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Eight years later


Janel

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:lol: I just completed a conversation with a client who purchased a carving several years ago. This lovely piece had been colored with artist's oil paints, the leaves a delicate light spring green and the root part a variety of browns and warm tans. The owners report that the color is now all browns, very different than its original color.

 

What dismaying news. I had anticipated that the artist's oil pigments would have been stable. I guess not. I doubt that we will launch into a repair of the color, but we do want to have a greater understanding of the change.

 

Help me consider the various reason for this occurrence.

 

The oil paint medium was likely a linseed oil. I will check the sources later. Is this going to happen to all the other pieces colored in this fashion? I surely hope not.

 

Thanks,

 

Janel

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Janel-

What were the colors and/or pigments chosen for the oil paint? Different pigments have different lightfastness ratings... Also, was the sculpture on display in sunlight? I have a better understanding of the ageing of watercolor paints- oils are generally considered more lightfast because of the oil vehicle- but the nature of the pigment may help coming up with a theory of what went wrong.

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Janel

Were the colors thinned to produce a wash? Reducing the body of the paint reduces the color fastness and the linseed oil in a thinned paint reacts with the wood producing a browning effect. Other thinning agents can also cause reactions. There is also the possibility that if the wood was an exotic that the chemicals in the wood reacted with the finish. I know that mahogany and cypress are two woods that can have finish reactions on occasion due to the natural oil in the wood. More information as Doug said would help in solving the riddle.

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Aloha Janel,

 

Doug got right on it with respect to sunlight = UV exposure. Another possible culprit is oxidation. Woods like purpleheart and Andaman padauk (vermillion) turn brown over time because of that. Old European marquetry inlays also. Do you treat the pigment like a wipe on - wipe off stain, or thin with solvents? The particles could be extended past their binders and actually leaving the surface. Long shot.

Another thought is the wood's Ph. Type of wood?

 

KC

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Thanks for the questions and suggestions. Generations - the web page

 

313_4.jpg

 

The color of most loss is what was used on the leaves of the iris. Grumbacher Artists' Oil color, Thalo Yellow Green

Semi-opaque

Vehicle: Alkali Refined Linseed Oil

Pigment: Chlorinated Copper Phthalocyanine, Arylide Yellow 10G, Zinc Oxide (PG7)(PY3)(PW4)

Lightfastness: II - Very Good

 

I may have used a different paint medium to thin the oil, or perhaps mineral spirits. I have done that with other pieces. I don't remember exactly what process was used with this one.

 

The wood is boxwood. It was on display in at least one exhibition, plus the show or more which I attended before it was purchased. I have not seen the piece since the color change. The description is that it is all brown, without any green present. the root part may also have changed.

 

The linseed oil in the paint may have eventually become more brown, the "wash" of color, which was transparent to begin with, may have eventually faded. I have asked for a photo to be emailed to me so I could see what it looks like now. Such dismay. It is/was such a lovely piece.

 

With this option for coloration out of my reach now, if it is going to change in ten years or less, what future do I have with such a technique? I have so enjoyed the use of oils to gently enhance my carvings. I don't know what to think about future work that would have had my own characteristic color choices. ;) Change is part of growing, and this departure from oil color is imminent. Sigh.

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Hi Janel

 

The problem looks to be compounded by yellowing/darkening of the linseed oil, which would mask some of the color. Since your colors are put on fairly thin, using oil as a thinner, there is a lot of oil that is visible on top of the paint (linseed can become quite brown) Perhaps using mineral spirits as a thinner, instead of linseed, would help. That way there is no excess oil on the surface, on top of the pigment.

 

I use artist's oils on all of my heraldic sculpture, and have never had a problem. However, I always caution the client to keep it out of the sun. I also have a much more intense color saturation, and use mineral spirits to thin to a wash.

 

Phil

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Hi Phil,

 

I took care of that extra post. Thanks for your encouragements. Would display lighting, like the steady lighting at a museum exhibition have some effect over time, similar to sun exposure?

 

The paint was described as semi transparent, and uses linseed oil as the vehicle and that I may have used more linseed oil for thinning, so the potential for a color change or loss in combination with using a light wood, and the unpredictable lighting in its life sounds like a reasonable "conspiracy" for the changes in this piece.

 

In a wood carver's magazine, I read about folks using a base or what might be considered a primer, before coloring the wood with acrylic paints. That would obliterate the natural grain in the wood, or mask the character of the wood, but maybe that wood does not have any character that would enhance the piece.

 

I wonder if there is a clear, non darkening sort of application that would hinder the darkening of boxwood before the application of the oil colors? Sometimes the grain contributes to the piece, sometimes it interacts with the coloration favorably. Mostly the first application of the paint absorbs the oil vehicle from the paint itself, and after that the coloration is on the surface, not an absorbed stain. Boxwood does not absorb stain very well or very evenly, at least the boxwood varieties that I have is that way.

 

Janel

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Maybe you could try soaking the carving in linseed oil first (or applying multiple coats), allowing it to thoroughly dry, then add the oil coloring. That way the paint vehicle won't soak in before drying.

 

Also, if the vehicle soaked out of the paint before drying, leaving mostly pigment behind without a "fixative," could the pigment simply have wiped off during handling? I can't picture folks keeping their hands off your carvings...

