Chatoyance

      Some woods (with some finishes) offer different looks when struck by light at different angles. Call it shimmer, moire, chatoyance, or whatever — this thread tells you all about where it comes from and how to enhance it. September 26, 2006

Question
What is the most effective way to bring out the shimmer in woods such as cherry? I use lacquer and get good results. However I wonder if linseed oil or shellac before lacquer would yield superior results? Sometimes when reading on this subject they recommend one product for highlighting the color and one for bringing out chatoyance. What is the difference? Are they referring to the amber nature of most shellac?

Forum Responses
(Finishing Forum)
From contributor A:
In my opinion, usually that word is used in the same way as popping the grain. It brings out the markings and features in the wood. Usually, boiled linseed oil is mentioned, but any shellac which contains color will also do it. In fact, any colorant will do it, be it a dye or a pigments stain. You need very little color in the solvent to bring out the chatoyance or to pop the grain in the wood.



From contributor B:
The best way to explain chatoyance is if you have ever seen a conference table or just a table with a diamond match or starburst match veneer, the color on a couple of the leaves will be darker than the rest but as you move around the table the color will change in relation to your position. On a muddy finish this will not happen. Also on rail and stile doors the rails will look darker from one viewpoint and the stiles will look darker from another viewpoint and straight on they will be the same color. So chatoyancy is finishing wood so that it retains that ability to change color at different angles. This usually requires using dye stains or chemical stains. Do some samples, take them out in the sun and check them out.


From contributor A:
That's why I mentioned about it takes very little color, even when you’re using dyes. The lighting in the room also plays a big part in the appearance of the wood at different angles and seeing the changes in the wood..


From contributor C:
Light bounces of the fibers of the wood. Dye has a better effect because it is more translucent no matter how light or dark you go.


From contributor D:
Sanding the wood to a higher grit will also contribute to chatoyance. I've turned maple, walnut, and cherry items on the lathe and sanded them to 6,000 grit using micro-mesh abrasives "12,000". With no finish whatsoever, the wood looks like a hologram. However, don't sand a product like that and expect lacquer to stick to it, I strictly use linseed oil or danish oil on such things.

Sand the wood up to 220, but not beyond that. If you are using a high-solids precat or conversion varnish, stick to 180. Be sure to always hand-sand with the grain just prior to finishing. Spray your first couple of sanding coats thinned. I've noticed that two or three thinned 50/50 coats will produce more shimmer than one normal sealer coat. The flatter the final finish, the more iridescence you'll see.

Also, glossier topcoats will show off the shimmer better, and defects too. You can't have it all, unfortunately. Beware of using any oil under lacquer. It can be done, but must cure for a week. Also I doubt any finish manufacturer will honor its guarantee on any finish with oil under its product. I've done it for personal items and it looks good. But I wouldn't do it for sale.



From contributor E:
To contributor D: When you warn about using oil under lacquer, would you please explain what you mean? Also your statement that it must dry at least a week needs some clarification as well.


From contributor D:
The original questioner asked about using linseed oil under lacquer to pop the grain or bring out the shimmer in wood. This can be done, but linseed oil and lacquer don't adhere to each other at all. But since linseed oil is a reactive finish (catalyzed by atmospheric oxygen) it will harden enough in the week's time so you can topcoat with lacquer.
I forgot to mention that I strongly recommend using vinyl sealer under anything you spray when using linseed oil. Vinyl sealer will seal in any contaminants from the oil. I use vinyl sealer occasionally when refinishing my own furniture, and topcoat with two or three conversion varnish coats.

I hope this clears things up. I wish I had a picture of the mahogany bowl I made a month or two ago that I finished with linseed oil and then sprayed with precat a week later. Man, what a nice looking combination. It violates every rule ML Campbell stipulates for using their product but it works for me. Again, I'd never use an oil under lacquer products for a production item. There is too much risk and too much time waiting for the linseed oil to cure. That, and linseed oil is horridly flammable - just a rag dampened with it totally char-broiled and gutted another local cabinet and millwork place. I only apply it with paper towels which get a good water soak and get sent down the garbage disposal.



From contributor B:
Sherwin Williams makes a clear stain base concentrate in their S64 series that can be used, similar to a natural watco oil, and is compatible with lacquer. I use this with highly figured woods like anigre or tiger maple to bring out the figure without the risks involved with linseed oil products.


From contributor F:
Chatoyance ("C") is the result of light reflected from wood cells that are not all nicely aligned. Rather, sometime during the growth cycle cell groups took on different wavy directions. When viewed from one direction, some cell groups will reflect more than others but as the piece is moved, a reversal occurs. You are seeing the cell groups from a different aspect and their colors have changed. If you've ever had to try to repair a piece like this, you know that it is impossible to do with the usual arsenal of powders and sticks.

