Paraloid B72

I am not sure that an exact number is stated but the closer to 50%, the better. 60% is probably totally fine.

​I believe at one time, Koo and I speculated that the whitening under the varnish was due to lipids in the egg yolk dissolved in the non-polar solvents and rose to the surface as the solvent evaporated. Correct me if I am wrong, Koo, but this speculation arose because Koo did not observe in paintings isolated with polyvinyl acetate dissolved in acetone. This, however, would not explain why this occurs much later, but likely relatively soon after the varnish is applied. Of course, lipids are also soluble in polar solvents, so this may not be a valid argument either.

​Yes, George – you are correct, that was our thinking, and it still makes sense to me.  However, as you note, it doesn’t explain why whitening appears later and/or increases over time.  
I think the whitening we’re seeing are lipids, which remain ever mobile in egg tempera, rising up the surface.  The mystery is what causes them to effloresce.  Humidity, as Joyce notes, could well be a factor.  The primary questions I would like answered are….
1.  Are there other factors that might cause lipids to migrate up to the surface?

2.  Is the primary cause over tempering (too much yolk in the paint relative to pigment)?
3.  Or, because lipids stay ever mobile in ET, could even a properly tempered paint potentially experience lipid efflorescence under adverse circumstances (humidity changes, or whatever else may  cause it)?

4.  What isolators/varnishes lock the lipids in place?   And do they do so permanently?

I realize there may not be answers to these questions at this point – just a wish list. (-:

Tempera paint quickly dries to the touch via evaporation of its water content – but drying isn’t quite the same thing as polymerizing (i.e. “to form a polymer”).  Egg yolk polymerization is a complicated (and not fully understood) process.  Here’s how I understand it, and hopefully more scientifically trained moderators will clarify where needed.  
Egg yolk contains (approximate amounts):
water                          50%
egg oil (lipids, fats)       30% 
proteins                       15%
other ingredients          5%  (the most important being lecithin, an emulsifier that enables egg oil to stay suspended within its watery base). 
Egg oil is generally considered a “non-drying” oil (versus, for example, drying oils used in oil paint such as linseed, safflower, walnut, poppy).  The degree to which egg oil does or does not polymerize is one of it’s mysteries… 
Egg proteins are made of tightly folded molecular strands, held together by weak bonds; when subject to heat, sunlight, and/or oxygen the bonds break and the strands unravel, then interconnect (cross link) to form a cohesive film.  In short: egg proteins create the paint film, egg oil contributes plasticity to the paint film. 
Heat is one way to break down the bonds to allow the protein strands to unravel, then reconnect (as seen in a cooked egg).  The drawback to heat as a “curing” agent is that it produces cloudiness.  This is most obvious in egg white (or “albumen”; not to be confused with water soluble proteins called albumin), which transforms from transparent to opaque when heated.  Of course tempera artists use the yolk (not egg white), and yolk doesn’t change as significantly; still, it does become more opaque when cooked.  How much this opacity visually impacts a paint film, I can’t say. I’ve been told that heat also adversely affects plasticity (I don’t know this for sure –yes or no, other moderators?).  In short, heat isn’t the best way to create an egg tempera paint film. 
Oxygen and light cure by evaporating the water content (in paint and yolk), which causes the proteins to unravel and then cross-link with each other (FYI, latex paints “cure” the same way).  The oxygen and ambient light in a studio are sufficient for this to occur.  
I’ve been told that actinic light rays (in sunlight) create the best egg tempera paint film, but I don’t know why this is so.  Obviously there are challenges to placing a painting in direct sunlight: earth pigments are pretty permanent but many organic colors are prone to fading, and excessive heat can cause cracking in paint and/or gesso.  So I don’t recommend direct sunlight… unless a painter needs to speed up cure time of initial, underlying paint layers.  In that case, you can place a painting in the sun for a few hours or more.  Don’t let the panel get hot to the touch, and protect the surface from weather and critters (cats, dogs, mice and insects are attracted to yolk and might nibble on your image).  
How long does it take for egg tempera to polymerize?  I haven’t found a consensus for how long it takes egg tempera to cure.  It varies depending on factors like number and thickness of paint layers, and drying conditions.  It’s common to see 6 to 12 months given, but I think those numbers may be superimposed onto tempera from oil painting.  Egg tempera has less binder than oil.  Tempera paint layers are a fraction of the depth of most oil paintings.  Its high PVC surface is more porous and open to light and oxygen.  For all these reasons it seems unlikely that a tempera painting needs a cure time equal to oil.  That logic, combined with many years practical experience, leads me to believe that tempera paint polymerizes within about 3 months.  However I don’t have a study to confirm this and often see longer cure times given.  
How do you know when tempera paint has polymerized?  Two common ways to test if oil paint has cured are (1) gently press a fingernail into the thickest part of the painting and if no mark is left, the paint is cured, and (2) carefully wipe a corner of the painting with a white rag wetted with a bit of odorless mineral spirits, and if no color shows up on the rag, the painting is cured.  Egg tempera paint layers are so thin and its PVC so high that the fingernail test doesn’t work; and mineral spirits aren’t the solvent for tempera.  Egg tempera needs its own tests for polymerization.  
One possibility is to dampen, with water, a white paper towel or rag and tentatively dab at a painting’s edge (that would be covered by a frame) to see if color comes up – do so with great care, of course!  Another way to identify polymerized tempera paint is to gently polish the surface: if there is a certain hardness to the surface (recognizable through experience), and no color shows up on the cloth, and a gentle buffing doesn’t mar the surface but instead pulls out a subtle shine, the surface is probably cured (additionally, when I try to work on a surface like this I find the paint slips, slides, and doesn’t adhere well – also signs of polymerization).  These tests, while not definitive, have been good indicators of a cured painting for me.
FYI…the following articles discuss egg yolk polymerization (be forewarrned, they are technically dense). Last time I checked they were available for free download from the internet: Alan Phenix, The composition and chemistry of eggs and egg tempera; and Jaap Boon, Sophie L. Peulve, Oscar F. van den Brink, Marc C.  Duursma and David Rainford et al., Molecular aspects of mobile and stationary phases in ageing tempera and oil paint films.  Both papers in: Early Italian Paintings, Techniques and Analysis: Proceedings of the Symposium held at the Stichting Restauratie Atelier Limburg, Maastricht, 9-10 October 1996. Maastricht: Limburg Conservation Institute, 1997.

