Michael Dresdner » UV protection

No fade, no shade

Michael — Tue, 15 Jun 2010 14:00:10 +0000

Q: We are in the process of making a dining room table out of solid padauk and purpleheart, and wanted to know the best way to finish it. We would love to be able to keep the colors of the natural wood, without ambering over time. A clear, durable finish would be great as well.
A: For a clear durable finish that will not amber over time use a waterbased polyurethane. It goes on clear and will not amber. For more durability, use a cross linking waterbased floor finish. However, neither of those will prevent the sun fading the wood. For that you’d want an exterior waterbased finish that contains UV absorbers and blockers, but it will be softer and not as durable. Even at that, it will only delay the fading of the wood colors, not stop it entirely. Sadly, finishing, like life, is full of tough choices.

Osage, oh fade

Michael — Wed, 21 Apr 2010 17:00:39 +0000

Q: I’m using Osage Orange for a sunburst top, and discovered it tends to color shift to brown. Is there a finish or other method you know of to prevent this?
A: Many exterior coatings, both oil based and waterbased, contain UV absorbers or blockers. These help, but to be honest, they really only delay the inevitable. Eventually, the sun always wins. Obviously, keeping the item away from light extends the time it will hold its color, but that is not always practical. There is a cheap and dirty trick that we often use for woods like Osage and purpleheart, and it works to some degree. Basically, you dye the wood with the same color dye as the wood itself, using a largely lightfast dye. Thus, the dye holds its color even if the wood loses its color. Irgasperse dyes, such as the TransTint concentrates sold by Jeff Jewitt, are surprisingly lightfast and would be a good choice here.

Sunblock for your wood

Michael — Wed, 16 Dec 2009 17:00:06 +0000

Q: I am a novice wood turner and want to minimize the loss of the vibrant colors found in many of the woods that I have spent lots of money on. I heard of something about Ciba Lignostab 1198 Wood Stabilizing additive. Is this for me? Any information would greatly be appreciated.
A: Traditionally, the way to block fading from sunlight is with UV inhibitors. There are three basic types: UV blockers, UV absorbers, and HALS. Blockers generally cause a loss in clarity, while absorbers and HALS do not. The most common of the UV absorbers are ketol enol reaction products made by Ciba under the Tinuvin brand. They work best when used in conjunction with HALS (hindered amine light stabilizers), also made by Ciba.
These products are added in proper amounts to the finish itself, thus adding UV and color protection. Many exterior coatings contain them. Because of the problems formulating with them, they have not been sold to the general public as a user added material.
Ciba Lignostab 1198 is a new breed of HALS designed to work in the wood itself instead of in the finish. It, too, works best when paired with a finish containing UV absorbers. Knowing Ciba’s long and admirable history with such products, I have no doubt this one works just as they claim. However, they generally sell their products only to finish manufacturers or wood products manufacturers, and not to end users. To date, I have seen no evidence that they plan to sell this product directly to consumers either. If you find anyone selling it, please let me know.

Wipe on UV protection

Michael — Tue, 13 Oct 2009 18:12:24 +0000

Q: Can you suggest a product that offers UV protection and can be used like a rub-on poly?

A: Sure. Any oil based varnish can be hand applied, so choose any good exterior oil based varnish, marine or household, that boasts added UV blockers on the label. I like to use them uncut, applying by scrubbing them onto the wood with Scotchbrite® and wiping off with blue paper shop towels, but if you prefer working with a thinner material, simply thin it with mineral spirits. In addition, there are exterior wipe on finishes, the equivalent to exterior Danish oils, already on the market, though those usually have little or no UV protecting additives.

UV protection indoors

Michael — Fri, 02 Oct 2009 21:21:26 +0000

Q: I am using Lawrence McFadden’s wipe on polyurethane gel but my furniture often winds up in sunny locations. Is there any UV inhibitor that can be added to this gel or should I try rubbing on an exterior poly or marine varnish that has an inhibitor?
A: The short answer is that it would be a whole lot easier to simply use an exterior varnish as your wipe on finish. While there are UV blockers and absorbers you could theoretically add to an interior one, they are not easily available. They are usually only sold to formulators, in part because their use requires a good bit of formulating information. The amount to be added is typically controlled by the resin weight, something few people outside the person who formulated the mix are likely to know.