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Shellac Sizing Test for Oil Paint on Paper

June 13, 2009

I wanted to demonstrate how effectively shellac performs as a sizing medium for painting oils on paper. The shellac mixture below was made about half a day before the demonstration was started.

Making shellac soap

Making shellac soap

This is de-waxed pale “blonde” shellac in the bag. I ground it down into a powder to help accelerate the dissolving process. I tend to make my shellac in a rather unorthodox manner than what is normally recommended by first making a “soap” using dissolved borax. That is how shellac based ink is made. It’s approximately 1 teaspoon borax, 8 tsp water, and 5 tsp shellac. I can’t tell you the exact amount since I tend to do it by sight these days instead of careful measure. I place this in a jar and set it on a coffee warmer while stirring for a few minutes until all the water is gone and I’m left with a paste that looks like light brown sugar (see below.)

Shellac mixed with borax

Shellac mixed with borax

Next I mix in grain alcohol. Most recommended mixtures just start with dry shellac and alcohol and avoid borax, which is perfectly fine, I just found that it takes longer that way and doesn’t give any better result. The alcohol I use is the Everclear brand which is 190 proof. Denatured alcohol would work fine, but also takes longer. Keeping the jar on the warmer, I occassionally stir the contents and after about 2 or 3 hours I get something that looks like creamed coffee. The amount of alcohol is again not precisely measured but roughly about the same as the “soap” volume I started with. It amounts to what is referred to as about a 3 pound cut of shellac to alcohol. I’ve also used a 2 pound cut, but I would want to add a primer layer to that. Acrylic primers adhere fine to shellac but I wouldn’t recommend thinning them with water.

Shellac on paper with different oils

Shellac on paper with different oils

Reflecting oil swatches

Reflecting oil swatches

The paper used here is thin bristol, about 90-100 pound weight. I’m using a thin paper so that any oil that penetrates through the shellac would be easy to see. I placed two coats of shellac on both sides of the sample paper and let that dry for about an hour. Next I placed three oil medium swatches of refined linseed oil, stand oil, and safflower that I had handy.

Oils on raw paper

Oils on raw paper

Back of painted paper

Back of painted paper

In the image on the left you can see the linseed oil and stand oil on a piece of the same paper that has no sizing protection, as well as a couple oil paints from Le Franc, red ochre and paynes grey, which I believe use safflower oil. The oils started to soak into the untreated paper immediately, and when you look through the back  (right image) you can see how the oils make the paper nearly translucent. As these oils dry they will release acid that will discolor the paper and likely make it brittle over time. Shellac prevents that.

All of these were made about 5 days ago. In the image below (looking at the paper from the back) you see how the shellac has held up after that period of time and the oils have dried. None of the oil has penetrated through to the back side of the shellac treated paper.

5 days later

5 days later

Shellac is excellent sizing protection for oils and paper as well as wood. I prefer it to other choices. It does take some time to prepare, but it doesn’t require the use of water that acrylic mediums or animal glues would need, so there’s no worry about wrinkled paper. Rabbit skin glue has to be made at least a day in advance, whereas this sheet was ready for painting from start to finish in about half a day. An acrylic medium would be faster to apply, but the paper has to dry completely, requires taping down the paper, and I just don’t like the feel of oil paint on acrylic. A batch of fresh shellac will last at least six months or more. I keep it in the fridge until needed.

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23 comments

  1. I read your notes and will agree with you, though I have a friend who paints like this, I dought that it will last 80-100 years as the shellac will crack over time on bendable bases as paper that do shange structure as they age.


  2. Thank you for your reply, Dimitris. I believe it is an exaggeration to say shellac “WILL” crack over time. If the paper is mounted to a firm inflexible support there will be no bending and very little movement, certainly no more than with wood panels or canvas. However, any future conservator repairs might be more trouble on paper than other surfaces. How well anything will last in 100 years is difficult to know.


  3. HI David,

    Thank you for posting this information and taking the time to post your test. I love painting on a shellac ground both on paper and on panel. If using a good rag paper I doubt cracking will really be an issue as the paper absorbs. Is there a real reason to make ones own shellac? Is store bought inferior?