​I want to clarify one more thing.  Many tempera artists, myself among them, use a hairdryer to speed up water evaporation (which begins polymerization).  I do not (and tell my student not to) use a hairdryer to heat up the panel to the point of cooking the egg.  When applying hairdryer air to a panel, I regularly feel the painting’s surface to make sure the temperature doesn’t go beyond modestly warm (certainly not hot, i.e. in the 150 degree range necessary to cook an egg).  

I have less experience with B-72 as a varnish and have asked for some comments form those that do. I would, however, like to mention that B-72 is not perfectly soluble in straight ethanol (or at least the 95% possible without resorting to very sophisticated methods of refining beyond distillation). Additionally, if one is using denatured alcohol, the other solvents added to make ethanol non-consumable may influence solubility. When I use B-72 it is usually dissolved in xylene for painted works. There are times when I may need it dissolved in acetone as an adhesive but certainly not to be applied over oil paint. I have used B-72 in an 8-1 mixture of ethanol-acetone and achieved a clear solution. You may want to experiment to see if this is viable.

B-72 is soluble in many things, as noted on its MSDS.  Ethyl alcohol is listed as one of its solvents, so not sure why it didn’t work – except, as Brian notes, the alcohol may not have been sufficiently pure.  I’ve had luck dissolving B-72 in acetone, Toluene, Xylene; none produced any foggy issues.  
If the problem was incomplete solubility, tempera’s high PVC surface might have exacerbated the issue – the dissolved, transparent portion of the B-72 would have sunk into tempera’s porous surface, while the undissolved, more opaque particles could have separated out and settled on top (for this same reason, matte varnishes directly atop ET cause cloudiness because the matting particles separate out).   
B72 is insoluble in White Spirit, so any varnish with that as it’s solvent would work on top.  I’ve opted, after isolating, to finish with a wax medium (Renaissance wax being my favorite, but I also like Gamblin’s and Dorland’s) – but they may not give the level of protection you’re looking for.  While I’ve played with several varnishes on demo panels, I don’t have enough experience to report on how well they work long term, and so I can’t be much help in that regard.  Thanks for checking in with the results of your experiments – there’s more to learn regarding varnishing egg tempera and it’s helpful to have others experimenting. 

