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Old 28-05-12, 07:13 PM
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Koo Schadler Koo Schadler is offline
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Default Tempera, Shellac, Oil

My usual working method is to develop an ET painting in depth - get the work around 99% complete in tempera alone. Then I isolate the ET with a thin layer of shellac; next I do several layers of oil glazes to saturate things, deepen the darks, get a bit more atmosphere in the work.

Although I've checked with various technical smarty pants (conservators and the like) who say the thin layer of shellac I use is not harmful, I'd like to get rid of it. The simpler a method, the better, I think - and I've had several painters speak critically of that layer of shellac. So, in the spirit of experimentation, I recently finished an ET, let it sit for 3 months to cure, then dove in directly with the oil glazes (thinking that on a ET surface that has cured and polymerized for several month the oil wouldn't sink in). Not so. Its that super absorbent true gesso, I believe - it keeps sucking dry my oil paint of its medium. Things drag, the surface dries uneven and matte.

So, I think I can still go ahead and put a thin, isolating layer of shellac on top (of what is now an ET and oil glazed surface) - any thoughts on this idea (i.e. shellac atop oil)? Someone also told me recently that shellac can't breathe, it fully seals the surface, but I think it is hydroscopic which makes me think it can breathe, yes?

FYI - I use a bleached shellac in a ratio of 1 part shellac to 6 or 8 parts denatured alcohol. There is no yellowing (I've got a 14 year old test strip that hasn't yellowed) and its on a panel (so brittleness shouldn't be a factor). Any other thoughts on shellac, and why it is so often dis'ed?

Koo
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Old 28-05-12, 10:45 PM
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Salamander Salamander is offline
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just a thougth Koo, couldn't you skip the shellac by oiling in your entire painting and paint into it as a "couch". thus keeping an oil layer below the paint glaze to be absorbed by the gesso?
I'm not sure that those old masters" that used et as an underpainting ever isolated it.
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Old 29-05-12, 12:46 AM
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Hey Koo, Have you ever used egg as a final "varnish" for oils? I'm wondering if it would impart that nice sheen....
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Old 29-05-12, 02:15 PM
dbclemons dbclemons is offline
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Quote:
Originally Posted by Koo Schadler View Post
...So, I think I can still go ahead and put a thin, isolating layer of shellac on top (of what is now an ET and oil glazed surface) - any thoughts on this idea (i.e. shellac atop oil)? Someone also told me recently that shellac can't breathe, it fully seals the surface, but I think it is hydroscopic which makes me think it can breathe, yes?

...Any other thoughts on shellac, and why it is so often dis'ed?
Shellac over an oil surface is not a problem, provided the oil has dried sufficiently, but not necessarily cured completely. Shellac is often recommended on wood surfaces that have a tung oil finish or the like to offer some surface protection to the furniture. When you're using a 1 -2# cut of shellac (which is roughly what you're using now) you shouldn't have a problem with the oil being able to continue to cure. This is how a retouch varnish works over a semi-dry oil painting. If you had applied a full strength varnish the oil would have problems.

Yes, shellac is hygroscopic but oil is not, so it will create a moisture proof barrier if it's used on top of the shellac. You could also combine the oil with the shellac in one step.

You might try to skip the shellac step with what is often referred to as a "painting medium." This is a mix of linseed oil, a resin, and often a drier is added. Most artist paint manufacturers make them, like Winsor & Newton. They are mainly designed for an "oiling out" technique to create an even sheen prior to final varnishing. I've never used it on anything other than oil, but it should work on dried tempera. Rub a thin layer of it over the surface. You can also make your own with 1 part linseed stand oil, 1 part damar varnish, 5 parts turpentine. Other resins you can try are Canadian balsam or Venice turpentine.

http://www.dickblick.com/products/wi...inting-medium/
http://www.youtube.com/watch?v=_SJbonZ1RhY

Thoughts on shellac dissing: although shellac is a natural organic material, it's manufactured and not a generic product. Even the raw flakes you buy are processed, and can have different amounts of wax or color. If you buy the commercial version (such as Zinsser,) there's no way to know exactly what's in it. When problem examples are cited, no details are given as to what type of shellac was used, where it came from, or how it was made or applied. Most of problems such as cracking or discoloring are due to the wax content. Use a couple layers of thin, clear, dewaxed, good quality shellac and you'll be fine.
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Old 07-06-12, 11:51 AM
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Koo Schadler Koo Schadler is offline
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Thanks Salamander and DB for your posts. I would like to do what you suggest - apply a thin layer of oil or oil medium on top of the tempera, so I can skip the shellac layer - but so far it has not worked. I've tried applying a drying oil on top (as you say Salamander) as well as DB's suggestion of various mediums (drying oils - walnut, linseed, sun thickened linseed - combined with damar and thinner) but so far everything I've tried has sunk unevenly into the tempera below it - in fact most of the oil and mediums have virtually disappeared into the painting! And they have taken anywhere from 1 to 3 weeks to dry (in fact some are still slightly tacky). This is true for both new tempera paintings (a week old) as well as pieces that have cured for several months (which I would think would be less absorbent, but they don't seem to be). I am surprised by how absorbent the surfaces are...but they seem to be very much so, and nothing seems to seal or isolate them as well as a shellac layer. Once I have the shellac on top, then I can oil out, and it works. So I guess I'll stick with that.

