Paraloid B72

I will put thoughts below in bold, based on working with Andrew Wyeth on his temperas for the last twelve years of his life, and then another 11 years after his death.
I am planning to use Paraloid B72 on Egg tempera and i have some questions since it will be the first time i will be using it. I am planning to use it on icons painted with fairly high egg yolk content.
1. What percentage should be used for preparing B72 for this kind of paintings?  I use 4% in xylene.
2. I have read that there are multiple solvents that can be used. Does the polarity of the solvent affect the paintings?.
I don’t think polarity of the varnish solvent has any effect; the solvent evaporates.  But you don’t want to soften the tempera paint.
Someone mentioned that non polar solvents have a tendency to cause Fatty acid migration/ foggy spots on paintings.
Fatty acids — stearic and palmitic acids– are exuded BY the egg tempera paint.  Non-polar solvents (such as ShellSol D-38)  are especially useful at REMOVING the fatty (waxy) powdery white efflorescence.  (At one point AW used some tempera paint on a watercolor– and ONLY that area effloresced — it is strictly from the egg medium and is cut down by the presence of a coating)
This was mentioned for varnishes that sink into the paintings. How does this apply to the isolation layer produced by B72. I am between using acetone or ethanol.
You should use a dilute coat– AW hated shine on his paintings (he wanted a “dry” or “mummy” surface on his tempera paintings) but you might want shine?  Then you might use 10% or so, and it would cause a coating on the surface.
In my experience a 4% B-72 sinks into the tempera and is not evident at all as a coating on the surface– this pleased him.  But a 4% B-72 coating cuts down tremendously on the occurrence of future fatty acid efflorescence.
3. What will be the effects of sealing the paintings if they haven’t cured for over a period of 3 months? For example a period between one to two weeks..
I would not put any coating on a fresh, young tempera — wait at least 6 months.  The egg tempera would, I’m guessing, become readily soluble in whatever B-72 is soluble in if you coat it while it’s fresh (xylene, toluene, acetone, ethanol, etc.)  “Sealing” is probably not an accurate term unless you use a really thick solution — like 15-20%  [Which AW would have hated.  Sometimes dealers varnished his works without his permission, and he was quite unhappy with that.  And they used dammar or mastic which turned brownish yellow!]  But this should be decided upon according to the artist’s preference–no?
Thank you
Joyce Hill Stoner, PhD
Edward F. and Elizabeth Goodman Rosenberg Professor of  Material Culture, University of Delaware
Paintings Conservator  Winterthur/UD Program in Art Conservation

Director, UD Preservation Studies Doctoral Program

Dr. Stoner is a hard act to follow, but as a long time tempera painter I’ll add a few thoughts.
You’re probably aware of this, but xylene’s vapors are strong and noxious, so use with care.  Joyce has the advantage of lots of experience and a great spray booth; even with those advantages, I suspect she holds her breath every time she varnishes a Wyeth!   The point is that varnishing/isolating take considerable experience to do well, particularly with a relatively fast drying coating (although B-72 in xylene dries more slowly than when dissolved in acetone or ethanol).  Practice a lot!  I’ve known many artists who varnished for the first time on a cherished image and regreted their inexperience.  Tempera is a slow medium and it can be hard to accumulate “practice” panels; one solution is to apply leftover paint, at the end of a painting session, to a few small panels to build up practice surfaces.

Some aerosol cans of artists’ picture varnish are actually B72 (last I heard, Lascaux Fixativ & Varnish and Krylon Crystal Clear Coating among them).  Formulations often change, contact the company to be sure.  Spray application may seem preferable to using a brush, but even spray cans require practice to get right (i.e. consistent, no drips). Several thin coats are preferable to a few heavy coats, as “orange peel” (rough alligator skin) can appear if sprayed too thickly.  Don’t work too close to the surface or apply too slowly (can lead to orange peel) but don’t work too far away or too quickly either (creates inconsistent application).  In short, once again – practice!  
Ideally, I agree it’s best to wait for tempera to polymerize – 3 months minimum (I’ve found tempera to be generally insoluble at that point).  But not all working artists can afford to wait that long.  I’ve applied isolators (shellac and B-72) much more quickly (within weeks or, I confess, days) with no dissolving of the paint.  However coatings on uncured tempera tend to sink in more and can appear uneven.  I finish with a wax medium which helps to counter unevenness.  
I’ve isolated/varnished hundreds of tempera paintings and so far haven’t seen fatty acid efflorescence on my work – perhaps because I am tempering perfectly every time?  Well, more likely because coatings do seem to suppress the issue.  Many years ago Ross Merrill (former head of conservation at the National Gallery DC) warned me that “Alcohol…used on the painted surface of a tempera painting [to clean it]…may draw some of the components of the egg yolk medium to the surface, such as the fatty acids in the paint medium.  In oil paint (and I’ll assume in egg yolk tempera paints) some of these fatty acids remain essentially unchanged, and function as a lubricant or plasticizer to keep the paint elastic.  Drawing them out of the film embrittles the paint film.”  This isn’t the same issue as efflorescence, nor was Ross referring specifically to isolators/varnishes (rather to the issue of cleaning the surface of a tempera painting); still, I wonder if Brian and Joyce agree with this point?

