Stable Instability. Pouring Oils..

This is a big question so I think that I will answer within the body of your question(s). My answers will be in red.

Hello MITRA,
I might win the prize for bringing the most problematic query to the forum. The reason being that my methods of using oil paint are unorthodox, and I don’t have the most scientific of minds. But please don’t be too hasty to judge my methods. I have spent years of time and money getting to the point I have, and I am approaching you now seeking a little reassurance/guidance, but also knowing that you may not be able to give it.
Where to begin. Essentially, I dilute oil paint to the extent of being able to pour apply it (alarm bells ringing already, I know).
This is only a problem if you are diluting the paint with a superabundance of solvent. Pourable should be fine, watercolor wash-like would not.
I mix oil paint in different concentrations, with a combination of solvent and medium, that when poured onto a flat laid rigid support (these days a primed Aluminium Composite board), they interact and react against each other in desirable and unpredictable ways as they meet and combine- natural forms, even fractal patterns, appear within the very dilute paint. detail.jpg Once this layer is dry, after a few weeks, I paint glazes on top in a more controlled manner. 
What I seek in pouring oils, is a contradiction really: Stable instability.
I know the basics…that if you just dilute oil paint with solvent it can’t bind properly and will chalk off.. so I’ve always been careful to add oil/alkyd medium of some kind. I also know the fat over lean rule. But when I am throwing it all on together in one liquid layer- I can’t really apply it that rule in the same way… 
Diluting is not the problem, it is over diluting. In addition, adding additional binder changes the whole dynamic. The aim is to create a paint that moves in the manner you require AND that contains the proper binding strength to avoid flaking, powdering, or delamination.
Having the disparate paints flowing into each other does mitigate some of the issues encountered when layering paints with vastly different PVCs indiscriminately. The addition of the proper amount of alkyd medium to this “soup” would probably make this less of a source of concern as well.
The first year I was making paintings like this I used just solutions made of Turpentine and Linseed Oil, but I encountered drying and yellowing problems which I since have understood… I then adapted my method and started using drying mediums instead of linseed oil.
Most mediums will yellow if there is too much in the paint film. Yes, linseed oil yellows the most initially but all will contribute some yellowing overtime. You were probably adding more linseed oil to the mixture than was necessary to compensate for the dilution. Did you see any wrinkling?
The main successful recipe I have used is:
– Liquin mixed with Zest it solvent, and Oil paint.
This would work but honestly, the gelling component in the Liquin (if it is the standard Liquin) is fighting the ability for the paint to flow. The Liquin is specifically formulated to hold the stroke where it is put. If I were attempting this, I would use a flowing alkyd solution medium (like Galkyd but there are many suitable versions of this on the market) in just the proportion to create a stable film with the desired gloss and no more.
I think and hope I am using enough of each, for the paint to be just strong enough to cure and not peel off. It has has made many successful dry and even paintings over the last 3 years. It gives a very thin, flat surface, almost like watercolour, once dry. It has had and almost enamel surface which succesffully took glaze on top. But I do find that it has sunk in significantly since I changed primer to Thixtropic alkyd primer (which i thought would be better on Aluminium panels) but I have read that some primers make sinking in worse.  I used to use an oil primer, which I think I will return to. 
The more absorbent the primer/ground the more you will see sinking in.
Q: Does it matter if a painting surface is sunk in… if I don’t mind the look of it being uneven? Is the worry that any varnish will bond with the paint and not be able to be removed? – does this even matter? Can I use a few thin coats of spray retouching varnish to seal it and then later a proper varnish on top? Would that top layer of varnish be able to be removed if I did that? Is there a big danger of the painting yellowing /darkening a lot like this, even if I use thin layers of spray varnish? (winsor and newton).
The only problem with the Liquin is that it darkens over time, and actually has over quite a short period of time in recent paintings: compare detail (liquin) early 2017.jpg with detail (liquin) late 2017.jpg . I don’t mind how it has changed and darkened.. but I would like to know if you think it will continue to darken more and more..