"C" can be enhanced by enhancing the color differences between the cell surfaces and this can best be done with dyes (water soluble is better here) or colored, transparent finishes. That's why amber shellac, oil, and NC Lacquer work well - they have color and they are transparent. If you want more enhancement, use multiple coats of very dilute dye or multiple coats of very thin shellac (1/2# to 1# cut) to which an alcohol soluble dye has been added. Stay on the lighter side and build your color with multiple coats. Sand lightly with very fine paper between coats. When you get the look you want, finish it with a transparent coating. Different woods have different cell sizes and grain structures and will react differently and some woods need more color added than others but this approach will work for most everything. The dye and sanding enhances the color differences and the transparent finish enhances the shimmer. I have a piece of cottonwood burl that barely shows "C" in its raw state, but give it a couple coats of orange dyed shellac and it looks like it's on fire.

I have also seen (but not tried) chemical stains that really pop the grain on some woods. A gentleman name George Frank who wrote a lot for Fine Woodworking produced some spectacular results using ferrous sulfate on figured maple. Forget pigments - they will only hide, bury, obscure, muddy, or mute what you want to enhance.



From contributor A:
To contributor F: I take exception to your comment on pigments. It’s not the pigments that paint the wood, it the finisher. People like you give pigments a bad name because you probably never spent the time to learn how to use these colorants. I stand by my original comments, that any color will add the chatoyance to the wood. Look at some materials that are now mentioned by some of the others, such as danish oil and clear stain base. Even you mention "That's why amber shellac, oil, and NC Lacquer work well - they have color and they are transparent".

If you look at my post, you will see that is exactly what I said, “Usually, boiled linseed oil is mentioned, but any shellac which contains color will also do it. In fact, any colorant will do it, be it a dye or a pigment stain. You need very little color in the solvent to bring out the chatoyance or to pop the grain in the wood."

It’s the contrast of that small amount in of color that actually is all you need to get that effect. When different woods are used, any coating with an amber cast will bring out the chatoyance. You don't need chemicals to dye the woods - all you need is a little color.



From contributor G:
I have done many finishes according to what contributor A says here, and I can tell you in fact that what he writes is not just bookish but it does actually work. He is dead on that it is a finisher that ruins or makes a dancing finish, not the materials. Do dyes in general do a better job with grain popping? In general, yes, but depending on techniques and materials, not always. My grain popping is sometimes done using pigmented materials.

Painting out a finish is the opposite of getting the grain to pop. That does not mean that all pigmented coloring steps paint out a finish. This is pure hyperbole. Painted out finishes are done by finishers using pigmented materials in such a way that they end up with muddy and painted out finishes. Now we are talking technique more than we are talking materials.

Now back to contributor B’s use of clear stain base. I think that this use of material is also called an oil sealer, and that's what it's used for - to bring out depth, a/k/a chatoyancy, a/k/a vibrancy, in the wood's look. The deeper any oil will penetrate, the more depth and vibrancy you will get. That's why linseed oil works so well because it stays wet and keeps working itself (wicking) deeper into the wood before it starts to set up. Shellac adds the aesthetic effect. There is something unusually clear and depth-producing about the shellac molecules. Shellac has so many great benefits and this is just one of the miraculous ones. Grain popping is not just science and technique. It is also an art. And there are many routes to take to get a successful look - none of them are wrong and none of them are the one right way. All roads leading to Thebes will get you there.



From contributor D:
It's pronounced "shimmer" to your customers. If I told some of my customers that the wood had a lot of chatoyance, they'd tell me they didn't ask me to use chatoyance on their cabinets.


From contributor A:
I think that it was Michael Dresdner who was the one that promoted that word. He was the first finisher who I ever heard to use the word chatoyance referring to finishing.


From contributor H:
Chatoyance is a term that is often used in reference to minerals and gems. Iridescence is another good synonym.


From contributor I:
These are great comments from a lot of knowledgeable people. I love the way boiled linseed oil hardens the grain and conditions the wood to a definite depth - sometimes a lot more than you think, especially open pored woods. I feel this gives the clearest view into the board and seems like a lens to enhance the figure iridescence or glow or chatoyance. Color does add noticeable contrast. Commercially we have to use a lot of pigment stains to even things out for the mass appeal. I try to relate stains to two groups - dyed oils, such as MW golden Oak, Provincial - and Pigmented spirits based like MW 225 red mahogany and colonial maple. We make lots of test samples.