Koo

Egg tempera artists are rarely prolific since it’s a slow medium; so there’s constant pressure to produce and get work out into the world – I’m sympathetic.

To correctly temper and varnish egg tempera, it’s important to understand PVC, pigment volume concentrate. It’s been discussed previously on this forum (enter into search engine), I’ll try to keep it simple.  Basically every paint has an ideal ratio of pigment to binder (it varies among binders and, to varying degrees, among pigments).  For egg tempera, the ratio is approximately 1 part pigment : 1 part binder (with minor differences among a few colors, a subtlety we needn’t address for now).  Most people add a percentage of water to yolk to make egg yolk medium; many people work with pigment pastes that have a percentage of water.  So, to temper properly, you have to mentally subtract out whatever water is added to medium and/or pigment pastes to achieve the correct ratio of 1 part pigment : 1 part egg yolk.  This sounds mysterious and daunting to newcomers, but experienced tempera painters know the feel/behavior of properly tempered paint and, with practice, good tempering becomes second nature.
Once paint is properly tempered, you can use as is (consistency of light to heavy cream, depending on your egg yolk medium) or add water (thin to consistency of milk or watercolor).  Whatever water is added evaporates away, leaving behind the correct ratio of pigment to binder.  As long as paint is tempered correctly at the start, the consistency can be altered by adding any percentage of water. This is why you see tempera artists working with thick paint, thin paint, and everything in between.
An under tempered paint has too little yolk – it tends to dry chalky, not adhere well, create dust, smear.  An overtempered paint has too much yolk – it tends to feel greasy and slippery, layers are hard to build up, may eventually crack.  While you needn’t get the ratio absolutely perfect, you want to be in the ballpark (more or less a 1:1 ratio) to create well behaved paint and good adhesion. 
As the painting coheres over time, an over tempered paint naturally expresses to the surface excess lipids; this is “fatty acid migration” (FAM).   Other factors can play a part in FAM (i.e. artwork which moves between dry and humid environment seems prone), but fundamentally I think FAM results from too much binder in the paint. This is why I joked that the lack of FAM in my work must indicate that I temper perfectly each time (when, in fact, it’s probably because I varnish, which is thought to suppress FAM).  
From what I hear, some Wyeth paintings show FAM – which isn’t necessarily a surprise.  Seeing his work in person I’ve noted varying degrees of shine on the surface: slightly over tempered in parts, a whisper under tempered in others – not enough to jeopardize the paint but enough to create slightly uneven finishes and, perhaps, occasionally FAM.  At least, that is my understanding (please correct me, Brian or Joyce, if I am oversimplifying). 
Some icon traditions encourage the application of regular “nourishing layers”; i.e. thinned washes of egg yolk medium.  Nourishing layers are initially gratifying (because they re-saturate and intensify values and colors, like a varnish).  But there isn’t a need for them (unless previous paint layers are very under tempered) and they throw off the correct ratio of pigment to binder, injecting unnecessary fats into the paint layers (which can eventually create problems like cracking or FAM). So you don’t want to work with an “egg rich” paint (as you’ve described it to me); you want a “properly tempered” paint. 

Okay, now onto varnishing. One of the characteristics of egg tempera is that it’s correct ratio of pigment to binder (or critical PVC) yields a paint with a very high percentage of pigment (a high solid content).  In fact, there is so much pigment relative to binder that pigment particles protrude above the surface of the paint film to create an irregular, porous, open surface.  I’d like to insert an illustration here, but not sure how to do it…Brian, help? (or the questioner, who I know, can email me).

This irregularity creates the matte appearance of egg tempera.  Varnishing fills in the porosity and smooths the surface, which increases saturation and shine.  

When a varnish is applied directly atop an irregular, porous egg tempera painting, the varnish sinks into that porosity.  This is why varnishes on egg tempera can appear uneven and may take a long time to dry (coatings that dry via oxygen aren’t well exposed).  A coating directly on egg tempera also becomes nearly inextricably part of the painting (it doesn’t sit on top of the paint film, but sinks into/meshes with it).  
One solution to these challenge is to first apply an “isolating” layer to egg tempera – a thin coating that dries quickly through evaporation of its solvent, and thus doesn’t have a lot of time to sink into tempera’s porosity. Then, on top of this “isolator” a painter could (if desired) apply another coating, for more protection or to control  shine.  

