Color and Shade Issues in Book-Matched Veneer

      Sawing can create a "light side" and a "dark side" on veneer pieces, leading to visual appearance issues in bookmatched veneer layups. Here are some explanations of the issue and some suggested solutions. July 26, 2005

Question
I have been book matching veneer, and I am wondering how to deal with color issues when book matching center-match positive and negative veneer. One stave looks different from the other in color and Im not sure why. Does anyone have any suggestions?

Forum Responses
(Veneer Forum)
From contributor J:
The light/dark is caused by one side of the veneer being open or broken. This happens during veneer cutting and is referred to as tight side/loose side. Place veneer between the palm of your hands and twist your hands, you can feel the difference.

Two things you could do are:

1. You can treat the veneer with glue siz. This helps to balance the absorption of top coats and finishes, leading to a more uniform appearance (Notice I did not say balanced, perfect finish).

2. You can eliminate the light dark issue of book matching by using veneer that has been cut on a lumber slicer. This method of veneer production does not result in loose side and tight sides.
Both surfaces of the veneer are the same.



From contributor F:
Contributor J is right on the money. You can also consider slip matching instead of book matching, and that will avoid the tight side/loose side and barber pole effect that is common with a book match.


From the original questioner:
What is slip matching? The architect requires book match. Is it similar? Or is it similar to sequence match?


From contributor J:
Slip matching is joining the leaves in sequence without flipping every other one.


From contributor L:
To contributor J: I searched the site and found several other mentions of lumber slicing, but no explanation as to what it is or how it's done. Is it slicing off pieces thick enough to class as lumber? Is such veneer common to find or a specialty item?


From contributor F:
To the original questioner: I would guess that the architect doesn't know the difference, he's heard book match and that's all he knows. If looks and sounds like a solution someone will have to enlighten the architect. Slip matching is less common than book matching, but slip matched sheets and faces are usually available from stock in many species from most veneer converters.


From contributor F:
I should have gone a little further. What is the species, and what is the cut that the architect has specified? This may have a bearing on a decision or direction. In fact, has the cut even been mentioned?


From contributor J:
To contributor L: You can see a lumber slicing video by doing the following

Go to:
www.fezer.com.br/eng
Click - products
Click - digital video
Click - slicing wood
Click - FM30

Here is what you are looking at. Imagine six pieces of wood going around in a circle - as veneer is peeled off, it is placed on the corresponding pile to keep it in sequence. The boards are taken across a knife which is at 75 degrees to the wood, and the veneer is peeled off of the bottom.

The pressure system is like a tank track made of rubber (like a giant rubber belt), and it transports and holds down the board across the knife. This system of slicing produces higher quality veneer than traditional methods.



From contributor K:
I believe the barber pole visual effect of book matching is due to reversed grain direction rather than the method used to produce the veneer. I have observed the same thing on book matched re-sawn veneer. The degree of contrast varies with the angle of the wood fibers to the panel surface. Slip matching will produce a more consistent look. Glue size or a wash coat of finish before staining may help to reduce the contrast.


From contributor C:
I agree with Contributor K. He described well what causes barber-poling. It is a side-effect of one of the properties that makes wood appealing: chatoyance, which is just a good Scrabble word meaning "changing luster" - sort of a mild version of one of those hokey 3-D pictures with the layers of polarized plastic on it. It is not a function of veneer manufacture, but the effect of light refracting differently off of the two (or more) leaves of veneer because they are flipped in opposite directions.

Some species, cuts, and figure types are more likely than others to result in barber-poling, but it also varies log by log and flitch by flitch (Contributor K's explanation should make it clear why).

As a side note, I've seen barber-poling used intentionally for aesthetic effect. I don't usually associate walnut with barber-poling, so changing flitches might be one way to deal with the problem. As the others have said, other solutions include changing the match and changing the architect/designer's mind (good luck).

As far as glue-sizing and wash coating in the finishing process, I doubt it will be successful if the barber-poling is extreme. The goal would be to kill the wood's chatoyance, which can be done, but I suspect that these two methods won't go far enough.



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