Enhancing natural colors of wood

Bringing out the reds and yellows in koa. October 24, 2001

Question
We work with a lot of Hawaiian koa wood. Some epoxy and urethane finishes bring out the natural reds and yellows in the wood while others don't. I have been told that certain acids (acrylic?) in the materials are responsible for this. We are relying on extensive trial and error to find the color enhancement we are looking for, but can't always achieve it. Can anyone tell me what is responsible for this color change, so that we might formulate our own topcoat with this in mind?

Forum Responses
Different chemistry of products will have different results. If you want true natural colors then you want a product with very good "wetting" properties. Otherwise, I would use a slight dye on the pieces to pop some of the colors you want to get. It would add a step, though.

Bob Niemeyer, forum technical advisor

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When you chemically "stain" wood, which is what I believe you think is happening, it is also dependent on the mineral content of the wood. So a different tree of the same species could stain a different color due to minerals in the soil in which it grew. As to the exact chemical that is doing the enhancing, an MSDS sheet should pin it down pretty well if you are familiar with chemical stains.

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You could use a "Pad Stain" available from all the large finish suppliers. We apply by hand with a cotton cloth (T-shirt scrap) on top of sealer or first lacquer. Practice on scrap to get the desired effect.

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You could make your own pad stain to do your hand padding with. Take some NGR, reduce it with denatured alcohol till you're close to what your desired color strength would be, and then add water. The water will lessen/weaken the pad stain's bite into the lacquer.

Your application rag is not that big. It should fit in the palm of your hand. It is commonly folded in the shape of a Persian/Middle Eastern pastry called a "hamantashen". Assuming that few people are familiar with this pastry, let's just say that the pad/rag is shaped like a small triangle.

In your other hand should be a cotton rag which is dampened with denatured alcohol so that you can blot any mistakes and also so that you can mottle the hand padding.

When hand padding, you want to mute the color edges for subtle effects of your color swath.

Just as a side note, neither pad stains nor hand padding techniques are mentioned in any finishing books at all.