oil under shellac, myth or magic?

M

msiemsen

Well-known member
We were discussing the use of oil under shellac on a previous thread,
http://www.sapfm.org/forum/index.php?topic=1180.0  "Shellac and Boiled Linseed Oil"
and I see it mentioned again,
http://www.sapfm.org/forum/index.php?topic=1267.0  "Finishing curly cherry"
I have seen no difference in my samples on the same board with or without oiling first. Does anyone have any side by side samples made on the same board that show that oiling improves the finish? My sample is getting fairly old and I still see no difference. I see this oil under shellac mentioned often and I have yet to hear from someone with a side by side comparison say that it makes a difference. If you have such a sample that shows such an improvement to make this step worth doing let us know about it.
 
Mike, I'm doing side by sides with: 1. just shellac, 2. just tung oil, 3. oil, then shellac, and 4. oil, then shellac, then poly, then wax.  Should be just a few more days and I'll post it on my blog.  So far, the oil under shellac is prettiest, in my opinion.
 
I think it makes a difference too. Especially bringing out the grain on curly maple. I use an aniline dye, BLO, then shellac. The oil really makes a difference in the curl. I'm not sure sure on other woods.
 
I made a small sample with curly maple a couple years ago, and saw no difference.  The grain "popped" just as was well (in my opinion) using only shellac.  Therefore I finished the piece with just orange shellac.

Tom
 
John,
I am trying to find out if this actually works for people. Try a sided by side comparison on the same board and see for sure.
Kari, I look forward to seeing your results. You are using Tung oil which is different than BLO which is what I was really looking for but I see I didn't specify. would you try a BLO sample too?
Mike
 
Hi Mike,
I haven't heard from you in awhile, i hope everything is going well. As far as the oil under shellac question, There is a definite difference, But not in appearance. The difference is in finish adhesion. by filling the pores of the wood with oil, the shellac will not penetrate as well. As far as difference in appearance, you can get the same affect by simply tinting your shellac. The greatest pitfall with using BLO, is that it starts a deterioration process that will turn your finish black. Yeah i know BLO has been used extensively in the past and our history books are filled with old recipes using bizarre stuff. I don't understand why you would use something proven to cause negative results in an aging process. BLO is not used in the restoration/conservation field because of these traits. Why would you use it on something you've spent a considerable amount of time building? The use of polly over shellac can be interesting too. If you use the wrong formulation of polly, it could peel up like a sheet of plastic after exposure to sunlight and time. In my opinion, If you do good work, don't use polly. A good finisher or antique dealer will be able to spot it from across the room and the first water mark you get will make you sorry you ever did it.

- Randy
 
Mike, sorry--I didn't specify. I did use BLO under shellac on the oil/shellac tests.  For the one with just oil, I used tung oil. 
 
Kari et al,

First we seem to have 2 threads with the same subject running simultaneously. I don't know how that happened, but in the other thread I provided some comments back to Mike about my observation of a test piece (BLO under shellac vs. shellac only) I did about a year ago. No point here in restating all that.

This just to say that I too am interested in your observations once you're done. The key question for me about your test is: How much time do you plan to give it?

My feeling is that initially, based on my unscientific test, the BLO treatment does make it look prettiest while still fresh, but after awhile there seems to be no difference. 

Though I still plan to use BLO for various and sundry reasons as a base under shellac in the future, Randy's comments about the blackening effect over time give me pause. Perhaps tung is a better, albeit slightly more costly, alternative to achieve some initial build.

Rick Yochim 

 
Hello all'

1st  I am new to this forum and have read many of the old posts. I am very impressed with the level of discussion, and very happy I have found it.

2nd  I am not questioning any ones posts or opinions and do not mean any disrespect to any one. I only ask these questions because I want to learn.

I have read on this forum and a few other places that using BLO will cause an item to turn black over time.
            1.  how long does this take?
            2.  does this always happen?
            3.  is it caused by the BLO alone, or is there some other factor involved, atmosphere, mildew,
                mold, something mixed with the oil, or some other factor.
            4.  where is the research that supports this claim
            5.  is all the linseed oil on all the furniture and in all the oil paintings in all the museums in the
                world somehow being removed or mitigated
            6.  isn't linseed oil in most old varnish
            7.  is there a differance between BLO and plain linseed oil in this effect
            8.  is there a differance between old BLO with lead and modern BLO with out lead
            9.  does this effect contribute to what we call patina

Again I am not trying to be a smart ass I really just want to know.

thanks in advance Tom 
 
Hi Tom
I was always told a bad question is one that doesn't get asked. There are many documented cases of BLO turning black over time (i believe you can check the AIC archives for cases). Besides turning black, BLO is also a good food for mold, has poor UV qualities, has a very poor drying qualities and once polymerized in the wood is difficult to remove. now if that isn't enough to put it back on the shelf, the chemicals added to make the stuff are known cancer causers.
-How long does it take to turn black? this is a difficult question to answer because of enviormental factors (moisture, UV, temperature, etc.) but in the research I've found black finishes were results of BLO (most of the time). Furniture polished with BLO over the years creates a gummy or what i call a grungy surface and is difficult to remove and not pleasing to the eye. The paintings I've seen coated with BLO are usually sent to a conservator for repair due to the darkening of the film. As far as museum furniture goes, that's always been a difficult question to answer due to different opinions of the museum curators, some call this an original finish, some call it damage. BLO was used extensively in the past as a preservative or binder in paints. Keep in mind BLO of the past is not the same formulation as what is made today. Plain linseed oil does not contain chemicals to enhance the drying time. Plan linseed oil may take a week or two to dry or more depending on enviormental conditions. BLO has chemicals added to enhance the drying time. The BLO of the past contained lead as a UV blocker as well as to enhance it's durability, of course you know lead is not used in finishes today. As far as contributing to the patina of the wood, in my opinion, the negative effects (darkening) are not considered patina, but more damage. Once the BLO turns black there's not much wood left to see.
You might be sensing that I'm not a fan of BLO and it's uses. Besides being inexpensive the only other use i find would be in glazing putty. The negative effect of aging outweigh it's benefits as a wood finish. For any place you think you could use BLO in todays' chemical world, there is a better product out there. One of my old instructors once told me the only place for BLO would be on fence posts because it was cheap, and of course there are better chemicals for that too.
I'm encouraged by Kari's experimenting with finishes, i did these same tests 30 years ago when i was in finishing school. It is difficult to know when the BLO is dry enough to add finishes to the top. Adhesion tests can be done by scoring the top in a checkerboard manner an applying tape to the finish to see if you can lift it off.
Keep experimenting (I've been doing it for 30 years), keep asking questions and don't stop learning. This is a field that changes as much as the weather.