 Because of this darkening issue, but still wanting to avoid yellowing oil.. The second and most recent recipe I am trying is :
-‘Drying Poppy Oil’ with Zest it solvent and the oil paint. 
The yellowing seen with Liquin would likely occur with the poppy oil as well. I believe that you are just adding too much additional binder to your pourable paint.
I have started experimenting with this because poppy oil is supposed to be good for pale colours… and I use a lot of white, very pale and muted colour fields. (which is another issue.. finding the best white for using large amounts..currently using Permalba Original. But thinking of trying lead white?! As if I hadn’t already made like hard enough for myself!). drying poppy oil detail.jpg  I knew poppy oil itself would be far too slow drying for what I do, but thought the one with driers added to it might work? The early stages of the experiment and I have managed to achieve a dry and even surface.. glossier than the liquin ones. But I have yet to try painting glazes on top of this layer. Q: I have heard that poppy oil is more likely to crack, is this true also of drying poppy oil? In which case, would you say the surface I have now that seems smooth and slippery, will eventually crack over time?
It is true that poppy oil creates a less satisfactory film than linseed oil. Many will debate whether this is important or a very minor issue. I would personally use a fluid alkyd paint medium diluted in a proper amount of solvent if I were attempting your technique using oil paint rather than any of the unmodified drying oils.
The uncontrolled addition of driers with contribute to embrittlement and even yellowing. In the proper amount they can be a godsend. Again, I would use a fast drying fluid alkyd medium which already has the optimal amount of driers added by the manufacturer.
I am certainly an advocate for lead white when used on traditional paintings, but I don’t really think that it would add that much to what you are seeking, especially as you are painting on panels. The lead white contributes flexibility and film stability but it is inherently more yellow and possesses a significantly lower covering power than titanium white both of which appear to be needed in your work. It is also important to not add too muc medium in your final glazes. Glazes are inherently more transparent and therefore, unable to mask the certain yellowing of the binder.  A proper glaze consistency is likely less fluid that you think. Some of the spreading of the glaze should be by spreading with the brush .
So there you have it.
I don’t know of any oil painters historically to employ methods like these, I do know artists that have done this kind of thing using Acrylic or resins. I can only find one other artist online that claims to be using a similar technique in oil: 
https://mauricesapiro.com/viscosity-series-poured-paintings/
But other than his comparative technique, I have not found any other information to help me navigate this process. I suspect that would be because it is unadvised to be diluting and pouring oil paint in such a way for all the potential instabilities it causes..  But it is partly the instability that makes me want to paint in this way in the first place! You see the dilemma!
I am happy with the paintings currently as they are.. in the short term, they seem stable. But I am concerned with the long term. I would obviously like to avoid Extreme yellowing and and peeling off of any paintings in the future! It is not the end of the world if they change and crack a little bit. But if it is going to be a lot, then I would feel unethical in selling the works. OR I do you think I should include a clause when selling that says I can not vouch for the archival quality of the work?
I am aware that what I am trying to achieve would be probably be far easier and perhaps more straightforward if I used acrylics instead- (it would sure be a lot cheaper!)… but I am not quite ready to give up on the beautiful effects I can achieve using oil paint, everything I have invested in experimenting. 
Yes, acrylic dispersion paints are easier to experiment with and be confident it producing a stable paint film. I also understand your desire to continue using oils.
Any tips, or even educated guesses, on ways I could be doing this better – mediums that are good for making a strong but pourable paint film?! Ratios I should keep to? or other ways to keep the work stable for as long as possible… would be greatly appreciated. Thank you! sorry this has been such a long and confused essay…
I discussed some of this above. It is really not possible to give exact ratios other than to say that the paint should not be diluted beyond a pourable consistency. I would do some tests with different concentrations of added alkyd on scraps of canvas or panel to find a happy medium between paint that is not too fat which would yellow and one which is underbound.  
I hope this was of some help. In addition, others may have suggestions as well. Finally, feel free to ask for clarification if I missed something here.
 

Let us continue the inter-text response, again in red.
Thank you Brian for combing through my questions so carefully, that was very helpful! Most especially to hear that I am not deemed as crazy for trying to dilute oil paint to the extent of pouring it. That’s been a big anxiety of mine! Now that it just about finding the right ratio, I can move forward more confidently. 
