We know about 'no acrylic over oils', but how about 'careful with oil over acrylic'?

Unable to do much work at the moment, thanks to neck arthritis - that reliable killer of inspiration - I've been mooching through Facebook, and YouTube; and came across the usual - accurate and good - advice about not painting in acrylic over oil; because the paint will bubble and fall off, as once happened to me when I used an oil-primed board without realizing it. But I also found "of course, you can paint with oil over acrylic"; and I thought, well .... yeah.  You CAN.  But as Sergeant Wilson asked, "is this wise, Sir?". I encountered a South African artist a while ago, in an art magazine; it may have been one of ours, or it might have been Artists & Illustrators.  He made a practice of painting in oil over acrylic - that's acrylic paint, not primer or "gesso" - on stretched canvas.  To come to the point more quickly than I often do - I don't think it IS wise, sir.  We know that oil paint adheres well to acrylic priming; don't go panicking about that or allow me to frighten you out of it.  Problems with adhesion can, however, arise if painting in oil over, especially thick, acrylic paint.  As one who wishes you well, I thought I'd just point that out, because I'm aware that a lot of people do it. WHY they do it, I'm not sure: yes, it dries fast, but so does oil paint thinned with Turps/Turp equivalent; so do alkyds; so does regular oil paint plus Liquin.  I wonder why anyone would use acrylic for their underpainting - I never did, he said smugly, even before I knew it might not be a good idea....  So - do you?  I'm not judging you (yes I am; guilty! you're all guilty!), but if you do, my unsolicited advice is, probably don't.

Two questions - Sandra, in relation to acrylic, fat over lean is meaningless: it just doesn't present the same problem (or any problem).  The only caveat, though it's a nit-picking one, is that we've not had acrylics for long enough to be absolutely sure what they'll do in centuries to come (we should be so lucky as to HAVE centuries to come, the way the world is going now!).  Extensive testing has been conducted though, notably by the Golden Acrylics company in the USA, by Daler-Rowney in the UK, and by Winsor and Newton - now gobbled up by Colart - all of which suggests that acrylic can safely be used in this way and in many other ways you'd be foolish to try with oil paint.  And glazing in oil - how is that not lean over fat?  Several reasons (and of course - it can be); one, it's normal, though not invariable, to apply glazes with some oil, over generally lean paint; so that's fat over lean.  But you can also apply transparent paint as a glaze without a medium - in that case, the paint will be so thin as to present no problem.  Even so, I have seen glazes cracking in old paintings - though in very old paintings, cracks are common, glaze or no glaze, especially on stretched canvas or wood that has bowed or shrunk over time.  A more common issue is that the glaze vanishes over the centuries, leaving the original colour showing - so you get blue plants, which would have been represented by optical green as a result of the original yellow glazes. Painters who knew their materials, and then as now, not all did, would use their most permanent colours in glazes; there's been a recent study into this, concerning the paintings of Frans Hals: he used normally fugitive crimson and scarlet lakes over his flesh colours, and they're still there: because he knew his paint, and what would work. Norette, hijacker extraordinaire, congratulations on finding a course at reasonable cost, and I hope it does teach what you're hoping it will teach: I wouldn't personally part with a penny until I was sure it WOULD teach what I was looking for, but though you might think I wouldn't be interested in following courses after painting for so many years - actually, I would: another approach, experimentation, can help us keep going and show ideas we hadn't previously considered.  My problem is just that I'm not fond of following structured programmes - I'd want to jump about (fat chance!) between stages, and do my own thing.   But that's just lack of self-discipline on my part: I'd encourage anyone to take a refresher course now and then, so well done.  (The latest arthritic flare is still coursing its way through my arms and into my hands, so while I'm still drawing every day, holding a paint brush to a board is just too uncomfortable - I lose patience with myself, my temper goes, and I muck it all up!  Were you to feel my bare flesh - I do not encourage this - you would find the affected parts cold to the touch: this has something to do with circulation, I'm told, but why circulation should be impaired by arthritis I don't know.  Still, as someone said, if you can still feel pain at least you know you're still alive.)