-Randy
 
You will usually find two schools of thought regarding shellac over oil much like the one about whether it is correct to place your hand plane on the work bench down on its side or on it's sole.

If we look at what oil finishes do independently of other finishes, we usually say that they are meant to enhance the beauty of the wood's grain and color. If we look at shellac independently, we see that it too enhances the wood's grain and color but also adds more sheen and more protection than true oil finishes.

Since shellac is an evaporative finish, meaning that each coat "melts" into the previous coat, we do not build up multiple layers with shellac like a reactive finish would behave. (i.e.  such as varnish or other heat-bodied oils that are sometimes referred to as polymerized oils, etc.). In other words, we are building one single layer of shellac with multiple coats. If we looked and compared the applications of equal coats of shellac and then varnish, we would see one big, single layer of shellac and with the varnish, we would see and count distinct layers separating each coat not unlike a tree's growth rings. Lacquer is also an evaporative finish and provides the same single layering effect as shellac.

If we understand how the incident and reflected light on the wood surface behaves, we see that "single" layer effect of shellac and lacquer offer less resistance to light as it transmits through the film and reflected off the wood surface back through the "single" layer before our eyes react to what they see. In the case of varnish and other reactive film finishes, light is interupted at the boundaries of each layer which causes added attenuation of the incident and reflected light before it reaches our eyes. In addition, there is a color or wavelength shift occuring much like a prism behaves when we transmit sun light through the object. We call this refraction. Thus, we have increased distortion of color and other wood grain details due to more attenuation and refraction unlike the more jewel-like appearance of shellac and lacquer.

In my opinion and observations from my years of using shellac, oil and by doing a comparison in sun light of multiple coats of shellac over an oiled surface vs. just plain oil, I think you would see the difference however subtle it may be. Based on the above, shellac over oil, be it BLO or Tung oil, should accentuate the oil's effect on the grain and color more so than just plain shellac or oil.

In regards to the wood darkening over time from the use of BLO or even Tung oil for that matter, does pose an issue that one needs to weigh out carefully. However, just remember that the effect takes many years and not likely to pose a serious problem in one's lifetime.

Mickey



 
Hi all, I posted the finishing experiment here: http://villagecarpenter.blogspot.com/2010/01/finish-line.html

Hope it helps. The photos aren't great, because not only am I not a finishing expert, I'm not a professional photographer. ; )
 
But we will make a finisher of Kari, given time, advice and experience. Or perhaps by dragging her kicking and screaming into the world of finishing...

Gary
 
Kari, your post on The Village Carpenter is most interesting!  It is very hard to take pictures of finishes.  On  another note, what is  object # 22 in your slideshow?  All your work looks to be of very high quality.

Jim Vojcek
 
At the Village Carpenters site, just below your picture, is a slide show.  Click on any picture and you get a full screen of it.  To the left are picture numbers 1-30.  Take a look at #22, right after the mallet and before the Celtic cross.

jim vojcek
 
That's funny--you know more about how to work my site than I do! haha
That is a chisel rack that sits on a shallow shelf in the door of my tool cabinet. The "feet" aren't attached. I just use them to keep the rack steady when it sits on my benchtop. It's made from cherry. There's foam glued into the compartments in front of each chisel so they don't tip forward or sideways. The chisel booties are made from leather--my first sewing job.
 
Having read most of the posts I would like to emphasize a few points.  Shellac over an oil is not advised chemically speaking because of potential adhesion issues due to varying surface tensions and cure rates.  Oils and poly-resins are the two types of finishes one does not want to use shellac over.  Doing so is just revisiting the days of period experimentation long before proven advances in organic chemistry.  Shellac is the miracle resin of the ages.

Shellac in it's many forms and formulations needs no help, with exception to mineral oil in French Polishing.  Proper formulation and application are key.  Beginning with the right flake for the correct purpose. Differing flake can be blended for specific results and purposes.  This is another topic, however, the correct cut is paramount.  Having studied most of the literature on the topic going back 200 years it always begins with a one to two pound cut.  I prefer a 1 1/2 pound cut put into solution using pure ethanol.  Application is always best with a narrow 1 to1 1/2 inch rounded tapered watercolor brush.
Irregardless of the square footage.  Watercolor brushes such as a Windsor Newton Golden Taklons last longer.  Beaver mops or goat calligraphy brushes work beautifully well but do not have the life span.  Least is best, working within small windows or areas, deftly overlapping and paying proper attention to consistency.  Many seem to miss this point slipping into outer space during application.  Once, practiced proficiency is acquired one can brush a top in the same amount of time it can be sprayed only with 100% transfer efficiency.

Adding dyes such as Transtints, Mixols, and organics such as Dragon's Blood will increase depth and provide proper color for most period work.  That being said, BLO was the practical finish of choice for the majority of Furniture Americana until 1820.
 
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