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| Correcting walnut color change from bending http://luthiersforum.com/forum/viewtopic.php?f=10101&t=35465 |
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| Author: | David Malicky [ Mon Feb 20, 2012 3:26 pm ] |
| Post subject: | Correcting walnut color change from bending |
I'm trying to decide how to fix a color mismatch between a back and bent sides. The claro walnut I started with had a nice reddish hue (pic below, on right). After bending, the sides lost almost all the red hue and have a grey/green shift (on left, though the pic doesn't really show the green). I'm guessing I bent too hot... had springback at 305F with some other walnut, so went to 315F, but I don't think this claro needed or wanted it. Next time I'll bend the off-cut first to check! Now I'm uncertain how to fix it. I mixed a few drops of reddish mahogany dye with shellac and can get the bent wood to pretty closely match the original (w/ untinted shellac). But I know for at least some woods, natural red hues don't stick around over time, so I wonder if the back will lose the red in a few years, while the sides keep it! I've no experience with claro walnut colors over time to know. Or, I imagine I could put the heating blanket on the back panels to color shift them, too, but not sure how even it would come out, or if it would ruin them by warping. Or I could tint them both a darker red, but that may look unnatural. So, I'm confused. What has worked for any of you? All advice appreciated. |
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| Author: | mcgr40 [ Mon Feb 20, 2012 3:40 pm ] |
| Post subject: | Re: Correcting walnut color change from bending |
My experience has been that walnut will lose the red/purple color when exposed to light- the variations in colors within a piece will stay relatively the same(really gets a bit muted over long periods). If you finish the pcs as is, they will probably look close to even in a few months. Any time I tried to add some red to the color of walnut- which always seemed at the time to be a good idea- I have been disappointed with the results within a few weeks after finishing- perhaps that has just been my error. It is my experience, though. |
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| Author: | Corky Long [ Mon Feb 20, 2012 3:41 pm ] |
| Post subject: | Re: Correcting walnut color change from bending |
What does it look like with a washcoat of naptha? I sometimes find that perceived differences in color are much less noticeable when the finish actually goes on. After pore filling and finishing the difference might be less than you're seeing now. What do you plan to finish it with? A ZPoxy pore fill will add a bit of amber hue to it as well, which some don't like, but it can come in handy in cases like these. |
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| Author: | runamuck [ Mon Feb 20, 2012 4:46 pm ] |
| Post subject: | Re: Correcting walnut color change from bending |
mcgr40 wrote: My experience has been that walnut will lose the red/purple color when exposed to light- the variations in colors within a piece will stay relatively the same(really gets a bit muted over long periods). If you finish the pcs as is, they will probably look close to even in a few months. Any time I tried to add some red to the color of walnut- which always seemed at the time to be a good idea- I have been disappointed with the results within a few weeks after finishing- perhaps that has just been my error. It is my experience, though. My experience is just the opposite: walnut warms up over time, taking on subtle yellows and reds as it oxidizes. My guess is that once you sand the sides the warm hues will return. The grey tones will definitely lessen with light and air. |
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| Author: | kjaffrey [ Mon Feb 20, 2012 5:05 pm ] |
| Post subject: | Re: Correcting walnut color change from bending |
On the several (4 or 5) walnut guitars I have done I remember noticing color variance after bending, and on the first couple I remember being concerned about the differences, but after the guitars were sanded and finised the problems either went away, or weren't really noticeable. Remember the sides and back are in different planes anyway so the sublte color differences are not as obvious then, especially when under finish. Hope your experience works as well as mine did. Kent |
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| Author: | Stuart Gort [ Mon Feb 20, 2012 5:07 pm ] |
| Post subject: | Re: Correcting walnut color change from bending |
The same thing happens to me when I have to bake Walnut to correct warpage. It works very well to correct even severe warpage but it certainly washes out the color a little. I pretty much get the exact same result as your photos indicate. So....I take two bookmatched plates meant for carved top electrics (.5" thick in their raw state after resaw) and I sandwich them between two aluminum plates (.25" each plate). Then I use 6 C-clamps to flatten the whole business. Experimenting, I've used several heating profiles and gotten the same result every time. I'll list the following two extremes and you can probably use either or interpolate another schedule from this info. 320F for two hours. I set the timer for two hours upon setting the oven temp...so this includes the pre-heat in our house oven. (the wife is a sport). 275F for four hours. Same thing with the pre-heat. After it's done make sure you let it cool down overnight to make sure it's room temp before you unclamp. Also, it's going to be drier so you should store it for a while stickered and under enough pressure to keep it flat while it once again reaches equilibrium. Finally, I haven't gone less temp or time than the above schedules. It might work very well to use 220F for two hours, for instance. If you're worried about wrecking your walnut you may want to sneak up to a workable schedule. At any rate....only baking that back is going to produce a match to your sides. Once you bake the color out of the wood....it's not coming back. I've straighten a BUNCH of panels doing this but I avoid doing it because of what it's done to the color..of WALNUT. Baking has done some WONDERFUL things to the color of Maple and Myrtlewood. Note that you can experiment with a particular species by using small pieces and small aluminum plates that match that size. The plates homogenize the heat because aluminum conducts heat very efficiently. The concept scales up and down quite accurately. |
