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DIY Torrefied (Roasted) Maple Violin Bridge
Proposed methodology of DIY Torrefied (Roasted) maple violin bridge, spruce sound post, and other small objects.
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Irv
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February 11, 2018 - 7:34 pm
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I have a second batch of violin bridges and a cello bridge in the oven.  2 hr at 390 F upper rack position convection fan on--no effect.  Raised temperature to 395 F (I know that 400 F works).  I also put in 2 each ebony violin bridges since I had them.  

I am now questioning the figure of 380F for maple I heard in a video.  He was an end user and not someone that did the toasting.  I did an internet search and could not find specific temperature numbers for any given wood species.  I think that this is a "trade secret" area.  I did find that researchers in europe "deep fried" wood to toast it (not specified in article, but I bet they used non flammable heat exchange fluid) to avoid using nitrogen.

I don't have any spruce available but I have a lot of cedar so I was going to cut some of that up tomorrow to see at what temperature that toasts at.  They are both softwoods so the temperature should be similar.

I have read that toasted wood is more difficult to glue than regular wood.  I will use the cedar to look into that.

I also read on the internet that attempting to roast wood without all the water removed will cause a mottled condition which is unattractive.  Water (and steam) is excellent at heat absorption so that is understandable.  

I am bidding on some violins with broken necks so I should have some front and back material to work on soon.

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Ferenc Simon
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February 11, 2018 - 9:18 pm
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Hmm... are you sure of the temperature though? What I noticed with convection ovens during regular cooking for example is that the temperature varies greatly between brands even as much as 20 degrees.. I have one that's consistently about 20 degrees colder than another if I set both to 200 C. Maybe if you have a multimeter with a temperature sensor you can somehow stick that in and compare, till you figure out the oven you bought. 

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Irv
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February 12, 2018 - 12:27 am
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Hi Ferenc Simon.  I could not agree more with you about the oven temperature.  I believe that it is keeping a consistent temperature but I have no clue as to "Natural Bureau of Standards" accurate temperature.  After all, I only paid $40 for it new through a Amazon Warehouse deal LOL.  I have several multi meters but lack the temperature sensor.  I do have a digital "meat probe" that I could calibrate at 32 F and 212 F, create a graph and compare it with "displayed" temperature of the toaster oven.  Same technology.

I am finding out that the "toasting" is very temperature sensitive in that no effect is observed at 2 hr at 395 F (displayed) and a very significant change occurs at 400 F (displayed).  Things that I have found out thus far.

1.  A small amount of pre treated (2 hr at 200 F "displayed" to remove moisture) saw dust appears to be an effective oxygen "getter"  when use in combination with an aluminum foil enclosure.  I am using 1/2 teaspoon per violin bridge.

2.  400 F (displayed) appears to be the magic temperature for maple.  

3.  You have to watch out for ebony inserts or you will lose them.  I am trying a batch now that were not shaped to see if I can put a drop of super glue on them after the roasting to hold in the ebony.  

4.  The roasted bridges definitely have a "ring" to them when dropped.  I have not autoclaved them yet so this might not be a final property.

I plan to send some of the bridges to Fiddlerman so that he can have his luthiers look at them.

I am definitely having some fun with my $40 investment with the toaster oven.

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Irv
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February 12, 2018 - 10:57 pm
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Hi Ferenc Simon (and others).  You were right, the digital reading of my toaster oven was way off!  It was reading 400 F and my meat thermometer said that the oven was 348 F.  I then found a laboratory mercury thermometer that went to 400 F, so I put that in and it read 346 F (it's a good thing that I don't live in California, or that mercury thermometer would give me cancer).

I don't know what type of paint they use for the manufacturer's logo on a maple violin bridge, but roasting has no effect on it (perhaps they burn them on).  All of the ebony inserts were intact on this batch, but I will superglue them to be sure.  

The roasting effect on the cello bridge is not as pretty as on the violin bridges, so I am going to try a different packaging arrangement before I attempt to roast another one.

I am going to keep raising the oven temperature until I see some effect on ebony.  No joy as of yet.

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Irv
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February 15, 2018 - 4:25 pm
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I just found out that the building code in Massachusetts (the next state over from me) requires spruce studs, joists, and rafters.  So I now found an inexpensive supply of spruce material for my roasting experiments.  

I ran my first samples through an autoclave and they still "click" when dropped.  

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Irv
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February 16, 2018 - 3:09 pm
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I just took out the 2 maple violin fingerboards and saw tears in the aluminum foil wrapping and faint areas of oxidation in the maple immediately around the tear.  I think that it will sand out, but I will use a more robust method of sealing larger items in the future.  I have thicker aluminum foil.

I saw in a Youtube video that luthiers were not able to bend wood after it had been roasted.  I will try to see if wood that has previously been bent will retain its shape when subjected to roasting.

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Irv
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February 18, 2018 - 4:15 pm
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By doing multiple roastings I have determined that what is taking place is a one time chemical reaction in the wood and you cannot look at it in terms of cooking.  If, for example, you extend the time of the roast or have it occur at a higher temperature than needed, no additional effect occurs (the wood does not get any darker).  This is important because I am introducing a shrink wrap vinyl film as an intermediate between two aluminum foil layers to prevent item loss in the event of a tear in the aluminum foil (losing a Chinese violin bridge to oxygen is of little importance, but losing a maple fingerboard begins to hurt the pocketbook).

The first photo is of a spruce wood sample after roasting, showing how the saw dust is almost consumed by oxidation.  The second is of wrapped items.  spruce-photo.jpgImage Enlarger_Aluminum-Foil-Photo.jpgImage Enlarger_

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Fiddlerman
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February 19, 2018 - 10:23 am
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Irv, we do not have anything like that as of yet but I'll keep you in mind of we receive a broken violin that we intend on trashing. 🙂

"The richest person is not the one who has the most,
but the one who needs the least."

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Irv
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February 19, 2018 - 6:38 pm
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I just purchased a 3/4 sized old german violin for $20 that I thought would be perfect for my experiments (1 piece front and back) but it is so nice that I hesitate to destroy it.

I have been trying to find a temperature where a "Freeze Rite" vinyl cooking wrap melted but retained a sealing layer between two sheets of aluminum foil.  It looks like 360 F (actual temperature) is the magic number.  I believe that this is the secret to roasting larger items without aluminum foil failure.

I graphed the roasting oven temperature error and will edit my previous posts to provide actual (mercury thermometer) readings.  I think that this is important since the internet appears to be providing wildly misleading information and making this process appear more difficult than it is.

My next step is to see if roasting makes it harder to glue the wood.

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