 

This fear is why I've always used a water-based coloring dye/stain before applying the final finish, avoiding acrylic or oil colors which really only leave the color on the surface of dense grained woods. The color of the dyes may eventually become fugitive, but unless the wood is worn away, it won't leave the piece.

 

It sounds like you could just have your client send you the piece, and re-apply the green coloring. The wood should definitely be sealed by now... It may also be prudent (in the future) to take a scrap of the same wood(s) with each carving, apply a sample of the coloring(s) and finishes, annotate and date them, and keep them in a dark place just to judge what happens in a more controlled environment. Just for posterity and your/our eventual edification!? ;)

 

Interesting conundrum, anyway...

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Hi Janel,

 

Tom has some excellent points too, especially with the handling problem.

 

Yes, museum lighting can fade colors very badly, depending on the type. It is a frequet problem, and museums tend to rotate their light-sensitive artifacts in and out of exhibits. The worst type of ligthting is fluorescant, which puts out a considerably amount of UV light. Usually museums will use UV filters over the lights, and sometimes a UV filtered plexiglass barrier as well. Artist's oils, as Doug mentioned, are considered relatively stable, and are usually exhibited at light level of around 150 - 300 lux.; watercolors and textiles are ideally exhibited at around 50 lux, which is very dim, and seldom achieved. Still, oils can fade. There was a famous English painter of the 18th century named Joshua Reynolds, who became as well known for his high-quality paintings, as for the fading of the red pigment that he used. (Scarlet Lake) During his lifetime, most of the paintings that he had done had faded to the point that red coats and flesh tones were grey.

 

Re sealers or primers, I always use them, but I don't want to see the wood at all. This was a commonly used practice for painted (polychrome) sculpture since the Egyptians. Most polychrome sculpture was sealed with a liberal coat of rabbit skin glue, followed by a layer of gesso. This was then scraped or sanded, and the surface was considered ready for painting. Gilded areas underwent further preparation. Outdoof work was given a coat of lead-white instead of gesso. I usually seal the surface with a coat of varnish, followed by a layer of grey, white, red, or yellow spray primer.

 

However, as I mentioned, a lot of my stuff is virtually a three-dimensional painting. A simple and commonly used sealer would be shellac.

 

Sound's like preparing a series of practice samples would be on order.

 

Phil

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Janel

I did a little research and asked others of their experience.

 

Most all have a problem with the wood darkening. I know that just about any light and exposure to any sunlight colors the wood and it is amazing how fast this takes place. The degree of light influences the speed of the change but it is inevitable.

 

I know of one artist that uses oils mixed in varnish to produce washes that do not hide the wood. Problem is that there is a gloss which could probably be taken down with pumice or a product called Wolwax used with lacquers.

Dyes can be used as there are some really light fast dyes made but I am not sure about creating custom colors or how you would anticipate the wood change to keep a color. From what I have been told and have seen the colors can be to vibrant at times. Experiments could prove helpful.

Latex paint thinned with water works well for coloring and holds up well to sunlight. This is something I have used for outdoor work. Care has to be taken or the grain can be covered up. I usually use multiple coats to build color for better control. It does not have the clarity of oils though.

 

Not all is lost in the coloring realm. I know that some of the alcohol stains are rather good and switching from the linseed to a cleaner thinner would work better. Lacquers with japan colors are a possibility and there is a flattening compound that can be added to the lacquer to control the sheen. Linseed oil darkens and I feel there has to be a better product out there.

Mark

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Janel,

 

I'm in agreement with much of what has been said. I double checked on the lightfastness of the pigments you mention and they're all towards the sturdy end of lightfastness. Modern green paints- often called convenience greens- are cocktails of pigments rather than one single color. Sometimes one of the constituents will fade out, causing a significant change. That doesn't seem to be the case here. However, you're applying such a light tint that I think it may be reasonable to drop them down slightly in their lightfastness- but to me it still doesn't seem much cause for worrying. I also don't think that the oil is soaking into the wood to an extent that the pigment particles are left unbound. It's good advice to thin your oils with turpentine or spirits rather than linseed oil.

 

Rather, I think the problems are twofold- the linseed oil is darkening- as Phil also surmises- and the wood is oxidizing to a darker color. The wood is going to oxidize by exposure to light (photo-oxidation). There are UV-absorbers available which I think (tenatively) can be mixed in with the oil paint. You may have to apply them as a varnish afterwards though. It would be best to phone up an art museum in Minneapolis and speak with their painting conservator- he/she will be able to recommend an additive to the paints and methods you're already using.

 

 

Good luck!

 

-Doug

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just spoke with the paintings conservator we have on staff here at IU. She said that a product line called Tinuvin (made by Ciba) is typically used to inhibit photo oxidation of oil-based paints. It would have to be applied in a varnish formulation, after the piece is painted. There are many, many varnishes out there you could use, and they can be custom tailored to suit your needs. Tinuvin is used in a lot of exterior wood varnishes for decks and siding, so it may be in a commercial UV scavenging varnish for the woodcraft market.

To reiterate though, I'd get in touch with a painting conservator locally and see about a formulation to meet your needs.

I'll add the caveat that auto-oxidation of the wood will still happen, causing gradual darkening.

 

-Doug

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Hi Doug,

 

Thank you for the above information, and much gratitude to you for taking time to speak with the conservators out your way. I will try to communicate with a conservator at the Minneapolis Institute of Arts. I wonder if there is a spray form of a product that would contain Tinuvin.

 

Janel

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