Shellac and Linseed Oil Finishes

      A long thread on traditional finishes using linseed oil and shellac. May 28, 2010

Question
Recently I read an article about a finish using boiled linseed oil and shellac. The problem is the shellac is drying within seconds. It tacks ups almost immediately. This is my first experience with shellac. I doubt this is normal. Does it have a shelf life? I bought it at a lumberyard and it was manufactured 11/24/08. Is there something I can add to retard the drying? The can directions are worthless.

Forum Responses
(Finishing Forum)
From contributor D:
Give us a bit of a history into what you are finishing and why you chose this product. Shellac has been around for a long time, has many benefits, but also presents some challenges, which you are now learning about. Are you spraying or brushing? Have you tried other products or is this your maiden voyage into finishing? There may be better alternatives to what you are using. To begin with, shellac has a denatured alcohol base, so you could try adding more denatured alcohol to extend the working time (it isn't an extender, but a reducer, but it may help).



From the original questioner:
I generally just apply poly, but thought I'd give this a shot. I apply it using cloth rags, lint free of course. I did find that if I put it on heavier, it was a little more forgiving. I am starting by applying it to a small project, a pencil box. By applying it heavier I find that it pools in the corners easily. Not a good thing. With poly I have time to even that out, and thinning the poly helps cure that issue.


From contributor E:
Historically, varnish is linseed oil and shellac boiled together. The shellac makes the linseed oil dry hard and the linseed oil makes the mixture alcohol proof. Varnish cannot be re-dissolved in any solvent, but it can be removed with paint stripper. SPAR varnish is by and large linseed oil with a bit of shellac which makes the mixture remain soft and flexible for outdoor use, but not good for interior use. Seems that the old finishes are being reborn.


From the original questioner:
What are the pros and cons of shellac? Aside from finishing the parts of a project before assembly, I still don't see how to keep the shellac from pooling in the corners. Contributor D did shed a little insight. They say it brings out more color and grain (depth). In the eye of the beholder? Color I can see because of the amber tones in shellac. To me all that does is make the piece look older by turning it yellow, and that has its place. That's something I can achieve with stain and poly. I really do like the fast dry times. I could actually finish a project in a day rather than over 5 days with poly.


From contributor S:
Is the article you speak of about French polishing? If so it takes a little time to work out the technique.


From contributor C:
Contributor E, being a student of historic coatings from Egyptian era to present, I'm interested in your comments on the use of linseed oil and shellac and spar varnish formulations. I have seen no mention of this in wood coatings in my readings, and from classical Greek or Roman periods, a few mentions of concoctions arise, like the writings of the monk Theophilus, describing an oil varnish molten "resin" into hot oil (though the oil or resin is not described).

In the Renaissance period, we have Cennini's mentions of a 15th century recipe which describes the running or melting of rosin and sandarac and mastic varnishes containing water purified linseed oil, that were applied by sponge to armor and the like. Jan Vav Eyke and Leonardo are thought to have used oleoresinous vehicles with amber varnish, along with other vegetable oils, but I have never come across what you state.

To the original questioner: Could you give me the formula you're using?



From the original questioner:
The article is in Woodsmith, Vol.32/No.87, page 46.

I first cover the project with bls, then multiple coats of shellac, finishing it up with one coat of thinned satin poly. I did miss that they are diluting a 3lb cut 1 to 1 with denatured alcohol.



From contributor C:
So the article tells you to apply boiled linseed oil on the wood first, then wipe any excess off, then apply your 1 1/2 lb cut shellac over the top with a lint free rag. This is an early form of friction polishing, more commonly called French polishing. The original French friction polish used in the times of Louis the XIV by the leading cabinetmakers and finishers did not even contain lac/shellac. There was no refined shellac at that time or bleached shellac. The polish of those days was mainly sandarac resin and in time other more elastic resins like mastic to make the polish less brittle. Also, spike lavender oil was used as a plasticizer.

The old milky waxy seed lac or orange or button shellacs looked terrible and were way too dark for the fine wood furnishings and light veneers at that time. They were relegated to use on cottage furniture at best.

Formulas for wood finishing with BLO and shellac were very prevalent in the 1800's, mostly in America. But these are outdated and inferior formulations.

Boiled linseed oil darkens as it ages - sometimes extremely - and can ruin the original look. Tung oil has been used also and though it avoids the darkening of BLO or LO, it is a drying oil, and oxidative properties separate from anything present in the shellac pits drying and hardening properties against each other.

The bulk of the oils mentioned will sweat to the surface and are normally wiped off with a barely moistened polishing rag quickly wiped lightly over the surface so that it is taken up without disturbing the high gloss of the polishing action at the end of the process, but there is still a minute amount of oil present in the film. If there long enough, it will polymerize within the shellac itself. It's a microscopic amount but its oxidation is still fully present.