Your shellac info is very helpful DB - thanks. One more question - if something is hygroscopic, as in it can absorb water, does that mean it also allows air to pass through it, i.e. it can "breath"? I take from what you said that a relatively thinned shellac mix can, but if applied to heavily it can not breath, yes?

Thanks!

Koo

Last edited by Koo Schadler; 07-06-12 at 11:57 AM.
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Old 07-06-12, 11:56 AM
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Koo Schadler Koo Schadler is offline
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PS....In regards to your question Salamander, I don't think egg would work as a varnish for oil - egg is water based, not as strong a binder as oil, so its not suitable to sit on top of oil. I have tried different wax mediums on top of oil, and once buffed they cut a bit on the "gloss" of oil and give a finish that is a bit more akin to a tempera. I find a beeswax based wax medium (such as Gamblin's) does so better than a petroleum based wax (like Renaissance Wax) - the latter tend to be a bit more shiny (never mind the petro fumes).

Koo
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Old 07-06-12, 01:06 PM
dbclemons dbclemons is offline
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I'm not certain whether or not air can pass through dried shellc, since I don't know of any studies on that, but I sincerely doubt it. After it is dissolved it reforms into a single hardened sheet. Under high magnification this looks like a honeycomb of solid flat shingles, which accounts for its brittleness. I don't see how air could pass through. This is why it's such an effective finishing sealer, and the surface must be scuffed or sanded for anything to be applied over it. It's conceiveable that if the shellac were very thin then air might penetrate, since the shellac would be more dispersed.

Here's a magnified image of shellac over a machine coated (MFC) sheet of paper. You can see how solid the layer is.
http://www.springerimages.com/Images...0-010-9408-8-3
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Old 07-06-12, 01:57 PM
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Spirit varnishes were and are used as isolating layers in oil painting. Spirit varnish= shellac.
A good source for information and shellac supplies:http://www.shellac.net/index.html

Koo, as you're doing a mixed media, continue to use the shellac, as it works. Shellac is dissed because commercial shellacs, can and do "go bad", but the kind you're using should not be a problem. If you want to be absolutely sure, the alcohol is a problem area; you want the highest ethyl alcohol content you can find. This will require checking the MSDS each time, because the manufactures routinely change formula. Sunnyside used to be great, now not so. 90-95% ethyl.

No surface coating is completely impermeable, and though shellac is an excellent sealant, I doubt a thin layer is going to create problems with the underlying ET. The permeability of coatings is a subject that has come up as regards conservation framing, and the consensus, from conservators to conservation framing experts, is that surface coatings are NOT impermeable. So, the poor little eggs will be able to breathe, if they need to. (Actually, continue drying, and any off gassing from other materials, as most inanimate materials don't need to breathe.)

The second post down on my blob has some thoughts on shellac.

A few more thoughts. Shellac doesn't chemically change from drying, solvent release, and so remains solvable. You might detail your working procedure, a note on the back, for future conservators, or smarty-pants, because alcohol can be used as a cleaning solvent. Some conservators use shellac as a binder, for retouch colors, because of that resolvability.

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Last edited by Bron; 07-06-12 at 02:57 PM.
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  #9  
Old 08-06-12, 11:43 AM
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Koo Schadler Koo Schadler is offline
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All of that is really helpful - thanks guys!! I've always liked working with shellac but have had a few traditional, academically trained artists say I was nuts to use it. I feel better.

Koo
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  #10  
Old 08-06-12, 12:54 PM
dbclemons dbclemons is offline
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Quote:
Originally Posted by Bron View Post
...Shellac doesn't chemically change from drying, solvent release, and so remains solvable...
While this is true of shellac by itself, when oil is involved it will cross-link polymers as it cures and you'd have to use an extremely strong solvent like xylene to remove it. French polish finishes, sometimes used for flooring, have this characteristic. The most effective way to remove it is by sanding.
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