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I have been looking at research reports on the stabilization of wood by heating in the absence of oxygen. The modern use of this technique was initiated by the U.S. Navy when it could not obtain Teak wood. It is generally called Torrefied wood, although it is also called retiwood, thermowood, and platowood. It is excellent for decks since it resists moisture damage without the use of chemicals. It is now being used in the building of guitars. The process is comprised of three components.
1. Heating the wood at (edited: 210 F) to drive off moisture. Edited: Time required for a violin bridge is about 2 hours. A violin fingerboard takes 4 hours. Also heat a small quantity of saw dust to act as oxygen "getter."
2. Heating the wood to 180 C to 230 C (wood species dependent) in a nitrogen atmosphere for 24 to 48 hours. The magic temperature for maple is 194 C. Edited: It was found that wrapping the item tightly in aluminum foil with a small amount of dried saw dust made it possible to roast wood without the need for nitrogen. For larger objects, the use of a vinyl baking wrap such as Freeze Rite between aluminum foil layers prevented oxygen from reaching the object in the event of a stress tear in the aluminum foil. By experiment (see below), a maple violin bridge with 1/2 teaspoon of saw dust was roasted in 2 hours at a temperature of at least 330 F. By experiment, a large object such as a maple violin fingerboard took about 6 hours at a temperature of at least 330 F with about 3 teaspoons of sawdust.
3. Rehydrating the wood in an autoclave to restore workability. Edit on 3/7/18: I tried an autoclave on maple violin bridges and the lutheriers at Fiddle Shop thought that they were not "crisp" enough. I now don't autoclave and allow the roasted parts to naturally regain some moisture content in the air surrounding them.
The time of heating is for dimensional lumber.
I think that this process could be a DIY project on a thin object such as a violin bridge or sound post. Suggested method to try.
1. Heat a number of maple violin bridges in a metal pot in an oven at 212 F for about 1 hour.
2. Cover pot with aluminum foil and replace air with nitrogen or argon. Continue slight flow of gas and return to oven heated to 380 F for 2 hours. Edit: by experiment, no need for use of pot or need to replace air with nitrogen or argon due to use of aluminum foil to seal off air and a small amount of saw dust to consume contained oxygen within aluminum foil containment.
2 (alternate) Cover pot while in oven and remove pot. Remove each item quickly with forceps, tightly seal with multiple layers of aluminum foil, and return to covered pot. After all items are covered with aluminum foil, return uncovered pot to oven and heat to 380 F for 2 hours. Edit: need to put saw dust with item covered with aluminum foil. By experment, temperature is 330 F for maple.
3. Remove pot from heat and allow to cool.. Remove aluminum foil if necessary. Place items in autoclave. Edit: aluminum foil must be removed before placing in autoclave.
3 (alternate) Remove pot from heat and allow to cool. remove aluminum foil if necessary. Place items on metal screen above pot of boiling water for 1/2 hour. Edit: need to remove aluminum foil before placing on metal screen.
The aluminum foil idea is a slight modification of an old tool maker trick for heat hardening steel parts without the development of an oxidation crust. The original trick called for hammering stainless steel foil over the part.
Success is the progressive realisation of a worthy ideal. —Earl Nightingale.
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I did look at that thread before I posted the above since I vaguely remembered something on the Forum.
I did read something elsewhere that one of the methods of determine a mis-represented (fake) antique violin is to shine a light through the wood. Old wood is opaque, and new wood will let the light shine through it. Torrefied wood of any species is opaque. Another technique bites the dust.
A nice piece of equipment that could be used as a very precise oven that would also have gas regulators is a gas chromatograph. I just got rid of several of them when my wife retired from running a lab. Can't keep everything (although I try).
I am attempting to post things that people can do for themselves. I just got some ebony violin bridges from China, which should be interesting.
Success is the progressive realisation of a worthy ideal. —Earl Nightingale.
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I just microwave them. But my bridge blanks hang under a room lamp and the slight heat from that tends to remove moisture. If the blanks are microwaved too long a dark area appears in the center and I consider it a lost blank. I wait to microwave until after I have them carved. Also I rub(hard) the finished bridge on a scrap piece of flat oak. I do not know if any of this helps or hurts. Its just what I do.
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Irv said
2. Cover pot with aluminum foil and replace air with nitrogen or argon. Continue slight flow of gas and return to oven heated to 380 F for 2 hours.
I think there will be problems with this unless you have an oven specially modified for this purpose. Most tubing can't handle 380F. The kinds that can (like copper) tend to be pretty rigid, so they're either going to crimp, or hold the oven door open. The oven MIGHT be able to maintain 380F for 2 hours with the door open a quarter inch crack, but it might not - that's a lot of potential for heat loss. And of course, putting your source of nitrogen in the oven with everything else is... how shall I put this... risky?
On the aluminum foil idea, two things that might help:
If you can find sealable bags that can take that temperature, use a vacuum sealer (like they use for sous vide cooking) to get all the air out. (I'm not sure such bags exist, though.)