This can be proven by applying this technique to glass or other substrate that's polish-able, and building up the oil and shellac as if on wood, to a fairly thick film, allowing it to dry totally for a few months and then scraping the coating off the chosen substrate, re-dissolving the entire film and placing it in a clear glass container (preferably a chemistry beaker or test tube). Let set till the components have separated out to their own different levels or speed it up if you have access to a centrifuge.

What you'll find is three levels - a fairly clear liquid on top comprised of mainly alcohol, a fairly large amount of more concentrated shellac that has settled, and a very small film beneath this of sedimentary oil. It's best to do this with the lightest shellac blond so it is more easily seen.

If you want to lay down a wet coat of tung or BLO on the wood and let it dry/oxidize and then apply shellac over it, that's fine, but you would be much better off using light mineral oil if you wish to pre-lubricate the wood surface and also use a few drops of it for the outer pad surface contacting the wood as a lubricant to help stop the pad from sticking to what polish may already be laid down, known as "spiriting off." This technique takes time to develop. Also the mineral oil will not be bound up in the finish and will continue over a long time to sweat out of the finish in microscopic amounts, and normal household polishing will remove it.

If you're really bent on learning this centuries old technique, buy a book or video, or find someone who already knows this and ask them to teach or show you. I think Jeff Jewett has one, as does George Frank. Check your local area for finishers that may show you in person. I may have just wasted my time if this is an article about padding shellac on wood surfaces, which is an offshoot of French polishing, calling for a wet pad of shellac to be used.



From the original questioner:
Thank you. Is Sam Maloof's finishing formula similar to this and is it a better finish?


From Paul Snyder, forum technical advisor:
I haven't seen the article you're referring to but I'm familiar with the linseed oil, shellac, varnish topcoat finish. It's been around for a long time and remains popular with some of the folks that prefer hand applied finishes. I have a sample on cherry that includes the linseed oil and shellac here:

Finishing Cherry

The linseed oil is used to highlight the directionality in the wood grain and bring out its shimmer/chatoyance. It works nicely on cherry, but doesn't have that much effect on other woods in the tests I've done. And you don't need to worry about the linseed oil getting too dark since it's going to be topcoated. Linseed oil exposed to the air can turn dark, even black, if exposed to a mild acid like vinegar (contained in some cleaners). The shellac is used to seal the oil and add its own color. Shellac is a good choice over linseed oil because it will adhere well even if the oil isn't fully cured. Finally, the oil-base varnish provides a lot of durability (e.g., wear, water and chemical resistance). If you plan to use oil-base poly, it's best to use dewaxed shellac to improve adhesion with the poly.

The solvent for shellac is alcohol and it does evaporate fast. It's going to be a lot different to work with than the oil-base poly you're accustomed to. On a small object with inside corners, you may find the best results by brushing or even using an aerosol spray can (Zinsser or Pre-Val).

During the French polish method you can use mineral oil or raw linseed oil as the lubricant. Mineral oil is used in the French method and linseed oil is used in the British and American methods. To quote from Sam Allen's book, "Only a tiny amount of oil is used and it is removed from the surface at the end of the polishing process. Some people believe that the oil mixes with the shellac, but this is not correct; the oil is simply a lubricant to aid in the application of the shellac."

There are slow evaporating solvents you can use in small amounts (e.g., 1-3%) with shellac to give you more work time. These include EB (Ethylene Glycol Monobutyl Ether), butonol, isobutanol, butyl cellosolve, dipropylene glycol monomethyl ether (DPM) or lacquer retarder. If you do a Google search for "evaporation rate" for each of the solvents you can make a comparison of how slowly they evaporate.



From contributor R:
I have had good results using the following method to obtain a finish which is not darkened as much as a rubbed oil finish, shows the grain pores, and is quite durable as an interior finish:

1. Prep the wood surface using 220 grit, wet with water and "whisker" the surface by rubbing 0000 steel wool against the grain. You may use a cabinet scraper after this technique if you have the skill and time.

2. Shoot shellac liquor (de-waxed shellac off the shelf mixed with 1 1/2 X denatured alcohol let settle for a day, decant the amber colored liquid leaving the yellow solids in the container), add lacquer retarder @ 50 /50 to the liquor.

3. Depending on the density of the wood, shoot two to three coats of this material (HVLP gun) on the wood to create a shiny surface but with pores showing, let harden overnight.

4. Steel wool 0000 again until all gloss is finished to a matte sheen, apply Duraseal penetrating oil with rag, let stand for 10 to 15 minutes and wipe off vigorously (important). Let stand two hours and reapply oil two more times, rubbing each coat as above.

Results are a fine sheen which has maintained the luster and refraction of the original substrate curl blister without killing this luster and is extremely durable indoors only.



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