Thanks for reporting back on your experiments.  Here are a few thoughts.
Foam Brush: Yes, it’s tricky to load a foam brush with enough but not too much liquid.  I’ve always used foam brushes to apply shellac (similar in quality/viscosity to B72) & have gotten pretty good at loading the brush – I would say it’s mostly a matter of felt experience.  After doing it enough times I now can feel, as I load and then hold the brush in my hand, when it has the correct amount.  So it might be just a matter of more practice and developing a sort of felt, muscle memory.
However…I have a new, thin, flat, synthetic filament varnish brush from Natural Pigments that I’m eager to try – it has a good feel to it and may work well with B72 (although, because it is more expensive than a disposable foam brush, will require cleaning to get repeated usage).  
“While experimenting i have noticed that sometimes the paint might bleach if drops of the solution remain longer at an area. I am guessing the acetone/ethanol solution is not very egg friendly.”  You are correct – acetone and alcohol are strong polar solvents and, from what I understand, can swell and weaken a paint film, and potentially draw out plasticizing components (i.e. egg oil).  So maybe what you are seeing are egg lipids being drawn to the surface (a sort of immediate Fatty Acid migration). Then again, maybe it’s something else – a sort of “blanching” (see National Gallery Technical Bulletin, Volume 4, 1980 “Some Observations on Blanching”).  It’s hard to say.
“Lascaux varnish seems to react with B72 and dissolves it…”  
At the time of this writing, lascaux varnish is B72; and, in a sprayable form, contains a large amount of solvent – so not surprising that the underlaying layers are dissolving.  You need to varnish atop with something that has a different solvent, such as water, as in the W&N Varnish. 
I’m wondering: did you have any problem getting a water-based coating to behave atop the B72? 

“Lefranc Bourgeois Vernis A Tableaux,Anti UV aerosol also reacted..i do not know why…it is suppose to contain Stoddard Solvent..which is white spirit based.” 
This is interesting to me because when I applied Renaissance Wax on top of B72, the cloth with which I applied the wax picked up a bit of color.   This meant either (1) my solution of B72 (1 part B72 to 15 parts acetone) hadn’t fully isolated the tempera, so the cloth was in touch with and abrading the surface of the painting, or (2) the Renaissance Wax, mineral spirit based, was affecting the underlying B72 isolating layer.  Given that mineral spirits are not the solvent for B72, I dismissed the second theory and presumed my isolating coat was, at a 1:15, too thin.  And this may still be the correct explanation of why I picked up some pigment.  But now that I hear you too experienced a top coat with mineral spirits affecting an underlying layer of B72, I’m wondering….

Varnishing contemporary egg temperas is complicated, and hard to resolve without more research and studies.  Depending on artists to do these studies isn’t ideal (we lack proper training, equipment, chemical expertise, resources and time – after all, we are compensated for painting, not research!) but so it goes in the obscure world of egg tempera.  I’m in the midst of rewriting the chapter in my book on varnishing egg tempera, and as always I’m somewhat flummoxed by the topic – each new approach seems to generate more questions.  I know Dr. Stoner has success when coating Wyeth’s painting with a thin solution of B72, and am very appreciative for her sharing her expertise.  (And the fact that she feels it’s worthwhile to apply B72 to Wyeth’s work seems to say something about egg tempera and varnishing…)  Still, the experience of a conservator working with professional equipment varnishing the well polymerized work of a single artist hasn’t yet translated into an effective working method for an ordinary ET painter in the studio, using a variety of materials and methods, varnishing recently completed paintings.  It’s still not clear how to do this properly or effectively.  
I don’t think it’s pointless or impossible to figure out. After all, anunvarnished egg tempera, with it’s absorbent, porous, irregular (i.e. vulnerable) high PVC surface presents challenges too!  Historically temperas were often varnished, albeit imperfectly (olifa being a good example) – and there will always be artists who want to varnish for the protection and saturation.  So I remain convinced this is a worthwhile puzzle to  solve… but for now I think it’s still a puzzle.  Your contribution is helpful and appreciated.
Koo