A for-sure doable alternative to that would be to wrap them in a aluminum foil, as you suggested, then put them in a sous vide bag and take the air out that way. You'll have to cut the bag off to keep it from melting, but the pressure will help force the aluminum foil to more tightly wrap the bridge.
If you don't have a vacuum sealer, you can do the same thing with a manual suction device (you can get starter kits for $25 or so) or dip the bag in water (although that won't provide a lot of pressure) or if all else fails, mostly close the bag and suck the air out with your mouth. (In all cases, this is only to help the aluminum foil fit more closely - it won't create a vacuum that will stick.)
I'd also recommend using the lightest aluminum foil you can find. It's going to be hard to get it to conform to all the nooks and crannies in a bridge.
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Hi Charles (and others). My thought on the tubing was to use 1/8" copper tubing with a Swagelok fitting on the regulator side. Inexpensive and widely available. I have also used 1/16" stainless steel but I don't see the need for this. I would use a needle valve set by placing the tube end in water and looking at the bubble rate. My oven has a soft cloth gasket and the tubing would easily fit through it. Since argon is heavier than air, very little would be lost from a container. You might not need to add any argon to the container while in the oven at all once filled and sealed with aluminum foil outside the oven.
There are going to be some voids in a bridge that the aluminum foil will not conform to. My thought on those would be to fill them with saw dust and any available oxygen will attack the dust because of its larger surface area. I think that I would use thick foil because it would form a more robust seal and avoid tears. Which one is better can only be determined by experiment.
I did see a luthier tool for setting guitar tail stocks that was a wood frame with a piece of silicone gasket material. The frame was placed on the guitar top plate over a freshly glued tail piece. A vacuum was applied to the frame and the silicone gasket material pinched down to hold the tail piece to set without the use of other clamps. Something like this would squeeze the aluminium foil to conform to the bridge, but might tear it. I think that saw dust is a better and cheaper solution to this problem.
Success is the progressive realisation of a worthy ideal. —Earl Nightingale.
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I am liking the saw dust idea (in vacuum deposition work, the saw dust would be called "the getter"). Moisture would first have to be removed from the saw dust, so it would be tossed in the pot with the violin bridges in "Step 1."
Success is the progressive realisation of a worthy ideal. —Earl Nightingale.
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MrYikes said
I just microwave them. But my bridge blanks hang under a room lamp and the slight heat from that tends to remove moisture. If the blanks are microwaved too long a dark area appears in the center and I consider it a lost blank. I wait to microwave until after I have them carved. Also I rub(hard) the finished bridge on a scrap piece of flat oak. I do not know if any of this helps or hurts. Its just what I do.
The source for my roasted maple guitar necks told me that they are roasted before they are carved. They specifically noted that it is not just a surface treatment.
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This process is definitely not a surface treatment. That is why it takes several days to "roast" dimensional lumber. However, due to the large surface area to volume in a violin bridge or sound post, it should only take a few hours to heat treat them. I would think that you could easily do a hundred at at time if you could space them (blanketed in an inert gas). The gas is obviously used to shield the wood from oxygen. Torrefied wood is basically the early stage of making charcoal in an oxygen free environment.
Success is the progressive realisation of a worthy ideal. —Earl Nightingale.
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The sawdust sounds like an excellent idea. You might even go to the length of putting down a layer of sawdust, then the bridge, then more sawdust to cover it. Make it roughly square and the aluminum foil will fold easily. (I suggest more sawdust to try to get all the oxygen eaten before the heat gets to the bridge.)
The neutral gas would be better with the stuff to pull it off, but I doubt I could with my stove. I really like that sawdust idea, though.
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Adding more sawdust should not bother anything, but should be kept to a reasonable limit since sawdust is an excellent insulator (that is how they kept ice cold aboard ships and in ice houses) so you would need to keep the parts in the oven for a longer period. I think that a thickness of 1/8" or so and filling in the bridge heart should be more than adequate if the seal is tight.
Keeping the oven at 380 F should also keep the temperature below the ignition point of cellulose (which I think is 454, the title of that famous book).
Edit: By experiment, a maple violin bridge was roasted at a temperature of 330 F or greater. By experiment, it was found that a large quantity of saw dust acted as an insulator and greatly lengthened time requirements. By experiment, it was found that 1/2 teaspoon of previously oven dried saw dust was adequate for a violin bridge, and slightly more was required for a cello bridge or a violin fingerboard.
Success is the progressive realisation of a worthy ideal. —Earl Nightingale.
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This thread seems to be getting a lot of views. I think that it is time that we take it from conjecture to "proof of concept." I will haunt the local Goodwill outlet and see if I can get a $20 toaster oven or similar. The most excitement appears to be in the aluminum foil idea with the use of wood chips as an oxygen "getter," so I will do that first. I also have a tank of argon so I will do that as a back up and see if there is any difference in the methods.
The next logical step would be to use torrefied maple as a violin finger board, so I will try to find a toaster oven with a large enough capacity to fit a board of this length.
Success is the progressive realisation of a worthy ideal. —Earl Nightingale.