From contributor G:
I might not have the gravitas of Michael Dresdner, but the word "moire" is much more a propos. Ever see "the wave" done at a football game? Ever watch large groups of soldiers march in lock step? This is more like what vibrant wood does. The grain of the wood seems to follow you around the room like the eyes of the Mona Lisa painting. More simply explained to customers, it's the "nap" of the wood grain, just like velvet. And to me, that's why "moire" is a more fitting word for this visual wonderment. Be prepared on quarter sawn oak to have some customers complaining that there are areas where your stain did not take (namely the flecks and medullary rays).


From contributor D:
What woods commonly used in cabinetry tend to produce the most spectacular? I've noticed walnut tends to be like a hologram when done properly.


From the original questioner:
Thanks guys for the ideas. I have done much testing and now I see why the diversity of opinions - I often got differing results on different boards of cherry. However, I have concluded that oil does not seem to affect chatoyancy, neither does the clear stain base. The oil may deepen the color a bit, though. Once topcoated with lacquer, the shimmer was identical. Walnut seemed to be the same way.


From contributor A:
All it takes is a little color. If you take two panels, and use an amber color coating on one panel, and a water clear on the other, and spray a few coats on each panel, you will see the amber coating will look better. On certain woods it takes more contrast to change the colors.


From contributor J:
Water dyes, especially if layered on in separate colors rather than mixed, will create visual depth, are very lightfast and will not turn dark over time like linseed oil. If you add some diacetone alcohol to the dye they will penetrate even deeper. Potassium dichromate will chemically impart a beautiful soft and natural patina on cherry. Shellac is a low molecular weight material which is why it saturates so deeply and brings out the natural chatoyancy.


From contributor A:
Speaking of chatoyance, I recently did an article in Custom Woodworking Business. I think you might find the beginning of this article interesting, and see the tie-in to this thread on chatoyance. Related link: Article


From the original questioner:
To contributor A: Yes, I have also found amber dye in lacquer does help chatoyance. I have not experimented yet a whole lot with dyeing the wood. Do you think it is a better affect that simply dyeing the topcoats? Shellac is not an option as a topcoat as I do lots of dining tables. Would a shellac sealcote before lacquer make a significant difference? The amber color is a non issue since dyeing the lacquer is easy enough.


From contributor J:
I think you will see an extraordinary difference. The chatoyancy is not a surface effect - it lies deep in the wood fibers. The deeper the mordants or dyes penetrate; the more layers of visual depth are brought out. Again, it is the transparent coat that then brings out the color and beauty of the dyed fibers. Because of its' LMW, shellac will saturate deeper than surface coats therefore popping the effect at a deeper level. Drying oils turn dark over time, and the next generation will not see the beauty of the piece as you have created it today. I make my own shellac using Button Lac and filter out all the wax to make a fine amber French polish. I also add a UV stabilizer. One coat of this, then finishing with what you like for top coat, should make the wood dance as you walk around it. Warning - might even make you dizzy. Have fun!

Experiment (on scrap) with water dyes (I like Lockwoods) in terms of layering them. If you want to get a golden orange, lay down a yellow first, let it dry, then lay down a red, with maybe a walnut crystals over that. Then mix them all together equal ratios and apply them and see how different a look you get. By layering you can create visual depth and even faux graining effects with different colors accenting the cathedrals and such.



From the original questioner:
Tell me more about the UV stabilizer. Where do I get it and can it be added to lacquer?


From contributor J:
The UV stabilizer I use is called Tinuvin 292. It is a hindered amine light stabilizer (HALS). It helps to prevent ultraviolet light from breaking down the film itself. It can be used in low molecular weight resins only, so "no go" with the NC lacquer. Manufactured by Ciba-Geigy, and you can buy it from the Conservators Emporium division of Museum Services Corp. I add 3% to weight of resin content for my french polish. Let me know if you are interested in the recipe I make.


From contributor F:
What is the purpose of HALS in the shellac? I learned someplace that shellac is naturally more resistant to photo degradation than most any other un-pigmented finish. Is that not true?


From contributor J:
I am not a chemist but I'll give you the long and short answer. Yes and no. Yes, shellac is certainly a more stable resin compared to many others. Yet, still is affected by light, most especially sunlight, and oxidation. It does degrade, craze and crosslink. The word "finish" encompasses a huge range of materials both of natural and synthetic origin. There is only one "finish" material which I can think of which is not chemically altered by light, and that is beeswax. Nitrated cellulose self destructs even in the dark but light will drastically accelerate the process. Tree resins, plant waxes, bitumens and oils are all affected. (I am unsure about the fossil resins, but it is possible since their suspected origin is tree resins.)I put a HALS in my shellac because I can and I desire to provide the protection I can. I could, but do not, add a UV light absorber. That is a whole other subject.