For example, I first “isolate” my temperas with either shellac (a controversial choice discussed in other posts) or B-72; then I finish with “wax medium” (wax, solvent and synthetic resin; there are many commercially produced wax mediums such as Natural Pigments, Gamblin, Grumbacher, Renaissance Wax).  The isolating layer protects the painting; it also allows me to apply wax medium before the tempera has fully cured (the mechanical action of rubbing on wax can smear an uncured tempera).  Wax medium creates a softer, more organic finish that I prefer to the isolator finish (and adds a bit more protection).  

While the natural finish of egg tempera is matte, isolating/varnishing allows for any degree of saturation and shine. Many tempera artist object to altering the natural tempera finish but, as Dr. Stoner notes, it’s really up to the artist (nevermind that icons have been varnished for centuries; and many [pretty much all?] the Renaissance temperas we see in museums have, at this point, been varnished). 

I am skeptical about mixing varnish into paint – each dries at different rates through different means; I think the varnish could interfere with the polymerization of egg yolk into a stable paint film.  But I am not a conservator – Joyce or Brian better address this question.  It is possible to add a drying oil or resin (synthetic or natural) to egg tempera, to create a tempera grassa paint – but that’s a whole other topic and I’ve already gone on too long.
Koo Schadler

koo.pngkoo.pdf
Koo, if you email me the image, I can post if for you.
As to nourishing layers, they are probably a source of abundant free fatty acids. Such layers probably greatly exacerbate efflorescence. Varnishes seem to slow or stop efflorescence.
BTW Wow this thread really took off today.

​Koo, I I have uploaded the image. BTW, our IT person has fixed the problem and you can again upload images if you wish.

​Perfect!  Thanks Brian, illustrations are very helpful, especilly to visual people like artists!

You are asking good questions. Yes, the B-72 can be considered an “isolator”, on top of which you can apply another coating, or “final varnish”.  Why add a final varnish?  It’s an additional layer of protection; it’s removable (since it’s separated from the painting by the isolating layer of B-72) if future conservation is necessary (i.e. the final varnish ages, or the surface is damaged, dirtied); and a final varnish allows for control of the painting’s finish (satin, semi-gloss, gloss, high gloss, depending on the varnish and/or additives within the varnish).  Any varnish that goes on oil painting (and probably on acrylic, too) would work; there are so many options it’s impossible for me to address them all (never mind that I’m experienced in only a few).  So you need to look into what sort of varnish you want (solvent, drying time, finish, etc.) and, once again…practice!  
You are right to ask about solvent: you must be sure that the varnish you apply on top does not share a solvent with B-72, or you will dissolve the B-72 isolator as you apply the varnish.  B-72 has many solvents (ethanol, acetone, toluene, xylene) but most oil paint varnishes are not soluble in those solvents; most oil varnishes are soluble in mineral spirits (either odorless, called OMS; or full strength, called by many names depending on formulation such as white spirits, Stoddard solvent, paint thinner) or turpentine.  I’m not an oil paint varnish or solvent expert by any means, so if you have questions in this regard best to ask another moderator.
I’m much more experienced with shellac as an isolator and am in the process of transitioning to B-72 (I need more practice with it).  In my limited experience with B-72, I’ve found I need a slightly stronger formulation (maybe 6-8% solution; I’m still experimenting…) to sufficiently isolate the egg tempera so that the varnish (in my case, a wax medium) sits evenly on top.  There are different influencing factors to consider: how much tempera paint have you built up (an isolator may sink in more on thicker paint layers); how long has the egg tempera polymerized or cured (isolator sinks in less the longer the painting has cured); how you apply the B-72 (via spray or brush on, as each deposits different amounts of isolator – I don’t have a spray booth so I use a sponge brush); what your final varnish is (for example, a pasty wax medium doesn’t sink in to the same degree as a liquid varnish) – and so on.  You’ll need to experiment.  Aim for the thinnest possible solution that isolates the painting sufficiently to allow for an even application of the final varnish. 
You could also apply nothing on top of the B-72.  Then, in a sense, your isolator becomes, by default, a sort of final varnish.  It’s not as protective, but certainly more protective than nothing.  
If you’re wondering about the uncertainties of this process I think it’s mostly because there aren’t many tempera artists to begin with, and only a very small portion of those who varnish (and mostly they are icon painters using olifa, which I believe nearly all conservators would agree is a terrible varnish).  There’s not much commercial incentive to figure out the process because the market is incredibly small (although there are some generous people in the industry – George O’Hanlon and Sarah Sands come to mind – helping tempera artists with the process).  So how to effectively, responsibly varnish contemporary egg tempera paintings is still somewhat uncharted waters.  Yes, Dr. Stoner has figured it out beautifully for Wyeth’s work, and offers an excellent starting point….but more needs to be understood for artists who have expectations, circumstances different from Wyeth. 
Please let us know how it works out. 
Koo

