Humidity Bloom / White Circular Stains on Oil Painting — Advice Needed”

It’s highly unlikely that anyone in this community would be able to offer advice here. Robert Jones is a possibility so let’s see what he can offer up! This is in need of professional restoration in my view. You haven’t said, but I’m assuming that it’s painted on a stretched canvas, as opposed to a rigid board - so there will be an air cavity between canvas and wall, but I’ve never come across this issue before. Obviously all rooms or buildings where paintings are displayed, whatever the medium, need adequate ventilation and circulation of air, temperature can be important as well, common knowledge of course and probably not of any help in this instance… the damage is done. Restoration is the only way forward, but it comes at a price if you want it done correctly. I guess that the canvas would need drying out and maybe even a sealant added to the reverse. Matching up the small areas of blue colour isn’t a job for the amateur restorer, and of course it may have had a coat of varnish over the painting, which would need removing prior to any possible restoration!

Someone very recently shared the same sort of problem in the facebook group: Traditional Oil Painting.  It may be worth while checking the responses there.

In response to your last question, I think I'd be happier if you used a very small quantity of Linseed Oil; Liquin should be fine,  but I'm never very happy about combining different mediums; Liquin would dry faster, of course...   As to what caused this, beyond the unfortunate effect of very adverse climatic conditions - hard to be sure, but I wonder a) if you used rabbit skin glue as your primer, or an acrylic "gesso", and whether you used enough of either. There's much to be said, as well, for taping acid-free (preferably) paper to the back of a painting, rather than leaving the unprimed reverse of the canvas open to everything from damp to insects.   The fact that you were able to reduce the damage by brushing is interesting, and suggestive of mould, either on the face of the canvas or feeding through from the reverse.     Superficial infestations are usually fairly easy to treat, but more severe attacks are best dealt with by a conservator - that can be very expensive, even if you can find one to start with.  Best of luck with it, because some of the problems here might have been caused at an early stage and thus be very hard to correct   - a lot MAY depend on the initial priming, but lacking that information I can only guess. incidentally, is the painting varnished?  

I was under the assumption that it had been hanging for some years, so now it’s a different scenario! If you’re the artist, then yes, colour match the affected areas and repaint over them… it won’t be that easy, if it were mine, I’d probably repaint a good piece of that blue. Patching in small sections isn’t easy! Two or even three coats of acrylic gesso is advisable before commencing painting with oils… unless you want to go for the RSG method, I’ve done it and it’s time consuming and smelly! As far as I can see, considering that it’s a new painting, there’s no logical explanation for these white patches - I’ve never experienced anything like that myself, in way over a thousand oil paintings… at a guess! Out of interest, what brand of oil paints are you using? You need good quality brand paints like W&N and many others, not cheap imported stuff. Finally, you aren’t using water miscible oils are you?

Agree with Alan re priming.   If you tape paper over the back of the painting, eg a sheet of watercolour paper, or even brown wrapping paper, it's a temporary precaution; if humid and hot countries, you need to keep an eye on both sides of your painting: if any backing gets soggy - just replace it.  Incidentally, I don't do this myself, but then my country is usually anything but  hot and humid.  I don't recommend RSG by the way  - just to be clear. I've heard of the oil paints you're using; haven't tried them, but I understand they're as good as most mid-range paints available generally: not maybe of professional quality, but you did a good job with them; so I doubt they're the problem.   I am increasingly drawn to the thought that it's the surface itself that's given you this problem: two points about that - one, as Alan has said, adding your own priming is a good idea: try not to dilute it with water, though; that can cause problems rather like this; and whenever you buy a new canvas or board, subject it to a good look in a raking light; if you see glittery bits on the surface, in the weave - brush them out or even wash them out, and ISO alcohol is good for that.  Some makers, particularly in hot countries, use an anti-mould preparation in their priming - it needs to be removed to enable proper paint adhesion.  Some also coat their new canvas with shellac - I've never done that myself, though: perhaps I should; I'll read up on it and see what I can find.      There's a very good  book by Virgil Elliott, a US painter, entitled Traditional Oil Painting, which you should find useful: he is an apostle of lead white, which you may not be able to get: it's not easy....   but there are other whites, of course.  And finally - avoid the use of Zinc White in lower layers: I avoid it entirely now; it's very brittle, and can crack and cause failure of the paint film: though I don't think it would have caused the problem you've experienced.   Oh, PS: just to be clear, when I say tape paper to the back of the painting, I mean tack it to the stretchers, or the back of the frame: not stick it to the back of the canvas itself: that wouldn't help at all.    Either way, it's not a foolproof answer - just a suggestion that may help.