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| Author: | cphanna [ Mon Feb 20, 2012 6:11 pm ] |
| Post subject: | Re: Correcting walnut color change from bending |
If I were in your situation, I wouldn't worry about trying to match the color. However, whatever I did to the sides I would ALSO do to the back plate. I am pretty sure they'll look very closely matched under a finish. I'd love to have a chance to work with claro some day. I've worked with literally hundreds of board feet of black walnut, but never claro. I suspect they are very similar in the way they takes finishes, but you'll need to hear from someone who has worked with both to confirm that. Having said that, a lot of black walnut gets steam-treated at times in the kiln. This tends to even out the color somewhat, and it drives some pigment into the lighter sap wood. Lots of flooring and furniture manufacturers want to buy it this way, so it's done this way. The process does tend to make the natural brown turn sort of gray, but it always warms up nicely under a finish--even with no staining. I almost always stain walnut with oil stains and I mix in a little red for warmth. I add these stains to my pore filler, and most of it gets removed from the surface, but the warmth remains. I've been doing this on furniture, frames, carvings, etc. for 40 years. I did it on my classical and archtop guitars and on a mandolin. I am about to do it on a second mandolin. I have used this method under nitro and water borne lacquers, under various oil varnishes, under poly varnish, and under rubbed oil finishes. I have never had a problem with the warmth fading--even after decades. |
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| Author: | Alex Kleon [ Mon Feb 20, 2012 6:11 pm ] |
| Post subject: | Re: Correcting walnut color change from bending |
Kiln drying does the same thing to walnut - it gives the wood a bit of a grey cast. Once you get some finish on it, it will look a lot better. Alex |
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| Author: | David Malicky [ Tue Feb 21, 2012 4:37 pm ] |
| Post subject: | Re: Correcting walnut color change from bending |
Thanks, all, for the tips -- very helpful! I tried ~clear shellac on each and unfortunately the color match is still not very good, even with the panels perpendicular to each other. Sound like red dye is to be used with caution. Yes, I was thinking of Zpoxy, so that may help some. I think I'll first try sanding to see what that does, and also put scraps of each wood in a window for a few weeks to check UV changes. If those don't work, I'll try some heating schedules on the back as Stuart suggested, starting with scraps. Unfortunately the back is already joined, braced, and profiled so I'm hoping an easy route will work, but I don't mind redoing those steps if heating the back is needed to get a good result. Hopefully, some combo of UV, sanding, a tiny bit of red dye, and Zpoxy may do it. That's interesting how baking de-colors walnut and colors maple and myrtle. Makes sense, though. Good to know about the flattening procedure--thanks. On steamed black walnut, I have a bunch of dark brown/purplish black walnut from a hardwood store... I've been guessing it has been steamed? I was also given a few boards of light and ~uniform colored walnut -- almost no smell to it at all when sanded... wish I knew what it was. |
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| Author: | Kevin Waldron [ Tue Feb 21, 2012 11:41 pm ] |
| Post subject: | Re: Correcting walnut color change from bending |
Not trying to critcize but you guys need to do a little research. We have operated several kilns for almost 40 years. To begin kiln drying does not necessarily change the color of wood, especially walnut. Cooking wood rapidy ( such as an oven ) in most cases causes Case hardening.......This will happen to lumber or timber that has been improperly kiln-dried. If dried too quickly, wood shrinks much at the surface, compressing its damp interior. This results in unrelieved stress. Case-hardened wood may warp considerably and dangerously when the stress is released by sawing. This is from Wikipedia and it applies to thin wood as well. Years from now the damage will come to light even if it doesn't show now. The material will be much more brittle and stressed much more than the age it reflects. American walnut with time lightens to a creamy brown color ........ look at old antiques...... 25-100 plus years or more One way to change the coloring of walnut is to bleach and re-dye ...... or use dye to make everything the same color....... all will lighten but will do so more or less together. In the case of walnut it will lighten with sunlight where as woods like cherry will darken with the light. Blessings, Kevin Waldron |
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| Author: | cphanna [ Wed Feb 22, 2012 2:09 am ] |
| Post subject: | Re: Correcting walnut color change from bending |
David, I'm sorry you're not happy with your present color match, but I still think you'll be okay in time. Regarding your rich brown / purple-ish black walnut, I would guess that wood has NOT been steam treated. I've had some beautiful walnut that exhibited those colors, too. It's wonderful stuff. And to clarify, I did not mean to imply that all lumber companies steam treat their walnut. Some do, because they have customers who request it that way. My archtop was made from kiln dried, steam treated walnut. I acquired it directly from the company that processed it. That particular walnut warmed up under a finish just as beautifully as any other walnut I've ever had. Man....I love walnut. |
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| Author: | David Malicky [ Fri Feb 24, 2012 1:45 pm ] |
| Post subject: | Re: Correcting walnut color change from bending |
Kevin and cphanna, thanks for the helpful info! Yeah, I love walnut, too! |
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