​​Thanks so much for reporting your experiments so far – very interesting.   
I don’t know what that “whitening” is.  I have not seen it on my own paintings (although most of my work is in other’s hands, so who knows….).  I did see it appear, after a year or so, on some varnish and isolator test panels.  I can’t discern a predictable pattern, what might be instigating it; the whitening appears in varying amounts (from very minimal to a lot) on perhaps 5% of different test panels (most pronounced on paint samples with Laropal A1 as an isolator + wax medium on top).  See attached image, one portion of one test panel.   Varnish Panel, Whitening.jpeg   It’s a bit hard to understand my notations, I’m including the image primarily to show the whitening.  Is this what you’re seeing?

This whitening looks akin to fatty acid efflorescence on tempera, so perhaps one explanation is that some isolators and/or varnishes (or their solvent) draw lipids up to the surface (which are then, unfortunately, trapped under the isolator or varnish, and can’t be wiped away, as fatty acid efflorescence generally can be).  Or, maybe it’s salts/minerals within certain pigments being drawn to the surface? I continually dry out and then rehydrate my pigment pastes, and sometimes this draws a powdery whiteness to the surface of some colors; whatever this is that occassionally effloresces on some of my pigment pastes also looks a bit like this whitening.  
But this is all speculation…I don’t know what the whitening is.  Any thoughts from Brian, Joyce, George?
While the thinking is that isolating and/or varnishing may surpress efflorescence, perhaps in some instances isolating/varnishing can instigate and/or trap efforescence. This is pretty much my nightmare scenario regarding varnishing egg tempera!  It would be great to understand it better….
Koo

Koo
I can’t tell for sure from the image but the “whitening” on your panel seems to be associated with the application of wax. We commonly see efflorescence on wax surfaces. Wax contains plenty of free fatty acids.
In my experience, this defect usually comes from a few different mechanisms. Fatty acid efflorescence which can usually be wiped away if treated soon after its appearance. A similar effect can be seen if a varnish is applied in a too fast drying solvent like acetone. In conservation we call this defect “bloom.” The rapid evaporation causes a cooling of the surface below the dew point causing a precipitation of water. The water can then be trapped in the surface coating creating a haze. This is a varnish defect and could be remedied by removing the varnish. This also why it has always been recommended to only varnish of relatively dry days where there is little moisture in the air.
Finally, there is blanching where the actual paint has fissure and minute pockets which scatter the light. This is almost always caused by overzealous cleaning by poorly trained restorers. It could also happen if the artwork is stored in a very hot, overly dry environment and becomes desiccated. The application of an additional varnish layer can sometimes remedy this.
BTW, I do not think that Joyce monitors this forum as regularly as we do (she is super busy) I will email her a link to the topic again.

​I was just reviewing an email conversation I had many years ago with Alan Phenix (former conservator at the Getty) in which he notes that much of the fatty material in egg yolk probably remains mobile after the paint has dried (unlike the lipids in oil paint, which are drying oils).  So, egg tempera paint, when over-tempered with too much yolk (or, perhaps, even when perfectly tempered?) seems always, potentially, vulnerable to lipids traveling up to the surface; perhaps instigated by changes in humidity (as Joyce notes) or perhaps by solvent action on the paint surface?  Perhaps the reason some isolators and/or varnishes inhibit lipid efforescene (as Dr. Stoner sees on Wyeth’s temperas coated with B-72) is because the isolator/varnish sinks into the porosity of an egg tempera paint film and sort of “freezes” the lipids in place?  Just speculating, trying to understand… Koo

That is certainly true. What also seems to be the case is that a varnish slows or eliminated them from coming to the surface.

​​I appreciate Joyce is very busy and am glad she chimes in when she can.  The whitening on my test panels is definitely most pronounced under the wax finishes, but is also present elsewhere, under other finishes; and unfortunately none can be wiped off, all are “trapped” under the isolator/varnish on top….  In all instances the whitening appeared several months or years after the isolator/varnish was applied – I don’t fully understand what’s going on.   
Good to mention the importance of isolating/varnishing on dry days.   The original questioner might consider having a hygrometer in his studio, to be sure relative humidity is low.  I aim for 60% or less RH when isolating/varnishing; what do conservators recommend?