    Also, while researching this topic, I came up with the following comment from someone else and I wonder if you have an answer for his claim:

    “To adhere properly, oil paint requires a surface that has tooth and absorbency. Protecting the surface with shellac, fixative, acrylic varnish or acrylic paint will protect the paper but will not provide a sympathetic ground. Norman Rockwell prepared many of his illustration boards with shellac before painting with oil in the 1920s. Now many of these paintings are in poor condition after only 80 years – a short time in the life of a painting.”

    Sometimes I have notice when working on wood that the paint scratches more easily, so I do wonder if perhaps there isn’t enough adhesion so I am experimenting using less shellac (one coat) so that the surface has more tooth. This appears to be working better.

    Thanks again,
    Mary


  4. Mary, some commercial brands of shellac have additives to extend their shelf-life, but without knowing what’s in it there’s no way of knowing what that will do to the painting. Fresh shellac is not difficult to make, and is much cheaper in the long run. There may be some places online that will make it up fresh for you.

    Metal plates have little to no tooth or absorbency, and old oil paintings on them are in excellent condition. Any number of factors can be related to the failure of a painting over time, including how well the materials are made, applied, or their quality.

    Have you sanded your shellac’d panels? A quick sanding with finegrit sandpaper can help give more tooth for the paint. One coat won’t likely be much of a barrier if you’re using 1-2 pound shellac.

    A lightfast test might show how well shellac will last. Place a small sample of quality paper sized with 2-3 coats of clear de-waxed shellac in a south-facing window for about 6-12 months, and see how well it holds up. You could also apply some oil paint to it to see how well that adheres.


    • Thanks for the info, I’ll try your recipe out.

      I agree, paintings do fall apart for several reasons and we must keep the conservators in business anyway! As long as it doesn’t flake off in my lifetime, so I’ll definitely try sanding.


  5. check for different qualities


  6. Shellac is the best sealer there is for porus surfaces. It will only disolve in alcohol and once dry, 20-25 minutes, is totally impervious to other solvents or oil. Shellac may be bought in spray cans or by the pint or quart. It is available as amber or blond. For paper it should be liberally thinned with denatured alcohol. Ten-twenty percent shellac should be fine. This is a lot easier and undoubtably better than what you are doing. To make shellac from shellac flakes place flakes in the toe of a stocking and suspend overnight in a tightly sealed jar of denatured alcohol. The stocking retains the impurities. Denatured alcohol is hydroscopic and absorbes moisture from the atmosphere so keep shellac tightly sealed.


    • Thanks for the reply, Robert. If you’re calling commercial shellac “undoubtably better,” you have no way of knowing that. I have plenty of room for doubt in pre-mixed shellac, and that’s the whole point. It’s possible whatever they add to it won’t be detrimental to my artwork. Without knowing everything that’s in it, I can’t say. When I make it myself I know it’s okay. As for being easier to use, I don’t consider dissolving the flakes in alcohol as difficult, and once it’s made it’s as easy to use as any commercial brand. There’s a cafe up the street from me that makes a decent omlette, but mine are better.


  7. I think he may be referring to the method of making the shellac…

    That does sound like a simple process using the flakes in a stocking. My question, what is the ratio of flakes to alchohol?


    • Mary, the shellac solution is described as a “pound cut,” meaning one pound of shellac diluted in one gallon of alcohol. Breaking that quanitity down to a more manageable size, I usually use a 2 pound cut which would be 2 ounces of flakes to 8 ounces of alcohol. If you’re using a metric system, you’re on your own, but it doesn’t really need to be that precise, and I’ve been making it up for so long I typically just go by sight rather than measuring.
      It’s also good to use de-waxed shellac flakes and get as light a color as possible for sizing the paper. The terms for the light color vary quite a bit from bleached, clear, white, extra blonde, etc. From what I’ve read, bleaching which can weaken the shellac somewhat, but makes it clearer.


  8. Thanks for the recipe. I have a supplier and plenty of denatured alcohol so I should be good to go. I do love the surface shellac provides!


  9. [...] to test that out. My preferred sizing for paper, which I’ve written about before, is actually shellac, but hide glue can work well [...]


  10. Hi David,
    Thanks very much for this article, just what I needed to know – if you don’t mind, here’s another question: Have you used ‘white’ shellac and how much does it tint the paper with yellow? Do you know of an almost colourless shellac? I’m a little sceptical of the claims so I thought I’d ask before I buy it.
    Thank you,
    Alberto


    • White or clear are both terms used for bleached shellac which is the clearest type you can get. From what I’ve read, bleaching can effect the long term durability. Another process uses solvents to lighten the tone, with names like extra or ultra pale. That’s the kind I prefer, and although it has a slight tint to it like weak tea, it’s not that noticeable in 2 coats.


