Darkening sky

Will be interested to see the effect of the oil glazes on the acrylic John. Not something I've tried before.

I’m not overly keen on combining the two mediums, although it can be done reasonably safely in the order that John is working. Problem I can see here is that glazes are thin, could there be an issue with cracking or flaking in the future? In fact, can you glaze successfully over acrylic, I don’t know! I’ve no doubt that Robert will have these answers, I’m sure he’ll come in on this thread when he reads it.

Crackelature is the word here (it can be spelt in a few different ways). I’m sure that I’ve seen something on the market in the past, Jackson’s would be your best bet John, as their range is extensive! Alternatively, and cheaper would be to wait 100 years or so, tricky that...

Craquelure mediums (Alan's right, there's any number of ways to spell it!) can be obtained from art materials suppliers, but I'm not at all sure they can be used safely, or at all, with oil: they can certainly be used with acrylic. Is it, to quote Laurence Olivier's Nazi dentist in The Running Man, safe..........  Um.  Well - painting oil glazes over acrylic is safest on rigid surfaces, rather than canvas - because the two mediums dry at very different rates, and any flexibility in the substrate is quite likely to lead to cracking or flaking in the longer term.  My own view is - it's worth a try.  Acrylic offers textures that would be very difficult to get with oil, and at the thickness of paint needed would take a long time to dry enough to glaze over it.  Acrylic is obviously much quicker - (as is texture paste).  Painting thickly in oil over acrylic would be a bad idea, but glazing should provide fewer problems. I did say 'should'......  It's a case of suck it and see, though, really.  I would tend to use an alkyd medium, like Liquin or oleogel, with the oil paint glazed over the acrylic; or even use alkyd paints - i.e. modified oil, like the Griffin range.  It may all crack and craze one day, but it should take quite a while to happen - i.e. 100 years or so - if it happens at all.  Obviously, acrylic over oil will fail in a hugely shorter time. If you use any medium other than an alkyd, don't mix Turps or any other solvent with it, because that WILL cause problems; similarly, avoid (as we all should anyway) the use of any varnish, dammar or other, in the painting medium.   And having said all that - I should be very surprised if you encounter any issues in the lifetime of yourself or your grandchildren!  But you could always use those alkyd paints, and glaze over them with fuller bodied oil .... might be a better way to go?

The Craquelure medium is the amateur faker's friend, so far as I'm concerned.  A real art forger would use different materials and methods entirely - it's a gimmicky product. With the proviso that 100 years wasn't a firm figure - some modern paintings have been known to fall off the canvas, bit by bit, after 20 years or even less - I agree with you.  Georg Grosz painted on cardboard - I think his work still exists; and Sir Joshua Reynolds' pictures would often crack before he'd even got them out of the studio, because of his use of experimental mediums - one of his best portraits has been described as "a noble wreck", but it still exists... have as much regard to good studio practice as you can, but don't be afraid to take risks now and then, is my feeling.