I thought that Lascaux varnish is water based,i remember that you mentioned that the spray contained B72 but i thought the liquid one was different,
Not, Lascaux’s varnish is not water-based. Spray varnishes are generally made from the same resin as a brush varnish; there’s just a lot more solvent in the spray varnish (which is what makes it spray-able – and also, by the way, more noxious; always use a respirator). 
i do see subtle whitening on their icons. 
It’s very hard, without seeing and studying this whitening, to say what it is.  Could be excess lipids migrating to the surface (fatty acid migration, FAM), or moisture trapped under a varnish, or some sort of mysterious blanching (as discussed in that NG bulletin I mentioned), or…who knows.  
I know quite a few icon painters who are enthusiastic about adding extra egg yolk to paint & glazes (thinking that egg yolk contributes luminosity – it does not) and to the paint surface via nourishing layers (which are generally unnecessary, unless a layer of paint is notably under tempered). Too much egg yolk isn’t good – contributes to various problems in the future, among them FAM.
Others tend to use more harsh varnishes like the floor varnish that i have tried or even varnishes based on white spirit ,used mainly for wood protection.
White spirits (mineral spirits) in a varnish isn’t necessary the problem.  It’s the resin and additives used in a floor varnish that are problematic; they are more apt to yellow (perhaps even intended to yellow, to warm/color a wood finish), and not made to last as long as artists materials (i.e. B72 remains colorless and soluble for up to 200 years potentially – I doubt whatever one buys at Home Depot can match that). 
Their works do not suffer much because i am guessing is due to the chemical nature of their pigment? I tend to use natural pigments and minerals. What are your thoughts on this? I mean there is the chemical part of the pigments and then the egg emulsion problem.
I’m not sure what exactly you mean by “suffer”, what specific problems you’re referring to… Artists have always worked with a variety of pigments: natural and synthesized, organic and inorganic – it’s fine to have this mix, as long as you’re using artists grade pigments. 
Problems sometimes appear if they build up their layers through glazing. Bleaching occurs.
Could be FAM, due to excess egg in the paint layers, as I mentioned above. 
Some russian iconpainters do something else. They saturate the layers of paint with olifa,or another oil. Remove the excess and leave the icons to fully dry up for a few days. They then varnish their icons.
Do you know specifically what oil they use, or if they add a dryer to the oil?  After isolating the icon with oil, what do they use as a varnish?
I very much admire the tradition of icon painting, and have many friends and students who are wonderful icon painters; but the tradition is, well, very traditional, and not all of its materials or methods are “best practices” (durable or safe ways to work, relative to current conservation science).  I think that most conservators would agree with me that Olifa is not a good varnish (slow drying, attracts dust, yellowing, not removable).  How soon problems show up, how much of a concern this is to the maker or owner of the artwork – well, these are complicated issues….  
Concerning the renaissance wax,i think that your layers were not thick enough to protect the paint. I have mentioned some experiments with various numbers of B72 layers. The thinnest ones did not provide any protection from the varnishes that were reacting with paint.( As a test for how many layers were needed for protection).
Yes, I think you’re correct, that it was too thin. I appreciate your feedback.
For the L&B aerosol varnish. I have spoken to someone and told me that the problem might have been that i didnt shake the spray enough and might have caused problems. I don’t know..i got confused because he also paints with  natural pigments and traditional egg emulsion and sprays his icons directly with no isolation etc. He does  this after 3 to 4 days and said that all is fine.
Everyone works differently – could be he paints in very thin layers, and/or on a less absorbent gesso, with faster drying umbers, has different expectations – without knowing all of the details (any one of which could be important), it’s hard to say why a practice works for one person and not another.  It’s true, spray varnishes need to be shaken very well, and take practice to apply consistently (don’t spray too close or slowly – you get orange peel; nor too fast or far away – you get inconsistent converage).  Might be a matter of more practice. 