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Some of the guitar manufacturers have had good luck substituting roasted maple for ebony. We all know how good ebony has become harder and more expensive to obtain and guitar fingerboards are even larger than those for violin. One of my guitar fingerboards (actually the whole neck) is roasted maple and I am VERY happy with it. One of the benefits of roasted maple is that it doesn't require a finish for protection from moisture and when sanded to a sufficient grit is slicker than varnish, lacquer or any other treatment.
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I just ordered a Black & Decker convection toaster oven with a digital (thermister) temperature regulation with a capacity large enough to do a violin finger board. It has cosmetic damage but I have no plan of putting it in the kitchen. I already have an autoclave.
Success is the progressive realisation of a worthy ideal. —Earl Nightingale.
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Very interesting ideas.
Looking forward to seeing follow up threads on this.
"The richest person is not the one who has the most,
but the one who needs the least."
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I already have violin and cello bridges and a couple of spruce sound posts. I was going to order two carved maple violin fingerboards and a maple tail piece from China to see how they go. Anything else of interest?
Success is the progressive realisation of a worthy ideal. —Earl Nightingale.
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The Black and Decker toaster oven came in and I have started to experiment (the toaster is adequate for my needs but I do not recommend its purchase to others since it was built to an extremely low level of quality spec).
I started with three violin bridges. I used about 1 oz of sawdust per bridge, wrapped in standard household aluminum foil in a multiple fold configuration to avoid air leaks, and placed in the toaster oven on a low grid at a temperature of 380 F. (Edit: the digital temperature setting on the oven was found to be in error. 380 F oven display was found to be 310 F actual temperature by mercury thermometer) 1 bridge was removed at 2 hr, the second was removed after 4 hr, and the third removed after 6 hr.
There was no observed change in the first bridge. The saw dust was "toasted" in the second with no observed change in the bridge. The saw dust was "toasted" to a deeper color and the bridge was slightly toasted at 6 hr.
It is bad experimental design to change multiple parameters at the same time but that is what I did for the second attempt.
It was obvious that too much sawdust was used and that it acted as an insulation layer. So only 1/2 teaspoon was used for each bridge in the second attempt. The metal grid was put in the upper position to raise temperature (hot air rises). And the oven temperature was raised to 400 F. (Edit, 400 F oven display was later found to be 340 F by mercury thermometer).
I am currently running the second attempt, but can tell you that the first bridge (2 hr) came out darker than the 6 hr bridge in the previous attempt. That is encouraging since my oven only goes up to 450 F.
Success is the progressive realisation of a worthy ideal. —Earl Nightingale.
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It Werks!
Slight problems in that the aluminum foil was inflated like a ballon on the 4 hr sample (I did not take the time to remove the moisture step since I was using the same sample as the previous day. It was obviously moisture but there was not enough to damage the foil) and an ebony insert (previously super glued in place) was removed on the 6 hr sample.
Deep brown color in all samples and they sung like ivory guitar nuts when dropped. I will take pictures. No odor is given off while roasting since the aluminum foil acts as a shield.
Next up for the oven are more violin bridges and two cello bridges. I also have some ebony violin bridges that I purchased a while back. No idea if 390 - 400 F is the proper temperature to roast them (Edit: 390 - 400 F was based on oven digital display, which was found to be in error. 390 oven digital is 340 F actual). I am going to try 390 F (if I can make that temperature adjustment on the digital display). I have some maple violin fingerboards coming from China but no idea when they will arrive. I have a hard time justifying the purchase of maple tail pieces since I can get ebony cheaper.
What I need now are some spruce violin tops and maple violin backs (the oven is large enough to fit them in). Both the fronts and backs will have to be one piece (no way could I reglue a "book matched" back). If I can get some violins with damaged necks, I think that I could remove the varnish by "bead blasting" with baking soda and put the violin in the oven at 200 F to loosen the glue. Then I put the front and back in aluminum foil with saw dust and roast them.
In theory I could protect the ribs from the bead blast by masking tape and could reglue the bodies after roasting. But mainly I just want to see if the plates deform then roasted.
So Mr. Fiddleman "@Fiddlerman", do you have some violin shipping mashes you could donate to science?
Success is the progressive realisation of a worthy ideal. —Earl Nightingale.
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I am thinking ahead to when I try to toast a more "dimensional" piece of material like a violin finger board. I will continue to swap each finger board with aluminum foil and will include a small quantity of saw dust. I am thinking that the best way to determine the length of time required for the roast would be to include a test piece of the same type of wood with equal width and depth, and drill a tight fitting hole at the end of it for a digital meat thermometer with a cable for an external digital display. Corning makes a high temperature (800 F) silicone caulk for sealing flue pipes that should prevent air from entering the aluminum foil at the temperature probe cable penetration.
Success is the progressive realisation of a worthy ideal. —Earl Nightingale.
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I took a photo of the 3 violin maple violin bridges I previously roasted. An unroasted bridge for color comparison is in the upper left. 
_
Success is the progressive realisation of a worthy ideal. —Earl Nightingale.
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