must be crazy' stare, and "I paint them fat over lean." Along with "You don't use linseed oil with acrylics!"

:nohope:

I dunno if I can ask again without earning myself minus brownie points in that vaguely asspatty atmosphere. And I'd probably get the same answer again. (Funny, I kind of expected it the second time) So, to the conceptartmobile. I guess it means painting increasingly unthinned or medium-mixed paint over water-thinned underlayers, but I'd like some confirmation:

How do you paint acrylics 'fat over lean'?

[Elwell]

You don't. One of the advantages of acrylics is their chemical simplicity, relative to oils. As the water evaporates, all the layers lock together into a pretty homogeneous paint film. So, you can start with thin washes and gradually build up to thicker, more opaque layers, but this really has nothing to do with "fat over lean" in oils.

[DSillustration]

You are confusing 'fat over lean' with 'thick over thin'.
They are not the same.
Fat and lean refer to the oil content of your paint... it has nothing to do with the thickness of application.
For instance, I can can take 'lean' paint right from the tube, and apply it in a very impasto manner.
Or I could dilute it with a lot of oil (fat), and then just scrub it very thinly over the surface.
The two are not synonymous.

Because fat and lean refer solely to the oil content, an acrylic comparison is sort of impossible.
That is why you likely got the 'don't add linseed oil to acrylics' comment.

The closest equivalent in acrylics would be to add more/less gel medium (which acts like a binding agent much the same way linseed oil does for oils).
Like Tristan said, the chemical make up of acrylic renders the rule moot, but as far as surface quality goes, it does apply.
Trying to lay watery washes of acrylic on top of a slick layer of gel medium is not going to be very manageable.
Watered down acrylic has much more tooth, and is more accepting of subsequent layers than a thick rubbery layer is.

I hope that helps.

[Vermis]

Fat and lean refer to the oil content of your paint...
That is why you likely got the 'don't add linseed oil to acrylics' comment.

Like I wanted to say elsewhere: I know that. :P That's why I wanted an explanation about how on Earth the term could apply to acrylic paint. And "I take it you don't mix linseed oil with your acrylics chuckle chuckle smiley icon." A reasonable thing to assume and understand, I'd've thought.

For instance, I can can take 'lean' paint right from the tube, and apply it in a very impasto manner.
Or I could dilute it with a lot of oil (fat), and then just scrub it very thinly over the surface.
The two are not synonymous.

The closest equivalent in acrylics would be to add more/less gel medium

I took 'lean' to include oil paint thinned with turps, spirits etc. too. In which case the rough acrylic equivalent would be ordinary water, right? But again, I know you can't compare oils and acrylics too closely.

Anyway. Thanks for the replies. I had a feeling one answer would be

You don't.

... and that's good enough for me. But it's also moot because I'm off to see if the art supply shop has those new Cryla tubes in.