I didn’t  quite understand your question on water based varnishes on top of B72? Do you mean if the surface produced is even ?
Often, when you apply a water-based substance atop a plastic-like, water-resistant coating (like B72), the substance beads up and won’t flow. So I wondered if you experienced any of that.  Did you work with the Artisan Water Mixable Gloss Varnish or the water based Galeria Varnish series?

” when I said icons suffer, i meant the bleaching problem ,but also the disappearing of very thin final glazes, and the disappearing of pigments that tend to be less concentrated than others. For example titanium white vs Antimony white. The latter tends to fade changing the overall tone of the icon.
I have heard of the problem of “disappearing” glazes (that are not fugitive pigments) from one other iconographer.  I haven’t experienced it and, unfortunately, have no idea what’s happening.  The only thing I can contribute is that I have seen egg tempera paintings affected by very high humidity –one example in which the top layer of a painting did seem to sort of “disappear” in parts, and the only unusual circumstance was a high RH environment for a couple of weeks.  But this was just a single experience, and I don’t know whether RH was specifically the problem, or if it relates to what you’re seeing. 
“I thought that natural pigments have a greater tendency to react. I have observed this with ochre and terra verde'”
Au contraire, natural earth pigments are among the more stable colors.  Could you clarify what you mean by “react”?   Conservators, any thoughts on this?

“Concerning FAM. Doesn’t it occur even if the pigments are correctly tempered?”
It seems logical that FAM would be exacerbated by an over tempered surface.  But yes, it’s also possible that FAM can happen in a properly tempered painting, depending on conditions: FAM seems to be less common in small panels, appear more often in large panels.  It’s believed to be exacerbated by high humidity but not contained by low humidity, and is not pigment dependent. FAM may be encouraged by less absorbent grounds (acrylic gesso) and non-absorbent supports (aluminum panels) because the porosity of traditional gesso ground and wood supports provide a home, so to speak, to mobile lipids; on less porous surfaces, excess lipids have nowhere to go except to the surface of a painting.   Isolating/varnishing egg tempera seems to suppress FAM.  As the italicized words indicate, much of this is speculative; I don’t know if there have been many, if any, studies on FAM in egg tempera (Brian or Kristin, do you know?).   
“Under tempering is not an option but i had a friend that used to paint like that. His icons felt chalky and were of course white, up to the varnishing point with olifa. After some time he told me that he tried an emulsion consisting of 1:0.5 egg yolk to varnish. I dont remember exactly what he was using.. if not mistaken it was damar varnish.  The person that advised me on the L&B varnish paints using concentrated paint mixtures,so in 3-4 layers he finishes the base layer of an icon. He also told me that lately he uses more egg in his mixtures because there is less effect from varnishing e.g Disappearing of pigment, and whitening..so i dont understand the FAM issue.”
Unfortunately it’s impossible to accurately assess these issues without seeing how a person actually makes/tempers his or her paint, or the paintings that results (and even then it would be difficult!)  I just can’t  know, from a distance, what ” less egg” in a mix actually means relative to how the person previously tempered.  Paintings are such complicated constructions, as are the environments in which they live….so it’s really hard, especially from a distance, to untangle the problem.  Wish I could be more helpful.  )-:   

“I tend to paint with glazes and thinner layers..i try using the 1:1 ratio after you have advised me ,so i do not understand what is happening. I tend to use more water to thin down the paint after the correct tempering of the pigment.”
Yes, once you have properly tempered a paint, you thin it with water, not more egg.  However, if you REALLY thin a paint with a LOT of water (until it looks more like rinse water than paint), you may want to add a touch more yolk, since at that point the binder is so dispersed.  With attentive practice, you can develop a feeling for when thinned paint is underbound and needs a drop more egg.  

This may be a bit of an awkward analogy, but a well-tempered surface feels a bit like healthy human skin – not too dry or chalky, not to greasy or sticky.   The main thing is to stay attentive and interested in tempering and the paint surface, and learn through experience and intuition how to temper properly.  Consistent, proper tempering solves a lot of problems (although not all; atmosphere and circumstances play their part too).  