So just to clarify- you think that (winsor and newtons) dying poppy oil, and a fast drying alkyd like liquin, are both as likely to darken/yellow over time, but that the alkyd will probably make a stronger paint film – so that’s why you’d probably use it instead of the drying oil? 
Yes, those are my thoughts.
Also do you think I should stick to using Titanium white then, if I am using large quantities and want it to have the least chance of yellowing? Do I need to be looking for one that is bound with a lighter oil than linseed and has no zinc in it? There are so many kinds out there, is it worth going for something like Holbein’s quick drying white, which is supposed to be good for underlayers but maybe its ok as the main layer too? or Holbein’s ceramic white? Although its supposed to be slower drying which might not be good. 
Again, lead white is more flexible in the long-run, but for your needs, I do think that titanium white with a solvent/alkyd medium would probably be the smartest choice as a compromise between opacity, resistance to yellowing, and flexibility. Others may disagree.
‘ I would do some tests with different concentrations of added alkyd on scraps of canvas or panel to find a happy medium between paint that is not too fat which would yellow and one which is underbound.’
This is exaclty what I am starting to do now, a controlled test that I should have done years ago..trying differnt ratios out. 
My only concern is being able to tell when a paint film is underbound or too fat… If the results I get, in the short term seem bound- I can scratch them and the paint will not come off!… I suppose I still can not guarantee that in the long term they will stay that way? I have huge worries about them suddenly peeling off one day.. is that completely unlikely if they seem so strong now? I think I can live with darknening/yellowing but chalking off terrifies me obviously. 
The scratch test is really what you have in a simple studio situation. I would probably determine the ratio that allowed for a stable film in the short term and then add a touch more alkyd to surmount possible delamination in the future. Again, this is relating to your single layering sytem. More complicated layering should have a little additional medium added to each subsequent layer.
Essentially I am wondering how to proceed with selling works that I have not proved the stability of, beyond a couple of years. Can i ethically sell them, do you think? Or is that uncertainty just something that comes hand in hand with buying oil paintings (especially of an experimental nature)?. I know you’re not a lawyer, but your personal opinion, as a conservation expert, would be gratefully received.
You can only do your due diligence and use the most stable materials and techniques that allow for the fulfilment of you aesthetic aim. This is what you can do to be an ethical creator. Anything beyond that is on our shoulders 😉
If this is keeping you up at night, you should really experiment with a similar effect but using acrylic dispersion paints modified with some of the plethora of acrylic dispersion mediums and tested additives. As I wrote before, these are more forgiving of breaches in practice than are oil paints.  I understand your comfortability with oils, but what could it hurt to experiment? You may even discover something that you are really like with in the process.
In the absence of this, do the experiments and tests to determine the best system and record everything on your paintings.
Also, sorry,  one other question you didnt really answer is:
 if a painting has significantly sunk in (hopefully I can stop this happening in future), is it ok to- once primarily dry, spray it with a couple of thin coats of retouching varnish and eventually a couple of thin coats of varnish. I assume if it is really sunk in it will bond with the varnish.. perhaps this is what will darken the painting significantly, if the varnish is bonding with the paint film itself? But I cant think about how else to protect the works. Normally, on top of a non sunk in painting, varnish still always carries a risk of darkening/yellowing, right? Even if it is winsor and newton and it states ‘non yellowing’.
I tend to discourage the use of varnishes early on as they are more likely to bond with the uncured paint layers. I do think that it is best to wait until the paint is cured and then apply varnish to even out sheen. The procedure you mention, however, would likely be fine as long as the varnish chosen for the process is made from a non-yellowing and readily reversible resin. Some of the modern synthetic varnish resins really remain non-yellowing or at least minimally yellowing for an extended period of time. Read more about this in our “Resources” sections on varnishes and retouch varnishes.
Thank you again for your time! 

Oh, and just to be clear and consistent. I recommend a fluid alkyd medium and NOT a gelled medium like Liquin (regular) to facilitate pourable oil paint.