      • Thanks again, I’ll ask about the bleaching process before I buy.

        Alberto


      • Hi all, Kate here. I am a furniture conservator and watercolor, gouache and acrylic painter who is just starting to use oils for paintings. That is how I ended up reading about grounds for oils.

        About shellac: bleaching is not done with traditional bleach, but it is a rendering process. It does not weaken the shellac’s life in furniture. Traditional shellac is easy to make, and we do not recommend using store bought due to additives. Use a good denatured alcohol for mix.


      • I’m not sure what you mean by “rendering process,” Kate. As I understand it, bleaching shellac involves dissolving it in an alkali solution of sodium carbonate and sodium hypochlorite. Sodium hypochlorite is bleach. I’ve read comments from various cabinet and violin makers who claim that the bleached version is weaker than one that is just filtered through solvent. It’s a statement that seems to make sense to me, but I have no specifics on that or if it makes that much difference in the long run. I have also tested bleached shellac and it seems to work fine. If I were only using it as a surface wood finish I wouldn’t care much, but as a foundation for paint I’m going with a non-bleached product.


  11. David, if you don’t mind, another question while I’m waiting for my shellac to arrive. I’ve been reading that it yellows or darkens considerably (even in the dark), after its first application. I’m wondering if this has a noticeable effect on the painted overlayers – i.e. darkening the whole painting. How long have you been using it, and have you noticed any darkening in your work?
    Thanks,
    Alberto


  12. My first exposure to shellac began about 15 years ago from a friend who repaired and built musical instruments. He made his own also. I later read about a landscape artist who was using it to size paper for her oil paintings (her name escapes me at the moment.) All that started me off on my own experiments and research.

    I had bought some premade commercial shellac once to test out and after about a year noticed it had turned considerably darker in the can. I can’t say it was the shellac itself that caused that since I don’t know what all they used to make it. Since then I’ve stuck with making my own.

    Shellac is a resin and in it’s pure form is rather dark, in some cases almost black. However, it can be processes to be nearly clear. If it’s not dewaxed that can also cause problems with paint. Waxes can darken over time also.

    For those who make claims against shellac, I’ve never seen any actual examples or test results, and what type of shellac they are talking about? Was it the commercial brand? Was it dewaxed or clear shellac? I need to see proof.

    I’ve heard similar claims against resins like dammar, but that’s when it’s used as a top varnish, which is not how I use shellac. As a size or isolation layer, it’s tempered with layers of paint and not exposed to UV rays. I’ve tested the shellac I’ve made just like I’ve tested my own paints, and it holds up well.

    Ultimately, it’s either take other people’s word for things or make your own tests. I tend to do a little of both.


    • Indeed, my sentiments exactly. I prepared some tests yesterday which I’ll complete with the shellac that’s in the mail. I’ll be observing it over time especially for yellowing/darkening under oil paint of varying thickness: transparent translucent and opaque, with two whites and cobalt blue. Of course I’ll be happy to share the results with anyone interested, so don’t hesitate to ask. Your experience is incouraging, thanks for the information.

      Alberto


    • Thanks for all the info on this technique, it’s just what I’m looking for. I would like to use oils on paper and have so far made no doubt fairly temporary paintings on large sheets of 300gsm paper by sizing only with oil based primer so to prevent buckling but I was aware that the oil may disintegrate the paper over time! I was wondering whether you had any thoughts on sizing paper first with shellac and then finishing with oil based primer as I’m looking for a whiter finish ? Any thoughts I’d be grateful thank you
      rebecca


      • I can’t think of any problems with using an oil primer over shellacked paper, rebecca. Handle it as you would if on any other surface. You should be able to find bleached papers that are brighter than any white primer; although, the shellac might knock down the tone a bit. There are colorants sold at wood shops (such as the Mixol brand) that can be mixed with the shellac itself, if you want to try that. If that gives you the brightness you want then you won’t have to wait on the primer to cure.


  13. [...] paper (it applies to canvas also) before painting on it with oils. One article dealt with using shellac and another with hide glue (aka Rabbit skin glue.) Here I would like to mention another option of [...]



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