Acrylics under oils

Just Paint has an article by Golden Acrylics on the use of acrylics under oil.  It's nothing to worry about, but worth a read. https://justpaint.org/revising-our-recommendations-for-using-oils-over-acrylics/?fbclid=IwAR3Og5AWBo-dUOm9olnINLG93hXk23cyCkwJ-rqyTixMPqSrQkFpiqjOgNI A massive link, I'm afraid - highlight it then click to activate it. Golden, who also make Williamsburg oil paints, do extensive testing on their products, and have discovered that under certain conditions, oil over acrylic can crack: this usually (always?) shows itself while the paint is drying, rather than longer term.  My take-away conclusion is that acrylic grounds - sometimes called 'gesso' (annoyingly!) are safe.   Thicker underpainting, on which oil paint straight from the tube is applied, not so much. In general, I don't like working with oil over acrylic underpainting anyway (painting on acrylic priming is a different matter) and would be particularly cautious about painting in oil over glossy acrylic.  My underpainting is done with the same paint with which I intend to finish the picture: and that's what I recommend.  This information might be useful for some of us, anyway.

Yes, THIN acrylic.  Not that I've ever encountered any problems at all with painting in acrylic and oil on top - I haven't often done it, but know others who have - but if a manufacturer says watch out - I do. This being in a hurry thing.... if I'm in that much of a hurry, I put the painting off until the next day....  It takes no time at all for an earth colour, thinly applied, maybe scrubbed on with an old brush and then evened out by rubbing it with a bit of cloth or kitchen towel, to dry well enough to be painted over; you might pick up a bit of paint, but not enough to matter.  Might even help a bit!   Latest advice from US manufacturers and guides - who I have to say look into these things a lot more thoroughly than we tend to do in Europe, with the possible exception of the Rijksmuseum staff - is to keep Turps to a minimum on the grounds that it weakens the paint.  Again, I've not personally seen evidence of this, but it's so easy to do without it that I generally do.  

Quick one: acrylic primer, usually referred to, though entirely inaccurately, as 'gesso', has a very good record as a surface for oil painting, and needn't cause any worry at all.  The actual acrylic paints that artists use may not be so safe - there are major differences in the formulation, which I don't have the scientific knowledge to explain, between paint and priming - degree of gloss being one.  The possible issue is one of long-term adhesion - of the acrylics I use, mostly Chromacolour and  Daler-Rowney Cryla, I was told long ago that Chromacolour should NOT be used under oil (by the man who used to make it when the company was based in Canada): it's bound in a resinous compound that is vulnerable to oil and solvents; and it is not like the majority of acrylic paints in that respect.   Paintings in Cryla, or System-3, have, I know, supported subsequent oil painting - for some 50 years so far in cases known to me; but it's worth remembering that an oil painting's life is reckoned in hundreds of years, especially when it's painted on a flexible surface.  I'm really not at all sure that artists' acrylic paint, as opposed to primer, offers sufficient tooth for overpainting in oil in the longer term.  While people must and will make their own minds up, if you were to ask me I should say don't do it because it's not worth the risk.  If there IS a problem, it's bad news for some artists who have routinely painted in acrylic - I suppose to save money - and then glazed over it in oil.  But there it is - I wouldn't do it, I believe in sticking to one medium in one painting, by and large.  There's a myriad of ways in which you can combine all sorts of media, but oil is unique among them in that it's best thought of as a living thing - it continues to change, in so many ways, over very many years. To summarize: Chromacolour and, if it's still made, Procolour, should not be used under oil paint.  Daler-Rowney's and Winsor and Newton's acrylic ranges can be, as can Golden acrylics, and probably Liquitex - even so, I wouldn't use them, personally, as a substrate for oil.  I'd be even more wary of using 'Open' acrylics - those than can be re-activated - under oil.  But opinion is divided over the use of 'regular' acrylics under oil, and the truth is we can't be sure at this stage - ask us in 300 years....