Archival quality of acrylic

Well - going back to front: biros aren't intended for artistic use, and marks made with them change in various ways according to the brand and the colour - reds go brownish, greens fade away, blues and blacks leach through paper, the latter turning brown. They probably won't just disappear for a very long time, but they'll certainly fade badly in light. Acrylics is a bigger subject - provided you're using artists' quality acrylic paint, and not something meant for painting the bathroom, it is not likely to degrade significantly provided elementary precautions are taken, including varnishing completed paintings, using acid-free paper, and so on. Acrylic under oil, for so long as it's a coat of priming we're talking about - a full acrylic painting under oil MAY present difficulties in the distant future - is at least as stable as the traditional rabbit-skin glue and lead priming, except that lead white is generally better for oil paint, and may even be preferable. The thing I would not do with oil paint is use it on stretched canvas with an acrylic study beneath - oil paintings benefit from a rigid surface, and the different speed and means of drying could create problems down the line. The amount of useful advice available in Britain on these subjects is very, very limited. If you look up the University of Delaware, however, and go to their MITRA site, there is a great deal of information which you'll find useful: and there are useful summaries of same on the Natural Pigments website, and Painting Best Practice forum (on Facebook). There's also a page on Facebook run by the US artist Virgil Elliott, who wrote a standard work on oil painting which I hope will be back in print soon - it's called Traditional Oil Painting, and is worth a look. You'll see from this that the biggest areas of concern are centred on oil painting - particularly because of the difficulty in obtaining lead chromate whites, and the habit that many paint-makers fell into of using Zinc White, which is a known cause of delamination (and not just over acrylic), and mixing it with other colours, including - when it was freely available - Flake White. Acrylics do not as yet raise the same levels of concern, largely because they're inert - so the amount of chemical reaction over time should be slight to non-existent. At the same time, plastic does embrittle: so there may be some concerns about that - on the whole, though: acrylic was introduced to the world in around 1948, and in artists' paint in around 1960 - this isn't, granted, the 800 plus years in which we've had oil paint, but issues with acrylics are usually only reported when they've been mixed with other substances, or on ill-prepared surfaces. So - I shouldn't worry!

By the way - the market value won't have much to do with concerns about longevity: art dealers and collectors generally know almost nothing about paint-longevity; it's more to do with prejudices against 'plastic paint' as opposed to 'the old masters' medium'.

MITRA is run by trained conservators, connected to the university. Not sure there's a lot there on acrylic - but take a look. The test of time is, as you say, the acid one - I shan't be around to tell, tragically.....

Robert...stretched canvass, acrylic under-painting, oil on top = bad news. Drat. There goes one of my favourite paintings...a copy of Manet's 'A bar at the Folie Bergere'. Painted exactly in the way you have doubts about. I shall watch it for developments. No big deal, I painted it for me because it's one of my favourite paintings, and hoped I might learn something. It will probably see me out. That'll teach me to stray from watercolour.

Potential bad news, Lew - by no manner of means certain. Provided it's not inappropriately stored - too near a heat source, or moisture, to minimize the movement of the canvas - it could last as long as the Mona Lisa. Thing is, these are ideals we're talking about: the very best practice - but many thousands of paintings have survived well, having been painted with sublime disregard for the basic rules of construction: luck, and the conditions to which a painting is exposed, have a lot to do with it. Bear in mind too that the larger the canvas, the greater the problems - but if you think of one of those huge oil paintings, stuck in an crumbling gilt frame, in the long gallery of a country house which was never properly heated and subjected to the full heat of a summer's day because it was right at the top of the house and had plenty of windows.....you see what paintings CAN survive. I don't think I'd worry in your place .... even at the worst, the painting won't fall off the support. Um. Probably....

For those really (really) interested, this link is, I think, quite reassuring in one respect; less so in another, as it indicates more study is needed on conservation of acrylics. http://www.tate.org.uk/research/publications/tate-papers/02/conservation-concerns-for-acrylic-emulsion-paints-literature-review