From contributor A:
To contributor J: You must be a conservator? Can you tell us what would the extra time in years that one would get from using these " blocking and screening" products on furniture that was left in direct sunlight? There is a lot of hype about inhibitors and blockers. I'm sure you know that simple colored pigments and silica flattening agents have shown they also are good for sun blocking. I don't see any of the major furniture or kitchen cabinet manufacturers promoting these sun screeners in their finishing. I don't think these products have proven themselves in finishing or in restorations. If they had, they would be promoting these products to all of the other allied industries.


From contributor F:
To contributor J: Fair enough. Shellac certainly does degrade over time and sitting it the sunlight does accelerate the process. I'm not a chemist either but I do know that HALS is a free radical scavenger. It interrupts a photochemically initiated chain reaction in polymers that leads to coating failure. It is different than a UV absorber or a lignin stabilizer. I didn't know shellac was classified as a polymer?


From contributor J:
To contributor F: You're right that the early antioxidants, such as BHT, act as radical scavengers, hence chain stoppers. Being oxidized themselves in the process, they are eventually used up and cease to play their role. They work best as stabilizers against thermal auto-oxidative reactions. They perform poorly in the presence of light. HALS is a new class of antioxidants which are effective against photochemical degradation. The action is complicated but the antioxidant is not used up which makes them the most effective light stabilizers currently available. I’m not sure if this was a question or if this answers it, but shellac consists largely of low molecular weight polymers (oligomers).

Kitchen and furniture manufacturers don't bother to hype their coatings anymore. It is assumed they are all up to snuff. Many coatings manufacturers are putting UV absorbers in these days. This is for color retention not film stability. Kitchen cabinets are not intended to be handed down from generation to generation unlike the dining tables the original questioner is doing.



From contributor A:
To contributor J: I think you need to look further then the conservators hype, as all the UV absorbers and blockers being used today are still being measured in years. The furniture and cabinet companies that use them are basically the companies that are curing their pieces with UV, and not the majority of manufacturers that do their finishing in spray booths.


From contributor F:
To contributor J: Thanks. I'm not sure I would classify HALS or Tinuvin as "new". There was a fair amount of research done in the late '80s and early '90s on the various natural and synthetic coatings used to protect museum paintings. Tinuvin in dammar and mastic were two of the natural resins evaluated and were the basis for evaluating the various synthetics available at the time. The reason they added HALS was not to protect the film from UV degradation (museums are UV free) but to preserve the film's solubility. The unstabilized films would oxidize and cross link I guess (even absent UV) becoming insoluble - not good. Now I've said nearly all I know about Tinuvin. So when I saw your recommendation to add it to shellac, I was curious to know what the benefits were since I've never had a problem with shellac becoming insoluble, (less soluble – yes; insoluble - no). It's already very light stable. I got your answer but I still don't see what the technical merit is.

There are plenty of alternatives but this is what I do to enhance chatoyance; Sand very fine (220/320), cut some Zinsser Seal Coat 50/50 (tinted if you wish) and soak it into the wood, sand again (320/400), follow with 1 coat of uncut Seal Coat, Top coat. Damage to or failure of your top coat will most likely cause you to refinish long before your shellac causes a problem. There are many, many different shellacs. Some are great and some aren't worth anything. You'll get good consistent results from fresh Zinsser but if you want to mix your own try Gold Dust from Touchup Depot - dissolves in minutes.



From contributor J:
To contributor F: You’re right. I tend to over simplify often. "New" is a relative term. Although I would guess that there are more small House Museums in the world (than Getty's and Guggenheim's) with no money for UV free lighting or UV film filters and sunlight streaming in on the artifacts, and HALS is a protective measure which affects film stability mostly in the absence of UV wave length.

Dammar and mastic tested in a fadeometer with UV filters have been estimated to have a useful life in excess of 100 years. So it has proven to be a useful stabilizer even in the absence of UV. When I filter all the wax out of my shellac polish I am removing the natural plasticizer. I remove it because it makes the polish cloudy. Without it, shellac becomes a very brittle resin over time. I replace the wax with some Manila copol (as plasticizer's) and benzoin (smells nice) and also add some Acryloid B-72 (a very stable Ethyl Methacrylate copolymer ). The HALS that I add has much to do with the addition of the copal and benzoin. It is a personal choice which I mentioned as a side note. I dissolve it all in 190 proof ethanol, instead of denatured.

Aldehyde groups are easily oxidized and in shellac are gradually converted to carboxylic acid groups. Further esterification resulting in cross-linking can continue in a shellac film. Shellac does become less alcohol soluble with time. Still, you are right – the original questioner is not going to have any trouble with a shellac undercoating, not in our lifetime. The one thing I do know for certain when it comes to chemistry and molecules is "shift happens!" To contributor A: UV cured coatings are cured by UV. An absorber/blocker would prevent the cure. They add photoinitiators, not inhibitors.



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