​There is a small amount of solvent retention in B-72. This will lessen and evaporate over time. Many resins retain some solvent and release it as time goes on. Some of this has to do with the affinity of the solvent with the molecular structure of the resin. B-72 is routinely used on museum objects. We know that the film will become less rubbery and more solid over time. This is more of an issue when the B-72 is being used as an adhesive than as a surface coating where the “rubbery” quality could cause a join failure if it has not been allowed to offgas before applying strain. 

Sorry that I skipped this part of your question. No, there are no residual components of acetone that should be removed with isopropanol. The very concept makes no sense to me.

FIY, ethanol is retained for the shortest period of time from a film of B-72 as compared to other solvents. Acetone is close. I think that the primary consideration for this info is to realize that a surface may be minimally tacky for a period of time. The important take away would be to not wrap one’s artwork in a material that could stick, especially if exposed to elevated temperatures. Things like glassine or bubble wrap, etc. are really not appropriate as wrapping materials.
Other than this, I think that you are worrying too much. There should be no damage to a work that could initially receive a coating containing either ethanol or acetone. Keep in mind that these are very polar or at least high hydrogen bonding solvents and they can readily damage oil and acrylic paintings. Casein and egg tempera should be fine.
I am not sure what varnish you would put on top of the B-72. It is not uncommon to give an initial layer of a high molecular weight (MW) varnish like B-72 and follow that with a lower MW varnish like Regalrez, etc. The high MW would sort of isolate the surface while the low MW would provide the sheen and saturation (if that is desired). Even this is likely too fastidious for most situations and should only be attempted after much experimentation with mockups.  Most egg tempera painters do not wish for a super saturated surface effect. Others may as this is wholly an aesthetic consideration.
All resins retain the solvent for a period of time, how much and how long is particular to their molecular structure as stated and, of course, to the ambient temp/humidity. I would greatly caution against using a hot air gun to accelerate the process. Keeping the work in a warm, dry room may be advantageous for removing residual solvent but it is just as likely to cause problems in the substrate, sizing, ground, and paint layers. Best to leave that alone.
Sandarac yellows horribly (I have paint outs to prove it), it is best to just avoid it.
If you really want to go down the rabbit hole about B-72 and solvent retention, here is a very technical article of the subject:
https://heritagesciencejournal.springeropen.com/articles/10.1186/s40494-019-0283-9

Solvent evaporation and oxidation do occur through layers, it is just slowed down. This is more of an issue with oil paintings where the surface readily oxidizes and become hard while interior paint remains flexible. This does not mean that the interior oil layers will not oxidize, it is just that the surface can become brittle while the interior remains flexible causing drying cracks at the surface.
This is not really the same with aqueous systems where the paints become quite solid rather quickly (yes, they will become more brittle over time but not in the same manner as paints made from drying oils). 

I am not sure what is happening. It is also difficult to see what you are describing since I did not see what the surface looked like before the change. However, there is no physical possibility that the organic solvent acetone is bleached out the inorganic pigments you mention. I am not disputing that there has been some sort of blanching, bloom, or deplenishing of the surface binding layer that is causing a perceived lightening of the color. One can see a similar effect when you watch an underbound, aqueous paint layer dry. The color appears saturated when wet but grows lighter and lighter as it dries due to the paucity of binder and the exaggerate scattering of light. My guess is that the cause is either trapped moisture beneath the varnish layers or some form of disruption of the paint layer. There is no bleaching of colors like ochres and green earths. These are some of the most rock-solid colors that we possess. The transformation has to be a physical and not a chemical alteration. However, none of the above makes up for the fact that you are not happy with the appearance of your painting.
Just curious, how long was the paint left to dry before the varnish was applied?
PS Re-reading the thread I see mention of antimony white. Antimony tri oxide is quite poisonous, corrosive to one’s skin, and a carcinogen. This could be dealt with using good hygiene, but it also is darkened by hydrogen sulfide (let’s not forget the sulfur compounds in egg yolks). I do see its mention on a few icon painting related sites and that it can be imported from Russia for such purpose. It is true that zinc white is often added to surmount this problem, but I cannot think of a good reason to use that pigment in tempera. Perhaps there are virtues that I am unaware of.